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c SCIENTIFIC MONOGRAPH No. 2
TTO JA IN
B,y
MUHAMMAD AFZAL B.Sc. (Agri.). A.I.C.T.A.
AND
M. A. GHANI" Ph. D. (Massachusetts), M.Sc. (Agri.). F. R. E. S.
PUBLISHED BY
ID
THE PAKISTAN ASSOCIA nON FOR THE ADVANCEME~F SCIENCE UNIVf:RSITY INSTITUTE OF CHEMISTRY ".
THE MAU_. LAHORE
42419
11111111111111111111111111111111111 IARI
PRICE Rs. 10/.
PRINTED IN PAKISTAN
AT THE RIPON PRINTING PRESS. BULL ROAD. LAHORE BY MIRZA MOHAMMAD SADIQ
FOREWORD
THE monograph Cotton ] assid in the PunJab published by Messrs M. Afzal and M. A. Ghani is the second monograph published by the Pakistan Asso
ciation for the Advancement of Science, the first being Plant Diseases of the Punjab by Dr. Abdus SattaI' and Dr. Abdul Hafiz. This monograph, describes the work done at Lyallpur by the authors under a scheme financed by the Indian
Central Cotton Committee for cotton jassid investigation in the Punjab. The authors have shown that jassids are the most serious pests of the cotton crop and that Empoasca devastans Dist. is the most important cotton jassid in this region. Cotton varieties such as 4F, L.S.S., 289F/43 and 199F have been proved to be resistant to this pest.
Study has also been made of the seasonal and annual vanatiOns in the popUlation of the insect, whose infestation starts towards the end of June or the beginning of July, i.e., six weeks after the sowing of the cotton crop. It reaches its peak by the middle of August and disappears in November. High atmospheric humidity has been found to be conducive to high population of the pest. The authors have found that hairy plants are resistant to this pest and have, therefore, suggested that in places where jassids are a serious pest, only hairy varieties of cotton should be grown.
It would not be out of place to mention that the ;;enior author is a cotton breeder of international repute and holds at present a very responsible post in the Government of Pakistan, Ministry of Agriculture. Hence the findings presented in this Monograph are of great value.
It is hoped this work will interest research workers in this special line as
well as other students of Agriculture. It should also help cotton growers to avoid heavy losses through jassid infestation by undertaking precautionary measures suggested by the authors.
UNIVERSITY INSTITUTE OF CHEMISTRY
LAHORE
] une la, 1953
KARIMULLAH General Secretary
PREFACE
The Jassid Research Scheme, Lyallpur, was sanctioned by the Indian Central Cotton Committee, Bombay, .in the cold weather meeting of 1937, and the work on the scheme was started on 1st April, 1937. The scheme was closed down on 28th February, 1945. The Indian Central Cotton Committee has thus financed this work for nearly eight year3 at a total cost of Rs. 22,145.
The staff consisted of one Research Assistant and one Fieldman. both of whom worked under the direction and guidance of the undersigned. Mr. Piare Mohan Verma. M.Sc., was the first Research Assistant, who worked for about two years, and was succeeded by Hafiz Manzoor Abbas, M.Sc. (Agr.), who worked for about four years and left the scheme in June. 1943. Mr. Abdul Ghani, -M.Sc. (Agr.) was 'then appointed Re3earch Assistant and worked till the scheme closed down. It is a great pleasure for me to record that all the Research Assistants worked very diligently and loyally.
The genesis of the Jassid Research Scheme is due to Mian M. Afzal Husain, formerly Entomologist to Government Punjab, who, during his stay at Lyallpur to the end of 1938, put the work of the: scheme on a proper footing, and the: successful prosecution of the work is in no small measure due to the inspiration I received from him. Even as Vice-Chancellor of the Panjab University and later as member of the Indian Famine Commission, he found time to discuss the various aspects of the jassid problem with me, and I am very grateful to him for the help and encouragement he always gave me in this connection. Dr. Nazir Ahmad, Director, Technological Laboratory, Matunga, designed the apparatus for measuring
'the toughness of the leaf-veins. I am very grateful to him for this assistance_ Mr. Dawarka Nath Nanda, Statistical Assistant, under the Punjab Botanical Research Scheme, Lyallpur, and Mr. Dil Muhammad Qureshi, Statistician, Department of Agriculture, Punjab. were responsible for all the statistical analyses presented in this Monograph. The fibre-testing work was done by Mr. S. Rajaraman, the Technological Assistant. I am very grateful to them for the help they have rendered. I am also grateful to Dr. Taskhir Ahmad for reading through the manuscript and making very useful suggestions for its improvement.
Finally, thanks are due to the Indian Central Cotton Committee, Bombay, whose generous grant made: this work possible.
LYALLPUR
October, 1951
1vh..rHAMMAD AFZAL
VI
CHAPTER
CHAPTER
CHAPTER
CHAPTER
CHAPTER
1. II.
III. IV.
V.
CHAPTER VI.
CHAPTER vrr.
COTTON JASSlD IN THE PUNJAB
CONTENTS
INTRODUCTION LIFE HISTORY AND SYMPTOMS OF ATTACK
Life history of E. devastans Description of various stages Symptoms of attack .
EMPOASCA SPECIES ON THE COTTON PLANT ... LIGHT TRAP COLLECTIONS OF JASSIDS
Collection of insects .. . Proportion of Empoasca. devastans and other species .. . Proportion of sexes in E. devasta7ls collections .. . Influence of weather conditions on the size of the catch
SPECIES OF EM POASCA ATTACKING COTTON PLANT IN THE PUNJAB
Method of survey Identification of species The species found in different places
STATUS' OF DAMAGE DONE BY THE SPECIES OF EMPOASCA TO THE PLANT
VARIOUS COTTON
Damage done to the plant by E. herri var. motti Damage done to the plant by E. de1Jastans
(i) Growth. in hei~ht (Ii) Flower and boH production
(iii) Technological properties of lint The cotton jastiid of the Punjab <wd its effect on
the plant HOST PL.I\NTS AND SEASONAL HISTORY 01" E. DEV AST ANS
Preliminary in vestiga tions Range of host plants Seasonal history
Page 1
2
2 2 4
5
7
7 7 H ()
]2
]2 12 13
F)
20 20 21 21 23
28
2()
29 30 32
CHAPTER VIII. POPULA nON OF E. DEV AST ANS ON THE COTTON PLANT IN THE PUNJAB ... 33
Method of estimating the population .,. 33 Standardisation of the methods of estimating population 34
Comparison of the three methods of estimating the jassid population . ." 3R
Comparative incidence of the pest on different varieties 42
Comparative incidence of the pest in different regions of the province . . . . 42
Seasonal and annual variation in the population of E. devastans on cotton 43
CONTENTS VII
Page
CHAPTER IX. AGE OF LEAF AND TASSID POPULA nON 48
CHAPTER X. EFFECT OF AGRONOMIC FACTORS ON JASSID POPULATION 52
Effect of date of sowing on jassid population ... 53 Effect of spacing on jassid population ... 53 Effect of spacing-cum-sowing date on jassid population 55
(i) Varieties 56 (ii) Date of sowing 57
(iii) Spacings 57 (iv) Interaction between varieties and spacings ... 58 (v) Interaction between varieties and sowing dates 59
(vi) Interaction between sowing dates and spacings 59 (vii) Interaction of the second order ... 60
(viii) The plant unit versus area unit for estimating jassid population 60
The yield of seed-cotton, from the complex experiment 61 (i) Varieties 62
(ii) Dates of sowing 62 (iii) Spacings 63 (iv) Interaction between varieties and spacings ... 63 (v) Interaction between varieties and sowing dates 63
(vi) Interaction between spacings and sowing dates 54 (vii) Interaction of second order ... 64-
Causes of variation in jassid population in different varieties, dates of sowing and spacings 66 (a) Moisture percentage 66 (b) Hairiness of leaf-veins 67 Cc) Toughness of leaf-veins {)9
Effect of irrigation on jassid population 71
CHAPTER XI. THE NATURE OF RESISTANCE 74 Egg-laying by female-; of E. devastal1s 74 Hatching percentage of eggs 75 Development of nymphs 76
CHAPTER XII. CHARACTERS OF THE LEAF-VEI0J ASSOCIATED WITH RESISTANCE 78
Thickness of the cuticle pH value of the cell sap Moisture contents of the leaf-veins Toughness of the cuticle Hairiness and toughness Population and toughness Hairiness and jassid population Hairiness of the leaf-veins
(i) Hair density (ii) Hair length
CHAPTER XIII. SUMMARY REFERENCES
..
78 78 79 82 84 84 84 85
S6 92 95 97
VUI CoTTON ]ASSlD IN THE PUNJAB
PLATE I
Fig. 1
Fig.:2 .
Fig. 3
Fig. 4-
Fig. 5
PLATE AND FIGURES
Opposite Page
4-
32
47
49
50
82
COTTON JASSID IN THE PUNJAB
CHAPTER I
INTRODUCTION
Jassids are well known all over the world as a serious pest of a large number of field and garden crops. A host of species have already been identi. fied, but a large number still awaits identification.
In the Punjab, jassids are the most serious pest of acclimatized American cottons. After the severe jassid attack and the subsequent complete failure in 1913 of 3F, the first variety of Punjab-American cotton introduced by the Department of Agriculture, it was realized that a high degree of jassid resistance was a factor of primary importance requiring study for the successful introduction of these cottons in the Province. Since that time it has been realized that no new variety of American cotton can be introduced in the greater portion of the cotton belt of the Punjab unless it is resistant to this pest.
With the inauguration of the Punjab Botanical Research Scheme jointly by the Punjab Government and the Indian Central Cotton Committee in 1925, the work of breeding new and better varieties of cotton was placed on a proper footing, and the need for finding out the reactions of these varieties to jassid attack was very keenly felt. With the increase in thE' area under these cottons, the necessity for a fuller knowledge of the species of jassids responsible for the damage, their life histories and habits, and the method of control, became more urgent.
It was also considered necessary to survey the alternative host plants in order to find out whether clean-up operations, which had been found highly satisfactory against spotted boll-worm in Sind and the Punjab, would be of any use in combating this pest. The nature and the extent of damage done by the jassids to the plant had to be investigated. and the characters of the cotton plant associated with susceptibility or resistance had to be found out so that the breeders could easily detect these plants in the field. Finally the association, if any, between jassid attack and agronomic factors had to be investigated so as to enable the Department of Agriculture. Punjab, to advocate suitable changes in the prevalent agricultural practices so as to avoid or mitigate the attacks .
..
2
CHAPTER II
LIFE HISTORY AND SYMPTOMS OF ATTACK
Life history of E. devastans
After mating, which usually takes place either In the early morning or late in the evening, and which, at times, may last for more than seven minutes, the females deposit eggs singly inside the prominent leaf-veins in the spongy parenchymatous tissue lying between the vascular bundles and the epidermis. The maximum number of eggs laid by a female, recorded so far, is '29.
The incubation period lasts for 3-4 days in summer and may extend to as many as 10 days during winter.
The nymphs emerge out of the same hole in the leaf·vein which was made by the female ovipositor at the time of oviposition. The nymphs undergo five moults before reaching the adult stage. The nymphal ins tars occupy 6-9
days in summer and 21 days or more in winter. The ,adults are comparatively lcng-lived and mated adults are known to
live up to 5 weeks in summer and 7 weeks in winter. The nymphs resemble the parents in all respects except that they do not
possess wings. Description of various stages
The description of the adult as given by Distant (1918) and of the immature stages by Afzal Husain and Lal (1940) is reproduced hereunder:Adult.·-"Head, pronotum and scutellum pale ochraceous; vertex with two
bJack spots on apical margin; face with the lateral areas more or less distinctly pale brownish; body beneath pale ochraceous; legs and tegmina pale greenish--ochraceous, the latter with a black spot near apex of each claval area; vertex of head short, conically rounded anteriorly, more than half as long as breadth between eyes; pronotum with three greyish-white spots near anterior margin; scutellum spotted with greyish-white; tegmina extending far beyond abdominal apex. Length inel. tegm. 3 millim." (PI. I, fig. 7)
Egg.-"Length 0.73 mm., breadth 0.24 mm. Translucent with a yellowish tinge when freshly laid, later turning greenish yellow. Elongated, slightly hooked towards the anterior end, the other end being broadly, pointed. When about to hatch, a pair of brownish red eyes shine through the chorion near the anterior end." (PI. L fig. 1).
First instar nymph.-"Length 0.6 rom. Transparent and yellowish when newly hatched, later greenish yellow. Eyes conspicuous, reddish brown and oval. Head with six dorsal spines along anterior margin. and a triangular area between eyes (apex pointing towards prothorax). Thoracic segments
LIFE HISTORY AND SYMPTOMS OF ATTACK 3
distinct, prothorax narrow in middle, posterior or lateral angles of mesoand meta-thorax .each with a spine, the hind pair of legs slightly longer than the two anterior pairs. Abdomen apparently nine-segmented, first almost as broad as fhorax, second with lateral conical projections distinctly broader than the other segments, third to eighth with long prominent lateral spines, each with a transverse row of four dorsal spines, knobbed at extremities, ninth segment narrowest and only slightly longer than the eighth". (Pl. I, fig. 2).
Second instar nymph.- "Length 1.03 mm. Differs from the first instar nymph in having eyes white superficially, dark-reddish underneath, in the proboscis reaching the third abdominal segment, a transverse greyish brown patch near posterior margin, rudimentary wing pads along posterior ends of sides of meso- and meta-thorax, hind tibire with two single rows of spines, second abdominal segment with rounded projections at sides and with two minute spines on dorsal surface, dorsal rOW of spines on segments three to eight with two very minute spines at sides,· abdomen broadest at third se~ment, ninth segment longer and narrower thall others. with a ring of spines along posterior margin and a pair on dorsum" . (PI. I, fig. 3).
Third instar nymph.-ICLength of male 1.23 mm. of female 1.33 mm. Yellowish green. Differs from the second instar nymph in having wing pads more prominent, each with a small spine on tip and indistinct greyish brown patches across posterior margins of meso- and meta-thorax, abdomen broadest at fourth segment". (PI. I, fig. 4).
Fourth instar nymph.-ICLength of male 1.50 mm., of female 1.69 mm. Head and thorax greenish yellow, abdomen bluish green, eyes greyish purple. Differs from the third instar nymph in having proboscis reaching first abdominal segmen t, each thoracic segment with a pair of spines on dorsum, wing pads reaching fourth abdominal .segment, four dark greyish round spots at posterior margin of meso-thorax and two at posterior margin of meta-thorax, a rudimentary tenth segment at the end of abdomen". (PI. I, fig. 5).
Fifth instal.' nymph.-"Length of male 2.18 mm .• of female 2.28 mm. Greenish yellow with legs and abdomen bluish. Spines at anterior margin of head very minute, proboscis just reaching cOXa! of third pair of legs, prothorax with anterior margin convex, posterior concave, meso-thorax longest, wing pads reaching fourth or fifth abdominal segment, spines at tips of wing pads much reduced, greyish brown marks on the meso- and meta-thorax. as in the fourth instar, four greenish brown spines transversely arranged at posterior margins of segments three to eight. Rudiments of tenth segment become visible in the form of an anal tube" _ (PI. I. fig. 6).
4 COTTON JASSID IN THE PUNJAB
Symptoms of attack
Jassids cause injury to their hosts through sucking and desapping the plant. It is believed that jassids inject their toxic saliva into the plant tissue at the time of feeding and that this injection does more harm to the plant than the loss of sap. The effect of the toxic injection is to kill a small ring of tissue surrounding the puncture. This leads to uneven growth and the leaf becomes crinkled. The crinkling of the leaf lS a characteristic feature of jassid attack. In the early stages of the attack the leaf becomes yellowish or brown ish and as time goes on it assumes a cup-shaped appearance and slowly develops a characteristic brick red colour and is shed prematurely (PI. I, fig. 8).
PLATE I
Cotton jassid (EmpotUca devastans Dist.)
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Egg (x 23)
First instar nymph (x 28)
Second instar nymph (x 24)
Third instar nymph (x 29)
Fourth instar nymph (x 30)
Fifth instar nymph (x 22)
a. Adult-winter form (x 16)
b. Adult-summer form (x 16)
Fig. 8 ... Cotton leaf damaged by jassids
"' ...
('
;:;
7
4
5
5
CHAPTER III
EMPOASCA. SPECIES ON. THB COTTON PLANT'
The cotton plant is attacked by a large number of species of jassids in different parts of the world. In several countries the pest is very serious indeed. and the following list probably does not exhaust all the species which attack cotton in different countries.
TABLE I Empoasca species attacking cotton in different parts a/the world.*
Species
E. abrupta DeLong
E. benedettoi Paoli
E. bigutulla Mats
E. bipunctata
E. dolichi Paoli
E. d isti 11 guenda Paa Ii
E. dece piens Paol i
E. devastans Dist.
E. facialis Jac.
Country
U.S.A.
Italian Somaliland Tanganyika, Anglo-Egyptian Sudan
China, Manchuria, Formosa
Asiatic Russia
Transvaal, Belgian Congo
Transvaal, Belgian Congo
Egypt
Punjab N.W.F.P. Pakistan Sind Bombay Madras 1 Mysore Hyderabad (Deccan) Central Provinces (Bharat United Provinces j'
Bihar Delhi Central India
Italian Somali land Tanganyika Nigeria Belgian Congo Transvaal Rhodesia Nayasaland Kenya Anglo-Egyptian Sudan
Status
Not injurious
Injurious Not injurious
Injurious
Injurious
Not injurious
Not injurious
Not injurious
Very injurious Injurious Injurious Injurious Very injurious Injurious Injurious Injurious Injurious Inju fious Injurious Very inj urious
Injurious Injurious Injurious Injurious Injurious Very injurious Very inj u rious Very injurious Injurious
6 COTTON JASSlD IN THE PUNJAB
Species Country Status
---------~~--.-'-----------------------------
E. flavescens Fabr.
E. fabce Harris
E. formosana. Paoli
E. gossypii Paoli
E. herri var. motti Pr ....
E. libyca Berg.
E. minor Pro
E. maculata
E. tlot::!ta Melichar
E. punjabensis Pro
E. terra regince Paoli
Empoasca sp.
Empoasca sp.
Empoasca sp.
Empoasca sp.
Empoasca sp .
.,.
Philippines
South Carolina
Madras-Bharat
Haiti Brazil Sind-Pakistan Punjab-Pakistan Sudan
Punjab-Pakistan
Queensland
Bihar-Bharat
Punjab-Pakistan
Queensland
Fiji
Papua
Java
Peru
New Guinea
Injurious
Injurious
Not injurious
Injurious Not injurious Not iniurious Not injurious lnj u r ious
Not injurious
Injurious
Not injurious
Not injurious
Inju rious
Injurious
Injurious
Injurious
Injurious
Very inj urious
• Amplified from the table given by Afzal Husain and Lal (19+0).
It will be seen from Table I that some species which are injurious to the crop have not yet been identified. An interesting feature of this Table is that the same species may be injurious in one place and innocuous in another. The reason for this lies in the differences amongst the environmental conditions obtaining in various countries and the varieties of cotton gTC'wn in these places. That environment plays an important and hitherto little understood part in the life history of Empoasca sp. is also shown by the fact that Empoasca devasta71s multiplies enormously and becomes a menace to the cotton crop in the Punjab under humid conditions, while in Hyderabad (Deccan) it is a pest to be reckoned with when the weather is dry. Such examples could prohably be multiplied, and these prove the need of pursuing extensive and coordinated biD-climatic investigations on this insect.
7
CHAPTER IV
LIGHT TRAP COLLECTIONS OF JASSIDS
Collection of insects
An attempt was made to collect jassids by means of a light trap, and it is gratifying that a very large number of species were attracted to light. A light trap with 100 candle power filament electric bulb emitting white light at a height of four feet from ground level was put up once a week, every Tuesday, in an open place near the cotton fields of the Cotton Research Laboratory, Lyallpur, from the middle oOune, 1943, to the middle of June, 1944. The light trap was operated from dusk to dawn. All the insects collected were killed next morning, and the Empoasca spc:cies were separated out and counted (Ghani and Afzal, 1949).
Proportion of Empoasca devastans and other species
The total number of jassids collected and the proportion of Empoasca devastans in the collections is given in Table II.
TABLE n Light trap collection oj Empoasca species and the percentage oj E. devastans in it.
Date I Total No.
t Percentage 1 Date I Total No. \ Percentage of jassids ofE.D. of jassids ofE.D.
_________ ..... __ •• __ , 4~ ••• "_ . ~ ---- ---------~-
15-6-43 1048 5.3 27-10-43
I 8 I
22-6-43 565 11.3 4-11-43 a 29-6-43 663 15.2 10-11-43 1
6-7-43 7t8 7.1 17-11-43 4 ]3-7-43 1545 1.9 24-11-43 : 20-7-43 1185 3.5 to No jassids 27-7-43 628 4.6 29-3-44
3-8-43 3007 4,5 7-444 20 10-8-43 764 10.3 21-4-44 524 0.4 17-8-43 6149 52.1 25-4-44 146 0.7 24-8-43 691 36.9 3-5-44 474 0.2 31-8-43 ]897 2J.l 10-5-44 28 16-9-43 270 17.4 17-5-44 1084 0.6 22-9-43 1112 17.4 25-5-44 334 1.2 29-9-43 49 22.5 2-6-44 179 5.0 6-10-43 14 7.1 7-6-44 153 5.9
13-10-43 3 14-6-44 353 3.4 20-10-43 1
8 COTTON J ASSID IN THE PUNJAB
It will be observed from Table II that, at Lyallpur, jassids are abundant only during the six months from the end of April to the end of September. During the rest of the year very few specimens or none at all were attracted to the light trap. It is, however, known that jassids over-winter in the adult stage; but the number of insects which survives the cold weather must be very small and these also remain very inactive and concealed under places of shelter.
It will also be seen that specimens of E. devastans, which is the cotton jassid in the Punjab, were usually present in the catch except on the dates when very few jassids were caught. During August and September, however, a very high proportion of the jassid collection consisted of E. dev.lstans irrespective of the size of the catch. Thus during the season when this pest is most active on the cotton plant, the light trap offers a fairly effective means of attracting it. The utility of the light trap would, of course, be increased manifold if it were placed inside the cotton field.
Proportion of sexes in E. de'IJQstans collections
The specimens of E. devastans collected at each catch were sorted out according to the sexes, and the percentage of females is given in Table III.
Date
15-6-43
22-6-43
29-6-43
6-7-43
13-7.43
20-7-43
27-7-43
3-8-43
10·8-43
17-8-43
24-8-43
31-8-43
TABLE III
Percentage of females in the light tra p collections of E. devastans.
No. of \ Percentage Date E. D. of females
56 85.5 16-9-43
64 79.0 22-9.43
101 78.4 29-9-43
51 78.4 6-10· 43
30 96.7 21-4-44
41 73.0 25-4-44
29 72.0 3-5-44-
136 88.9 17-5-44
79 85.7 25-5-44
3203 82.7 2-6·44
255 66.4 7-6-44
401 71.3 14-6-44
No. of E.D.
Percentage of females
-----'----"-~""-"".""""~-"
153
193
11
1
2
1
1
7
4
9
9
12
67.6 1
67.6
45.5
71.4
75.0
55.6
77.S
75.0
LIGHT TRAP COLLECTIONS OF JASSroS 9
It will be seen from Table III that the number of E. deuastans females which were attracted to light was preponderately high throughout the year. The proportion of the two sexes in the field is almost 50 : 50, but the fact that by far the largest number of females was attracted to the light trap makes this method a fairly useful and effective measure of control. This is contrary to the experience of Wheeler (1937) in the Uni ted States who records that the males of Empoasca spp. (E. fabce Harr., E. erigeron DeLong, E. pergandi Gill., E. solana DeLong) far outnumbered the females in her light collections, though in the field the proportion of sexes was quite the reverse. It may be due to either the difference in species or environmental conditions, or both.
The phototropic response of E. devastans has not, so far as we are aware, been studied in detail before, and the present work has opened up a line of research which may be followed up with fruitful results. We have, for example, studied the reaction of insect to white light only, but it is quite possible, as has been found in the case of Aleurodidre (Deshpande, .1936, in India) and other insects (Burks et ai, 1938, and Marshal and Henton, 1938, in U.S.A.) that lights of different wave-lengths may have markedly different attractive capacity.
luff uence of weather conditions on the size of the catch
The number of jassids collected at the light trap was very fluctuating (cf. Table II), and the reason for this appears to be the variation in weather conditions during the previous week in general, and the night of collection in particular. Williams (1936) has recorded that bigger catches of nocturnal insects were made in Britain during dark and cloudy nights, the cloudy nights being associated with warmer conditions. Carruth and Kerr (1937) have observed in the U.S.A. tha~ light trap collections were appreciably influenced by night temperatures, and that the size of collection fell considerably when the minimum temperature sank below 6QoF. Afzal Husain et aI, (1934) studied the phototropic response of Platyedra gossypiella Saund. in the Punjab, and came to the conclusion that such response depended largely on temperature. They also found that moonlight affected the phototropic activity adversely. Sorensen (1939) found that Lygus hesperus Knight and Lygus elistis Van Duzee were attracted to light only on warm cloudy nights. Leach and Mullin (1942) have recorded that distinct peaks of activity of Aster leaf hoppers, as judged by the light trap collections, occurred during period of successive warm nights.
In order to elucidate the effect of environment on the light trap collections, the number of jassid caught during each night is set out against the minimum temperature during the night of collection, the rainfall, average relative humidity during the previous week and the phases of the moon in Table IV.
In order to elucidate the effect of various factors on the number of jassids caught. the figures of weekly catches in Table IV have been smoothed out by taking log (n+ 1) as suggested by Williams (1937). It will also be seen from Table IV
10 COTTON JASSID IN THE PUNJAB
TABLE IV
Jassid collection and environment.
1M
, . Rainfall (inch) I Average No. oJjassids collected InlmUm
relative Date tempera-
humidity Lunar ture -Dufing
Previous of previ- date Aclu 1 Log (n+l) cp. past 24
hours week aus week -----~---
1-~.30-' "-----------.:---
15.6·43 1048 3.0208 71.3 1.40 53.5 11 22-6-43 565 2.7528 81.1 ... . .. 50.1 ]8 29-6-43 663 2.8222 88.0 '" 0.38 53.9 25
6-7-43 718 2.8567 84.1 '" ... J
52.9 2 13-7-43 151-5 3.1892 73.4 1.72 1.78 66.1 9
20-7-43 1185 3.0741 79.9 ... ... 76.0 16 27-7-43 628 2.7987 79.1 0.15 1.75 80.1 23
3-8-43 3007 3.4782 83.0 '" 0.02 77.5 1 10-8-43 764 2.8837 81.9 ... 1.40 82.6 8 17-8-43 6149 3.7889 83.1 ...
'" 66.9 15
24-8-43 691 2.8401 82.1 ... ... 65.9 22 31·8-43 1897 3.2784 79.3 '" 0.89 66.7 29 16-9-43 270 2.4330 84.1 ... ... 66,3 15 22-9-43 1112 3.0465 81.9 ... \ 0 .. ~.6 67.3 21 29-9-43 49 1.6990 66.1 ... 56.3 28
6-10-43 14- 1.1761 65.1 f ... ... 54.6 6 13-10-43 3 0.6021 61.1 '" ... 58.0
I 13
20·]0.43 1 0.3010 58.7 ... ... 56.0 20 27-10.43 8 0.9542 54,4
'" ... 59.7 27 4-11-43 '" ... 57.1 ... ... 66.6 5
10-11-43 1 0.3010 52.8 '" ... 72.7 11 17-11-43* 4 0.6990 49.1. ... ... 69.9 18
7-4-44 20 1.3222 58.1 ... 2.69 81.1 I 13 21-4-44 524 2.7202 72.9 ... '" 48.6 27 25-4-44 146 2.1673 75.1 '" '" 51.3 1
3-5-44 474 2.6767 70.1 ... .. , 38.4 9 10·5.44 28 1.6424 73.1 0.02 0.02 38.1 16 17-5·44 1084 3.0354 72.4 ... 0.20 51,6 23 25-5-44- 334 2.5250 76.1
'" ... 35.6 2
2.6-44 179 2.2553 75.1 ... ... 31.8 10
7-6-44 153 2.1875 77.1 '" .. ,' 42.4 15
14·6,H 353 2.5490 I
76.3 '" 0.11 53.4 22
• No jasids were caught in the light trap between 24-11.43 and 29-3-44. Minimum temperature suring this penod varied between 38.1° and 55. 1°F and average relative humidity between 72%dnd 96.3%.
LIGHT TRAP COLLECTIONS OF JASSIDS 11
that very few figures of rainfall are available, and as the relative hutnidity is conditioned by the rainfall, the latter factor only is taken into consideration. It may also be mentioned that in the absence of self-recording meteorological instruments no continuous records of temperature or humidity are available. The figures given in Table IV are the routine figures available from the Pakistan Meteorological Department. The minimum temperature is the lowest temperature reached at any time during the night. Rainfall and relative humidity are recorded at 8.0 hours.
As a first step in the statistical examination of the figures given in Table IV, simple correlations were worked out. These are given below:
Catches and humidity : r= -0.5482 "Highly significant
Catches and min. temp.: r= + 0.9328 Highly significant
Both these correlations are significant up to 1% level, but an integrated effect
of both these factors on the catches can only be found out by working out the partial regressions, as it is only then that the actual effect of each factor Can be accurately assessed. The partial regressions were worked out and are given below:-
Partial regression coefficient between catches and humidity, keeping min. temp. as constant = + 0.1222 Non-significant
Partial regression coefficient between catches and mm. temp., keeping humidity as constant= +0.9037 Highly significant
It will be seen from the above that humidity plays very little part, and the catches were mainly influenced by the minimum temperature. It will also be seen from Table IV that very few jassids were caught on the nights when the minimum temperature fell below 70°F and largest catches were obtained when it ranged from 71° to 88°F. It would thus appear that the jassids prefer warm nights for their nocturnal activities.
It will also be seen from Table IV that it is \'ery difficult to separate the effect of moonlight from various other factors which influenced the size of the catch, as by the time the opposite phase of the moon appeared the weather conditions had changed to a considerable extent. Moreover, the observations were taken at weekly intervals. During this period both the phase of the moon and weather conditions changed and thus it became difficult to assess the effect of the two separately.
12
CHAPTER V
SPECIES OF EMPOASCA ATTACKING COTTON PLANT IN THE PUNJAB
Method of survey
In all the previous literature on cotton jassids, only E. devastans has been mentioned as the pest of the cotton plant in the Punjab. During the course of the present work, however, a few other specimens, hitherto unidentified, were usually found in the collection of jassids from cotton grown in different parts of the Province. From these specimens Dr. Pruthi (1940) described the following
three new species :-
(i) E. minor Pruthi.
(ii) E. kerri var. motti Pruthi.
(iii) E. punjabensis Pruthi.
In order, however, to find out the status of these insects as pests of cotton in different parts of the Province, a survey was carried out during 1940-42. (Abbas and Afza!, 1945). Fortnightly collections of jassids from the American cotton fields in different parts of the Province were made by means of a hand-net. An effort was made to catch about 300 jassids at each time. The actual number, however, varied with the season and place of collection.
Identification of species
An effort was made to identify the species with the help of the descriptions given by Pruthi (1940), but it was found that correct identification was only possible from an examination of the male genitalia (Pruthi, 1925). It is evident that identification by this method is a slow and laborious process, and it was not possible to examine each individual of the big collection received from all the places. A random sample of ten or twelve males from each catch of 1940 and 1941 was examined in detail and identified. As the sample examined was purely a random one, it was hoped that its identification would represent the composition of the whole sample.
SPECIES OF Empoasca ATTACKING COTTON PLANT IN THE PUNJAB 13
The species found io different places
The percentage of E. devastans in each case is given in Table V.
It will be seen from Table V that the percentage of E. devastans was low in the beginning of the season at some places in the Province, but it went on steadily increasing and at the end of the season it became the predominant species. It will, however, be noticed that in the south-western tract (Khanewal, Vihari and Arifwala), species other than E. devastans were in greater abundance than in the rest of the area surveyed.
The percentage of other species 10 the random samples IS given in Table VI.
It will be seen from Table VI that, of the three new species found in the collection, E. minor and E. kerri var. motti were most numerous. Only four specimens of E. punjabensis were found as against 190 of E. minor and 484 of E. kErri var. motti. This can only be explained by either presuming that E. ptlTljabeflSis is not a pest of cotton plant in the Punjab, and that the stray ind ividuals collected were only casual visitors; or that it may be a pest of the cotton plant, but that the population of this species is always very low. It has not been possible so far to prove or disprove either of these possibilities, but the fact that its population is so low as compared with that of other species is ample justification for not considering it further.
It will also be seen that while E. minor was the predominant species in Chiniot, Sargodha and Bhalwal, E. kerri var. motti dominated in the south-west of the Punjab. The reason for this will probably lie in the availability of the most favoured host plants of these species in the respective localities. It is unfortunate that information on the most preferred hosts is not available for E. minor. It may, however, be mentioned that the areas of its abundance are contiguous and possess similar soil and climatic conditions.
As regards E. kerri var. mottj it is known that it prefers guara (CyamopslS psoraljoides) to cotton. Guara is groNn in all places as a fodder crop and is used in some localities as a source of green mlnure. The attack of E. kerri var. motti on guara is usually very severe, and the pressure of population on this crop is perhaps responsible for its' overflow to cotton. When guara is used as a green manure, the luxuriantly growing standing crop is buried in the soil in July or August, and in this case the entire adult population transfers itself to some other host plant. From this it can be argued that the population of E. keni var. motti will be very much bigger on cotton fields situated near the
COTTON .TASSID IN nIE PUNJAB
TABLE
Percentage of Empoasca devastans Dist. in the jassid
JULY AUGUST
Localities F ortnight Fortnight
surveyed ~--I"--r==--~_~~I __ = ~~~ __ I_ ----~ \_~_=II----
1941 1940 11941 1942 1940 /1941 11942 1940 1941 1942
----.--- -_. ---" -------_ -- .------_ -_-- ___ ._ .. _--
Lyallpur .,. 100
Bucheki ··'1
SangIa Hill ...
Chiniot 82,6
Shah pur .•. 100
Sargodha
Bhalwal
Khanewal
Multan
Vihari
96.3
0.0
76.9
Montgomery 94.8
Arifwala .. 42.9
Nankanasahib ,100
Jhang .. ·1 ...
Chichawatni 1100 I
Hafizabad ... \93.8
Hansi (East I 94.1 Punjab) " ..
J
D. G. Khan)
69.5
100 100
97.9
100
100 100
71.7
95.6 96.2
100 100
96.9
31.8 100
100
100
94.5
96.3
1'6 50.8 96.3 68.0 98.7 27.8 93.3 94.1
90.9 92.3 41.9 94.1 97.6 37.7 100 96.4
0.9 2.3 0.0 1.0 0.9 2.0 1.0 20.7
50.0 22.7 27.3 98.2 70.5 50.0 97.4
25.0 1.8 57.1
82.1 14.S 1.4 50.0 13.0 100 97.6
33.3 40.0 87.5 12.5
100 100 90.8 100 92.9 100
33.3 69.2 i 25.0 50.0 75.0 49.3 67.7 90.0
25.8 65.0 4.8 82.4 71.4 84.1
95.5 91.8 100 94.2 89.5 94.3
100 SO.l 100" 92.0 92.7 94.7 99.3
100 0.0
SPECIES OF Empoasca. ATTACKING COTTON PLANT IN THI': PUNJAB 15
v
collection made from cotton during 194°-42.
SEPTEMBER OCTOBER ------1-------------
Fortnight Fortni,ght
I II I II
1940 r 194~~;11940 --1~41 i 1942 -1~~;11941 11942 - 1940 11941 1942 1--- ~-.. -.- -----. -~---i- --1- _.-._-... ,100 100 '" I 98.4 ... ... 94.8 1 ... ... 99.0 99.3
... 100 100 _.. 1100 100 .. _ leo 1100 '" LOO 100
... 96.0 I ••• ... 98.9 ... ... . ..• I ... 96.8 I I
95.7 ,100 ... I 90.9 92.9 ... 100 97.7 ... 1100
9~ ~ 1::
4 1
1
::.4 . 9;~0 9;.~ 9;·.~ 8;.~ 1::.3 99 .. 0 ::: I 8;.'3 9~~~ 99.0
91.0 94.1 95.1 87.2 95.0 98.5 '" 90.0 ... 92.7 1 97 .3 99.0
6.3 0.0 0.0 17.7 0.0 90.6 93.0 33.3 92.3 94.3 30.0 87.5
68.1 73.5 98.5 83.3 71.7 94.1 I 89.0 90.6 99.5 84.0
76.4
83.3
92.1 99.1
55.6 80.0
88.9 97.9
98.5 91.7 92.9
90.9 91.7
52.9 93.4
92.9
75.0
98.6
27.8 67.7
85.7 100
82.1
50.0
98.3
85.7
... 100
96.3 90.0 74.0 91.5 9j.5
92.8 72.2
90.6 96.2
95.4 73.3
95.1
97.3 100 98.6 96.9 98.3 98.6 92.7 92.3 99.6
0.0 66.7
98,4
33.3
88.6 100
93.2
95.1 94.5
75.7 99.2
... \ ...
16 COTTON JASSID IN THE PUNJAB
TABLE
Proportion of different species of jassids collected
I JULY AUGUST .__..__-~--------.. --'- --- ---_----
Fortnight Fortnight
Localities ~~-----.--~ - -- --- ,_ .. _- -------~- -_--_------_ .. --
surveyed I II I II:
E.MIE.K E. P. E.M. r;.K.1 E.P.
-----.. _----I I
E.M. E.K. E.P. E.M E.K. E. P.
--_. __ ... _-- -I-- _----- -_ -------1-----.. _ .. · -----_._
Lyallpur 0 0 0 0 0 0 1 I 3 0 0 11 0
Chiniot 2 0 0 2
I 0 0
Jhang 3 7 0 6 8 0 9 6 0
Chichawatni 3 8 0 3 9 0 1 0 0
.Montgomery 3 0 0 0 22 0 0 9 0
Arifwala 0 2 0 0 6 0 1
Multan ... 1 0 4 0 2 4 0 2 19 0 20 0
Vihari 0 12 0 0 9 0 0 10 0
::: 11~·· Khanewal 0 0 10 13 0 2 20 0 0 25 0
Sargodha I· .. 2 4 0 7 0 0 8 4- 0
Bhalwal 16 2 0 10 0 0
Hafizabad I 0 0 1 ... I
I Hansi (East 0 0 1 7 1 () 6 11 0
Punja b)
_. - _.'- -- - --1- --- -- ----
I T ota] 1 f) 6 1 20 48 1 46 99 0 35 96 0
I E.M.=Empoasca minor Pruthi. E.K. = Empoasca kerri var.
SPECIES OF Empoasca ATTACKING COTTON PLANT IN TlIE PUNJAB 17
VI
from cotton during 1940 and 1941.'
SEPTEMBER OCTOBER _.' ,----,-~.--------
Fortnight Fortnight -----"-,~-,-,-,,-"~~--'-- --------,---------
I 11 I II --- - --- ~--I ---- -......,- --- , --
E.M. E.K. \ E.P. E.M. E.K. \ E.P. E.M.· E.K.! E.P. E.M.I E.K. E.P. --1------ -----1- ------------ _- -----...... 1 ... 1 ... "'1'" 130020
: : I: : ~ I: 6 7 o 2 o o
: 1: o o
2
2 1 o 2 o
2 o 2 o 8 o
0 9 () 0 3 0 0 2 0
1 23 0 0 20 () 4 13 0 1 6 0
1 4 0 1 2 0 1 11 0 1 6 0
1 11 0 0 12 0 4 17 0 3 IS 0
0 1 0 9 3 0 10 3 0
2 1 0 8 4 1 2 1 0
1 2 1 1 3 0 0 1 0
0 2 0 1 0 0 3 16 0 0 7 0
~ _,_~! ___ I_I __ I ____ ,_1 ___
11 64 11 24 153 1 1 29 In 0 8 45 0
I I I I
motti Pruthi . E.P.=EmpoCLsca punjabensis Pruthi.
18 COTTON JASSID IN THE PUNJAB
guara crop than on those far away from it. That this IS so is proved by the figures given in Table VII.
TABLE VII Percentage of species other than E. devastans on two fields of cotton.
______ ~-____ 11si_~~~14~ ~~Ug~ls:!~ September October ~114th _ __ ~I_ 14th
Cotton field contiguous to guara field .. I nil nil 2.2 82.0
Cotton field I t mile away from guara fidd nil nil nil 68.2
0.8 nil nil nil
nil 1.6 5.2 I 1.0
In this particular experiment, guara was buried between the first and the second date of sampling in August, and the preponderance of species other than E. devastans during this period can be explained by the invasion of cotton fields by E. kerri var. motti due to the absence of its favourite host. It will, of course, naturally be expected that cotton fields near the guara crop will harbour a much larger number of this species than those further away from it. Guara as a green manure is grown to a great extent in Montgomery and Khanewal, and this may explain the comparative abundance of this species on cotton in these localities (cf. Table V[).
The abrupt fall in the population on cotton of E. kerri var. motti in September can be explained from the figures given in Table VIII which show that E. herri var. motti cannot lay eggs freely on cotton, though the nymphs can feed on it and reach maturity.
TABLE VIII
Oviposition and feeding of E. devastans and E. kerri var. motti on guara and cotton.
o V!POS! !On F d' ee mg ---N o. -;;r---I,rO:-or No.or--N o. 0"[
Species Host plant females nymphs nymphs adults liberated hatched liberated emerged
-E~evastans -Ouara--- -72----- --nil "--1-5-... 150
E. devastans ... Cotton 72 46 150 80 E. kerri var. motti .. Guara 72 269 165 81 E. kerri var. motti ... Cotton 72 3 150 71
In this experiment the usual precautions of sleeving the leaves long before starting the experiments to prevent previous oviposition were carefully observed.
The figures in Table VIII provide an explanation of the phenomenon of the al:5rupt fall in the number of E. kerri var. motti on cotton in September. Although a very large number of adults of this species invade the cotton crop after the removal of guara, these adults soon die out and as very few eggs are laid this species practically disappears from the cotton fields after some time, viz., the beginning of September.
CHAPTER VI
ST A TUS OF DAMAGE DONE BY THE VARIOUS SPECIES OF EMPOASCA TO THE COTTON PLANT
19
The effect of jassid attack on the cotton plant has not so far been thoroughly studied by other workers. The only references on this point are couched in general terms. Parnell (1925.26) has pointed out from South Africa that (I with the reddening of the plant, development ceases, squares and very young bolls are shed, partly developed bolls dry up and only those that are nearing maturity ripen off and open naturally. A certain proportion of the latter always produces weak lint due to their development having been arrested at too early a stage." Sloan (1938) has mentioned the retardation of plant development and shedding of buds and young bolls as the after-effects of jassid attack in Queensland. Also that the" immature bolls develop poorly and produce wasty lint ......... ln a mild outbreak ......... the quality of lint is not as good as that from uninfested plants." Smith (1926) made a comprehensive study of the feeding habits of Hemiptera in U.S.A. and has given a detailed account of jassid injury to potato. He says that the appearance of a white spot round each puncture is the typical symptom of jassid feeding. A cross section of the leaf through the white spot shows a clear-cut area due to the destruction of chlorophyll probably by the Eali vary secretion of the insect. Afzal Husain and Lal (1940) are of the opinion that the harm clone to the plant by desapping through sucking is probably insignificant as compared to the injury done by injecting harmful toxic substances into the plant tissue. Ramiah (1944-45) has estimated the damage done to the susceptible varieties by jassids and he has stated that under the same conditions the resistant plants produced three times as many bolls as the susceptible ones. It is, however, important that the damage done should be accurately known as it is only then that the status of this insect as a major pest can be established.
Since there are three species of Empoasca, which are commonly found on the cotton plant in the Punjab, work on this problem was contemplated on all the three. It was, however, impossible to identify living specimens of E. minor ar.d to collect them in large numbers. Work on this insect could, therefore, not be pursued at all.
20 COTTON JASStD IN THE PUNJAB
Damage done to the plant by E. herri var. motti
This species could be collected in a pure state in large numbers from fields of guara. Cotton plants were grown inside jassid proof cages and a very high degree of infestation of E. kerri var. motti was maintained on them throu~hout the growing season. It was noticed that in spite of this high infestation, the plants continued to grow and develop normally and the characteristic symptoms of jassid attack i.e., the crinkling and reddening of leaves did not appear. There was apparently no difference between the plants growing in the "infested" and the "free" cage. Although no data on loss in yield or deterioration in quality of lint IS available, it is certain that such losses could not have been high. The insect failed to affect the vegetative organs of the plants and it is, therefore, extremely likely that the yield and lint also remained unaffected. E. kerri var. motti cannot, therefore, be considered as a serious pest of cotton in the Punjab.
Damage done to the plant by E. devastans
Amongst the cotton jassids, E. devastans is the only species which is a major pest of cotton and, therefore, a great deal of detailed work was done on this species (Afzal et ai, 1943).
The study was carried out in jassid proof cages and as the size of the cages was limited, only a small number of plants could be dealt with in the brginning. Later, however, bigger cageS were employed and a larger number of plants and varieties came under experiment.
During 1938 and 1939 only two cages, each measuring 6'" 6' x 6' were used. In the first year, six plants of a highly susceptible variety, namely, 38F, were grown in each cage and during the next year a highly resistant variety, 289F /43, was raised~ During both these years, the plants in one cage were kept free of any insect while in the other a high degree of jassid infestation was maintained by liberating a large number of adults of E. deuastans collected from bhindi plants. It is unfortunate that a census of this population could not be taken, but it should be noted that the population in the .• infested" cage was kept markedly high; as high as could be expected in nature in any year. In 1940, the experiment was repeated us.ing two susceptible varieties (38F and 289 F/K. 25) and two resistant varieties (289 F(43 and L.S.S.). Four plants of each variety were kept free of jassid while 20 plants of each were grown in a big cage (16' x 16' >< 8') under conditions of severe infestation. The general pl~n of the experiment is given in Table IX.
-
STATUS'Of DAMAGE 21
TABLE IX
Plan of the experiment.
I No. of plants grown Year
I. Variety Nature of the Jassid-free Highly infested
variety cage cage 1938 38F ... Susceptible . .. 6 6 1939 289F/43 ... Resistant .. , ·4 4 1940 38F ...
I Susceptible
'" 4 21 289F/K. 25 ... Susceptible ... 4 22 289F/43 ... I
Resistant ... 4- 21 L.S.S. ... Resistant ... 4 20
Sowing was done at the optimum time (end of May) each year and all cultural operations in both the cages were identicaL In the jassid-free cage care· was taken so that not a single insect found its way into it, while in the other cage a population of 200-300 nymphs per plant was maintained from the middle of July to the beginning of October.
Records of weekly growth in height and flower and boll production are available for 1938 and 1939 only, but the technological properties of the lint of all plants were determined throughout the course of the experiment.
(i) Growth in height
The height of the plants was measured from O-Node each week and the relative rate of growth was found by applying the equation H=Aebt (Afzal and lyer, 1934).
It was seen that the relative rate of growth of plants, (b), in the infested cage was significantly lower in the susceptible variety (38F) as compared to the plants in the jassid-free cage, while this difference in the case of the resistant variety (289F/43) was insignificant. This means that the heavy jassid infestation retarded the rate of growth in the naturally susceptible variety while it had no such effect when a naturally resistant variety was under experiment.
(ii) Flower and boll production
Flower and boll counting was done on all the plants daily and the records are summarized in Table X.
The figures given in Table X show clearly that the number of flowers and bolls produced on the plants kept free of jassid attack was statistically higher than those on the infested plants. in the case of the naturally susceptible variety. In the case of the resistant variety, on the other hand, although there was a reduction in the number of bolls in the infested plants, this reduction was non-significant. So far as shedding percentage, average weight of seed-cotton per boll and ginning Duttura are concerned, there was no difference between
22 COTTON JASSID IN THE PUNJAB
"" ~ o 0 o 0 -+
c_~ _____ c ______ ~ __ ~
lD ..r 0'1 N N If) N ~oo
c5 u., .....-I [""00 1""""i
N ,..... N +
o o '"'
o ~ ...... ......
__ c ______________ ·_c _______ ~ __ ~_~ __ ____:__I ---==--0; .r,
N .r, .... ......
o o czi
.r, r-. N + U1 "! o +
o o:--i
N N o o
-------------~-;e ..r o \0
U1 ..,.; *
__ c __ •• __ cc ____ •• _~ __________________________ _
~~ ~:gl ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ f;; ~ ~ ~ ~ >o~~ N N .... ~ ..,.; ..,.; N N o:--i N ..,.; N "" o:--i 0 0
<: -"I ~ I
].e ~ ~I :2 cJ)"'d~ctt 00
0.
o -+ '"'
..., C . '" 0 p::Z ~I .r,
o o co
o ."j ['-
--------.--.-
..r ______ -'---________ ~ ____________ c __
c '" '" ::g
o N
~ I
----------..... lD
"" ~ ~ .
STATUS OF DAMAGE 23
the" infested" and the" free" plants in both the resistant and the susceptible varieties. The total amount of seed-cotton per plant was, however, significantly more in the "free" plants as compared to the "infested" ones in the case of the susceptible variety, while there was no such difference in the case of the resistant variety.
(iii) Technological properties of lint The produce collected from the individual plants grown in 1938 and 1939
was examined for technological properties. In 1940. as a large number of samples was available from the infested cages, lots were drawn and six single plan1s were selected at random, from each of the six varieties. All these samples were tested for the following fibre characters :-
(a) Mean fibre length; (b) Modal length of fibres; (c) Fibre length irregularity (per cent) ; (d) Mean fibre weight per unit length; (e) Percentage of mature fibres; and (f) Highest standard warp counts (calculated).
The determination of the first four characters was done according to the method described by Ahmad (1933). The percentage of mature fibres was determined according to the standard method used in Pakistan (Gulati and Ahmad, 1935) using the new device for mounting the fibres (Ahmad and Gulati, 1936). The highest standard warp counts were calculated according to the prediction formula of Ahmad (1941).
As the samples were too small for an actual spinning test, the calculated value of highest standard warp counts has been used in the present case to represent ~he expected performance of the samples in a spinning mill.
The details of these six characters as determined per plant are given 10
Table XI.
The statistical interpretation of the data given in Table XI by the "Students" ,t' method (Fisher, 1932) is given in Table XII.
A consideration of Table XII will reveal that in the case of the susceptible variety (3SF) the mean and modal length and the fibre irregularity were significantly higher in the jassid free plants as compared to the infested ones. There was, however, no significant difference between the free and the infested plants in the case of fibre weight and the percentage of mature fibres. As the calculated value of the highest standard warp counts was significantly higher in the case of jassid free plants than th(lt ofthe infested ones, it may be inferred that the lint samples from the "free" cage were better than the samples from the "infested" cage. A repetition of this experiment in 1940 gave similar results and it may, therefore. be concluded that jassid attack leads to a definite deterioration of lint quality in this cotton.
1940 P-A 289F/K.2S 1 ,., 2
1940 P-A 289Fj43
1940 P-A L.S.S.
3 4
1 2
~I
1 2 3 4
2.12 2.24-2.43 2.30
2.40 2.37 2.22 2.24
2.28 2.34 2.20 2.17
2.25 2..48 2.80 2.61
2.74 2.71 2.47 2.30
2.60 2.61 2.44 2.37
23.9 26.4-26.5 21.6
29.S 25.2 26.7 21.9
25.0 22.7 25.6 22.6
1.71 1.67 1.73 1.55
1.37 1.66 1.85 1.43
1.50 1.69 1.18 1.52
58 49 53 43
34 47 46 39
47 53 13 35
XI of injested and free plants.
I ,
H.S.W.e. i Plant calculated I No.
44.1 39.9 44.8 42.3 40.7 40.4
1 2 3
I 4-
~ I 45.0 1 41.3 2 43.7 3 38.3 4
321 33.7 34.6 33.2
31.9 35.0 40.1 37.3
42.3 3ts.9 32.2 37.0
37.3 37.7 37.0 33.8
2 3 6
13 18 21
2 9
12 13 15 22
3 5 6
15 19 23
1 2 5
16 19 20
Mean fihre length (em.)
2.30 2.34 2.19 2.35 2.39 2.30
2.53 2.42 2.37 2.54
2.15 2.12 1.89 2.11 2.11 1.97
2.20 1.97 2.09 2.02 2.22 1.89
2.49 2.53 2.40 2.42 2.50 2.11
2.18 2.28 2.20 2.37 2.04-2.27
STATUS OF DAMAGE 25
INFESTED CAGE
Modal length (coo.)
Fibre iMean fibr)p length j'weight per' ercenft- H S W C irregu- ,unit length! age 0 ..•. larity 1 10- 6 gm., I mature calculated
(per cent) i em. I fibres
--i:~£--- ~~:~---Il:~ I :i- ~~~ 2.37 25.4 I 1.30. II 41 36.5 2.62 24.1 1.53 49 39.9 2.72 24.7 1.69 66 40.1 2.66 25.5 1.54 41 37.7
2.88 2.70 2.60 2.75
I 2.19 2.22 1.87 2.21 2.22 1.92
2.46 2.09 2.25 2.14 2.45 1.89
2.77 2.83 2.66 2.69 2.85 2.21
2.40 2.52 2.38 2.62 2.22 2.56
22.5 24.9 20.1 18.6
22.9 23.7 18.4-23.0 23.4-15.8
237 16.1 '27.7 26.6 23.9 16.4
22.7 26.3 25-.7 26.9 26.0 21.5
19.9 19.3
1
18.0
I 20.3 13.7 23.6
1.99 1.55 1.47 1.64
1.62 1.56 1.46 1.77 1.71 1.67
1.90 1.93 1.36 1.43 1.52 1.20
1.62 1.66 1.87 1.77 1.84-1.78
1.73 1.90 2.08 l.62 1.82 l.63
I ! I
71 52 49 59
43 36 39 55 47 67
55 44-26 26 4-8 6
52 45 57 58 66 49
55 79 69 56 Sl 42
413 41.9 41.0 44.7
32.1 31.9 26.7 30.3 30.4 285
31.5 22.7 33.2 28.8 36.5 :26.0
42.9 43.5 37.8 39.7 41.9 31.6
33.1 35.6 30.4-39.9 27.S 35.5
26 COTTON JASSlD IN THE PUNJAB
TABLE
Statistical interpretation of the
Infested cage Control cage
Variety Fibre character No. of! A No. ofl Average sam- verage sam- 1 1 value 1 va ue p es pes
1 2 3 4 5 6 _-.-_.-- _._._--_ .. ,._--_._-- '.-
P-A 38F
P-A 289FI K. 25
Mean fibre length (cm.) Modal length (cm.) Fibre-length irregularity (per cent) Mean fibre weight per unit (10- 6 gm./cm.)
Percentage of mature fibres Highest standard warp
(calculated)
Mean fibre length (em.) Modal length (cm.)
length
counts
Fibre-length irregularity (per cent) Mean fibre weight per unit length
(10-6 grn./cm.) Percentage of mature fibres Hig hest standard warp counts
(calculated)
P·A 289F/43 Meiln fibre length (em.) Modal length (em.) ... Fibre-length irregularity (per cent) Mean fibre weight per unit length (10- 6 gm./cm.)
Percentage of mature fibres Highest standard warp counts
(calculated)
P-A L.S.S. Mean fibre length (cm.) Modal length (cm.) '"
j Fibre-length irregularity (per cent) Mean fibre weight per unit length
(10- 6 gm.Jcm.) Percentage of mature fibres Highest standard warp counts (calculated)
• Indicates significance at 5 per cent level. t Indicates significance at 1 per cent level.
6 6 6
6 6
6
4 4 4
4 4
4
2.31 2.61
24.6
1.58 49.9
38.1
2.46 2.73
21.5
1.66 57.7
42.2
6 6 6
6 6
6
4 4 4
4 4
4
1938 2.44 2.79
21.8
1.59 50.3
42.0
1939 2.44 2.66
20.5
1.56 47.2
42.1
XII
technologicd! properties.
Difference in
average D.F. 't' values
(col. 4-col. 6) I
7 8 9 --- .~-.. -~"----~--
- 0.13 .1 - 0.18 + 2.8
- 0.01 -- 0.4
- 3.9
10 1\ 2.825* 10 2.370<: 10 I 4.070t
10 0.137 10 0.060
10 i3.488t
STATUS OF DAMAGE 27
Infested cage Control cage Differ-ence in
N fi N f' average D.F. o. 0 Average o. 0 Average values
saJm- value sa1m- value (col. lI-p e5 1 p es col. 13) 10 11 12 ]3 14
6 6 6
6 6
6
2.06 2.10
21.2
1.63 47.8
30.0
4 4 4
4 4-
4
6 1 2.06 I 4 6 2.21 4 6 22.1 4
6 6
6
1.56
1
34.2
29.8
4 4
4
1940
I 2.18 - 0.13 2.34 - 0.24
24.1 - 2.9
1.82 71.7
1 33.4
1940
- 0.19 -23.9
- 3.4
2.27 1- 0.21 2.53 - 0.32
24.6 - 2.5
1.66 50.8
36.1
1940
- 0.11 -16.6
- 6.3
15 ! 8 8 8
8 8
s
16
2.052 2.318* 1.589
2.094 3.393t
3.014*
8 \ 2.480* 8 2.217 8 0.980
8 8'
j 8
0.700 1:728
2.169
+ 0.02 + 0.07 + 1.0
0.381 I 6 0.829 \ 6 0.445 6
2.41 2.67
24.8
4 4 4
2.31 + 0.10 2.55 + 0.12
25.9 - 1.1
8' I 1.164-8, .\ 0.775 8 0.612
+ 0.10 +10.5
+ 0.1
...
... ...
.. ,
.. ,
...
I '" ... . .. '" ...
...
0.865 1.390
0.088
...
...
...
., .
...
'"
I
I
6 6
6
6 6 6
6 6
6
1.76 54.5
39.6
2.22 2.45
19.1
1.80 58.7
I 33.7
4 4
4-
4 4-4
4-4-
4
1.58 41.5
37.6
1940 2.25 2.50
24.0
1.47 37.0
36.4
+ 0.18 8
[+13.0 I 8
+ 2.0 8
- 0.024 8 - 0.05 8 - 4.8 8
+ 0.32 8 +21.7 8
- 2.8 8
. 1.780 2.882*
0.699
0.372 0.625 2.740*
2.633* 2.236
1.192
28 COlTON JASSID IN THE PUNJAB
The results of 1940 with another susceptible variety, 289F/K. 25, gave similar results although the 't' test was in some cases lower than the 5% level of significance. The trend of values is, however, quite obvious and a general conclusion that fibre quality suffered with jassid attack in the case of naturally susceptible varieties seems justified.
Dealing with naturally resistant varieties, 289Fj43 grown during 1939 and 1940 and L. S. S. during 1940 only, it seems that. in general, there was no significant difference in values of the different fibre characters. On the contrary a slight improvement was noticed in a few characters. It is, however, believed that no improvement in quality as a result of jassid attack- could be expected under the general agricultural conditions.
The cotton jassld of the Punjab and its effect on the plant
It will be clear from the foregoing that E. devastans is the only species of jassids which is responsible for causing damage to the plant and bringing about a reduction in the number of bolls and a deterioration in its lint quality. Further consideration will. therefore. be exclusively devoted to this species.
The differential response of the resistant and the susceptible varieties has not so far been recorded anywhere else. The resistant varieties when highly infested showed in a fairly pronounced manner the typical symptoms of jassid attack and the drain on the cell sap must have been quite appreciable. These varieties were, however, able to tolerate this drain much better than the susceptible ones as the latter, when subjected to a heavy jassid attack, suffered both in plant growth and fibre qualities. It has always been stressed in the Punjab that no variety of American cotton should be grown in areas where the jassid attack is liable to be serious, unless it was resistant to such an attack. The present investigations have further proved the soundness of this recommendation. In certain years jassids are present in very large numbers in tracts which are exclusively devoted to the cultivation of resistant varieties and fears have sometime been expressed that these varieties although resistant under normal conditions. may suffer a set-back in years of heavy attack. The available evidence points out that there is no room for such fears.
29
CHAPTER VII
HOST PLANTS AND SEASONAL HISTORY OF E. DEVASTANS
After having determined the most important species of jassids attacking the cotton plant and responsible for severe losses to this crop. an extensive study ofits alternate host plants was found necessary. It was considered that this study might lead to important information about the habits of this insect which might ultimately be useful in devising measures of control.
Bhatia (1932) has mentioned the following host plants in the Pu.njab :
Rhindl (Hibiscus esculentus). hollyhock (Althcea rosea), potatoes (Solanum tuherosum). brinjal (Solanum melongena), castor (Ricinus communis) and artichoke (C)'nara scolymus). He also collected a few adults from sem (Dolichos lablab) and kali tori (Luffa mgyptiaca) but has made a note that this insect did not breed on these two plants. Cherian and Kylasam (1938) have in addition to the above plants also mentioned sunflower (H elianthus annus) as a food plant of E. devastans in Madra<; (Bharat), Rajani (19-1-0) reported bhindi, brinjal, potato, falsa (Grewia asiatica) and kangi buti (Abutilon indicum1 from Sind. Afzal Husain and Lal (194J) have finally listed the follOWIng plants as altern1te hosts in the Punjab :-Hollyhock. castor, brinjal, potato, bhindi. ban kapas (Hibiscus vitifolius), SUlI kukra (Hibiscus cannabinus) and some cucurbits.
It has been seen that all previous workers have taken the mere presence of adults, in however sma!! a number. on a particular plant as an indication of that plant being an alternate host. This m~thod of recording host plants is. in our opinion, not accurate. To call a puticular planta host plant, evidence must be forthcoming that the insect can feed and bre~d on it. This ffi!thod was followed during the course of the present investigation.
Preliminary investigations
During 1938-40 the incidence of E. devastans on four alternate host plants (bhindi, brinjal. potato and hollyhock) was studied by counting the living nymphs on a large number of plants. As far as possible all leaves on a plant were examined every morning. The nymphal population per plant as determined by the above method is given in Table XIII.
It will be seen from Table XIII that of the four host plants studied, , bhindi was the most favoured. The other three plants, though not so important
during the summer months. appear to provide food and shelter during the cold \~
weather and help the insect to tide over the winter.
30 COTTON JASSlD IN THE PUNJAB
TABLE XIII
Nymphal population of E. devastans on different host plants
Bhindi Brinjal Potato Hollyhock Months Fortnights --- -_.
1938 1939 1938 1939 1938 1939 1938 1939
-I --- --- -_- --- ---- -- ----April J 0.4 0.2 0.4 9.7 ... ... '" ... ...
II 0.5 0.4 0.5 1.6 .. '" 0.7 1.8
May .0. J 3.0 2.8 9.4 4.0 '" 1.9 ... ... n 3.9 3.2 1.4 3.8 ... 1.0 ... ...
June '0. I 17.2 18.2 0.3 4.0 ... ... ... . .. II 37.4 27.8 0.9 0.8 ... ... ... . ..
July '0' J 81.6 63.8 0.7 0.7 .. ' ... ... . .. II 135.2 76.7 0.7 ... ... " . .. ...
August '"
I 65.7 133.5 0.3 1.4- .. , ... . .. ... II 84.3 73.3 0.4 0.7 ... ... ... ...
September ... J 36.5 75.4 0.6 0.3 ... . .. ... ... II 19.3 49.6 0.4- .. , ... ... .. . . ..
October ... J 9.3 45.9 1.4 1.7 ... ... ... I . .. II 13.5 11.9 5.1 0.6 0.2 0.3 .. , ...
November ... J I 13.2 15.6 7.4 0.9 1.4 0.8 0.8 4.1 II 21.1 I 33.5 15.1 3.9 3.3 1.4 ... 5.6
December ... I ... 155.6 14.3 3.3 5.6 2.2 0.4 6.1 If 5.0 61.5 5.3 2.9 2.4 3.4 0.6 7.5
January ... J 5.0 6.8 1.4 1.4 1.1 2.0 0.5 3.6 II ... ... 0.1 0.6 1.1 1.0 0.1 1.7
February ... I . .. 1.7 0.3 I 0.4 0.4 ],0 ],0 0.5 II ... ... I 0.6
I
1.3 0.4 0.1 0.1 0.1
March ... I
I
0.7 I 2.1 0.6 0.5 0.1 0.3 -.. ...
I II ... . .. 0.8 3.6
I ... 0.5 0.1. ...
Range of host plants For a detailed study of the host plants of E. devastans, adults and nymphs
of this insect were collected from bhindi and were liberated about once a week during June and July, 1943, on twenty-one different species of plants (Ghani, 1946). The number of eggs laid by 12 females and the number of adults developed from 20 nymphs are given in Table XIV.
HOST PLANTS AND SEASONAL HISTORY OF e. deva.stans 31
TABLE XIV Oviposition and nymphal development of E. devastans on different plants.
No. of eggs No. of adults
Name of plant laid per formed from 12 females 20 nymphs
--.. --"-~---
Lagena-ria vulgaris (Kadu) 0.36 0.0
Luffa cegyptiaca (Kali tori) 2.57 0.0
Citrullus vulgaris var. fistulosus (Tinda) 0.08 0.0
Cucurbita maxima (Halwa kadu) 1.85 0.09
Solanum lycopersicum (Tomato)* 2.25 0.0
M omordica charantia (Karela) 0.80 0.0
Cyamopsis psoralioides (Guara) 0.50 0.07
Vitis vinifera (Grape vine) 0.0 0.06
Grewia asiatica (Falsa) 0.0 0.50
Althma rosea (Hollyhock)t 4.63 4.75
Zinnia sp. 0.0 0.0
H elianthus annus (Sunflower) 1.47 1.87
Datura Jastuosa (Datura) 0.25 0.75
Hibiscus esculentus (Bhindi) 66.67 17.00
Hibiscus rosasinensis (Gurhal) 2.05 0.0
Hibiscus mutabilis (Changeable rose) 4.67 1.07
Hibiscus tiliaceus 1.00 1.13
Hibiscus vitifolius (Ban kapas) 0.0 0.0
Ricinus communis (Castor) 0.0 1.00
Solanum tuberosum (Potato)* 4.00 1.50
Solanum melongena (Brinjal) 4.50 4.30
*Boch summer dlld wlnr~r crops. "tWinrer crop.
The figures given in Table XIV are very interesting. On some plants the insect could not lay eggs, but the nymphs could feed and reach maturity.
32 COTTON JASSID IN THE PUNJAB
S.ince, m nature, the young nymphs of E. devastans are not very mobile, this category of plants could not be said to be host plants. The migration of advanced stage nymphs to such plants will be of little consequence as these will soon reach maturity and will not be able to la.y eggs. In a different category are plants where eggs could be laid. but the nymphs emerging from these could not feed on the plant and would soon die out. Obviously such plants should also be ruled out as host plants. In the case of two plants (ban
kapas and Zinnia) there was neither egg-laying nor could the nymphs feed on them. Such plants could certainly not act as host plants.
It is well known in the Punjab that bhindi is the most favoured host plant of E. devastans, while cotton comes next in order.
In the light of these experiments. it is now possible to revise the list of alternate host plants of E. devastans in the Punjab.
The plants are given below in order of their importance from the jassid breeding point of view.
1.' Hibiscus esculentus (Bhindi) 2. Althma rosca (Hollyhock.)
3. Solanum melongena (Brinjal) 4. Sola.num tuherosurn (Potato) 5. Hibiscus mutabilis (Changeable rose) 6. Hibiscus tiliaceus 7. Helianthus annus (Sunflower) 8. Datura fastuosa (Datura)
Seasonal history
Of the above alternate host plants detailed studies of nymphal population throughout the year was carried out on the following five most important host plants of E. devastans. The results are depicted graphically in Fig. 1 (Abbas, 1943).
It is obvious from Fig. 1, that from June to August the insect is most active on bhindi and during August and September on cotton. Thereafter, it begins to diminish rapidly, till it becomes very insignificant on cotton in
November and on bhindi in January. From November, it begins to migrate and breed on potato and hollyhock but more so on brinjal, where it continues till January. During February to April, the species i-s at its lowest and just pulling through on hrinjal, potato and holly hock.
It will be clear from the above account that a close season for cotton and a clean-up campaign, in order to control this pest, will not be a practical proposition because some of the alternate host plants. potato, bhindi and brinjal, are of great economic importance and their cultivation cannot be prohibited.
- BHINOI
COTTON
BRINJAL
POTATO
HOLLYHOCK
Fig. l.----Seasonal history of Empoasca devasfans Dist.
33
CHAPTER VIII
POPULATION OF E. DEVASTANS ON THE COTTON PLANT IN THB PUNJAB
The ultima1e ill-effects of jassid attack on the cotton plant depend on two factors, namely, the number of insects which attack the plant and the power of resistance of the plant to a particular intensity of attack. An accurate method of estimating the population is very desirable, but it is realized that it is a very difficult undertaking as both the nymphs and the adults feed on the plant and therefore cause injury. The nymphs are closely attached to the leaves and the adults ate very agile. The method of census should, however, take into account
both the nymphs and the adults. While suitable methods have been devised for estimating the population, the injury done to the plant by different levels of population has not so far been determined.
It bas already been shown that even a very heavy attack of E. devastans on a naturally resistant variety does not do much harm. In the same way, it could probably be argued that a sufficiently low intensity of attack would not do much damage even to a naturally susceptible variety. This means that for every variety there would be a floor-level of attack below which no harm comes to the plant. Such floor-levels of attack for different varietles have not so far been determined. This aspect of economic entomology is really very difficult to sol ve, as the production of consecutive, satisfactory insect populations in test plots is not an easy matter. For this purpose a detailed knowledge of the life history and physiology of the insect is necessary. For plant-breeding work, however, that infestation is best which gives the maximum difference between the resistant and the susceptible plants (Painter, 1943).
It is, however, seen in nature that under an identical set of environmental conditions, one variety is attacked much more than another and the variety which shows a lower population is termed as more resistant than the other which harbours a larger population.
Method of estimating the population The search for a suitable method of estimating the population was started
in 1937 (Verma and Afzal, 1940). The following three methods were used for taking the census of population in American varietal test plots laid out according to Fisher's randomized block system at the Cotton Research Farm, Risalewala, during 1937-43. There were five to seven blocks of varieties in different seasons and as the population was determined for each sub-plot, the data were amenable to statistical treatment.
(i) Sweeping.-This was done with a hand-net, thirteen inches in diameter attached to a 27 inches long wooden handle. Sixteen forward and sixteen back.
34 COTTON JASSID IN THE PUNJAB
ward strokes with this hand-net in the middle of the plot were made at each time. It is obvious that only the adults were caught by this method.
This method has been criticized by DeLong (1932), as, according to him, samples of insects colJected by this method from different localities would vary with the prevailing conditions such as temperature, humidity, wind velocity and direction, the position of the sun and size and the condition of the crop. In the present studies, however, the insect population was determined at Lyallpur only and the following precautions were taken to increase the accuracy of the work as much as possible :-
(a) As far as weather conditions permitted, the sweepings were done in the morning hours only and the work finished in a reasonably short time;
(b) The direction of the sweeps was always against the wind; (c) Sweeping on adjacent plots, one after another, was avoided; and Cd) The operator and the appliances were the same thoughout. (ii) Counting.-Three to five average sized plants from each sub-plot 10
each repetition were selected at random and all the nymphs were counted on all the leaves.
(iii) Fumigation.- Here again th ree to five normal plants were selected in each bed of all the replications. Sheets of white paper were spread under each plant and a fumigation chamber was adroitly placed over it. The plant was then fumigated by Calcium cyanide. The adults and nymphs were, thus, killed and were later carefully counted both on the plant and the paper spread underneath it.
Standardisation of the methods of estimating population (i) Sweeping.-The size of the sub-plots in the American varietal tests was
about 1/173 acre each year. In determining the number of strokes of the hand-net care had to be taken that on the ooe hand the entire plot should be covered and, on the other, the plants (and therefore the population) in the contiguous plots should not be disturbed. Different numbers of trial strokes were employed and it was found that sixteen forward and sixteen backward strokes were the ideal number for an 1/173-acre plot size. This number was adhered to throughout the co urse of the present in vestigation.
(ii) Counting.-This is a very cumbersome and time consuming operation as all the leaves whose number may go up to 353 when the plant is full grown (Afzal, 1933) will have to be examined. It was, therefore, necessary to determine the size of the sample to reduce the work without in any way impairing the efficiency of the method. For this purpose two varieties, 199F and 'Victory' were selected. 199F usually has a very low population, while under the same conditions, 'Victory' is very highly attacked. Nymphs were counted cn twenty average-sized plants from the middle of the plot of each variety and the standard deviation and the coefficient of variability of the data were calculated and are given in Table XV (Ghani, 1945).
to.O ~ ._ .... I'::! ;:! 0 l.J
?
'" 0 ...::::
> .... ... X E iii ...
...:::: .....1 .., I'Q ...: ....
E-o ..0
'" .~
'" .a '" ~ .;; P., E ~
C/;)
POPULATION OF e. devastans ON COTTON PLANT IN PUNJAB 35
L ~ J. __ ~...!.~ ___________ -,;"", __ _
'" 01 <"'"l N "": tv; 0 T-i
I ...... N t-- II"}
~ 0 0
(" ... "j
.... U") '-0 T-i ...... q "<t-
<;~ -.---- .. ~
o: <"'"l ...t= _____ ~ _____ . ___ \O_ ~ ___ . ____ ._ .. __ . ___ _
U")
c-i
t"-<"'"l CIJ ci 0 0 ~ 0
"<t-.... l.tl <:'-1
'" ..;-Cf:/ T-i
0\ .... '""l
N q rrJ
1:-: 0 t--
'<t U")
N .... t-- 0\
Cf:/ ~ ~ 01 <"'"l _______ rrJ_,__ __ _ U") ~
---~--~---
N
0 0
'" l.tl tv; <:'! ,...., ..;-
CIJ rrJ 01
~ r-: '<t 01 ..;.
'" \C
t"- O <"'"l II"}
"1 CIJ (f") 0 ....
U") '" II; t--cq Cf:/ ~ ,...., N rrJ t--
t-- <"'"l 0 '<t .... ...... N '"
CIJ 01
N ..;- 0 .... ~ ci ..;. U")
t-- --_ .. _--------- _.---N CIJ 0 t-- CIJ U")
~ q ~ ~ "1 01 U") o
N ,...., rrJ 0 CIJ _~_,_._._._ ... _~ ______ ,_~ ___ t_-_ . __ ~ _____ _ ci ,....._--
CIJ .... (f")
.... N 0 rrJ "": 01 U") ,ri
...... t-- 0 ..;- \lJ q .... t-- N
N .---~---
, tl (1$
'-' 'k q ct!
> .S ..... ..... ct! 0 ..... :> II)
"0 a""' "0 .~ +1 .... C1l u'-'
"0 tE.c c: Cl,I._ ct! o~ .....
en U..o
t--01 ~
N rrJ N N t": ci t-- ,....,
-_ .. - .. --~-.-.
t .... \C>
"1 C'! 0\ \0
"<t-
...... , +1 .~ .._.. ... i:I
ct! ::-
c: .£ .9 .....
ct! ...... ..... .;;: 0 C1l
'5 Cl,I
"0 .,_, 0.
"0 0'-' 0 .~ tI 0. H
C1l u-c:: "0 tE.c ct! c:: III Cl,I .....
C1l 0:;:: ~ ....
if) U..a
36 COTTON JASSID IN THE PUNJAB
It will be seen from Table XV that in the case of 19')F a minimum of ten plants is essential while in 'Victory' counting of nymphs on five plants would give a reliable measure of the nymphal population. In our studies the number of plants was always above these lower limits and the conclusions arrived at should, therefore, be valid.
(iii) Fumigation.- This method appears to be the best of the three methods, as it takE's into account both the nymphs and the adults. In practice it was, however, found so difficult that it had to be given up after the first two years. During both these years only two plants were taken per plot.
Opinion has sometimes been expressed that although the number of nymphs per plant may be the same, yet the effect on one plant may be quite different to that on another, simply because the leaf-area and hence the feeding surface offered by the two plants is different. In order to test this point three varieties, J99F, L.S.S. and 'Victory' sown in randomized blocks were selected. Two average-sized plants from each bed were selected and their leaves were stripped systematically. The nymphal population on each leaf was recorded. The maximum number of leaves per plant in each variety is given below :-
199F
L.S.S.
'Victory'
171
189
257'
The population on a random sample of 10, 20, 30, 40, 50, 60, 80 and 100 leaves W:JS later calculated and the mean population, standard deviation and the coefficient of variability were worked out. These data are gi ven in Table XVI.
It will be seen from Table X VI that after a random variation in the coefflcient of variability up to 50 leaves in L.S.S. and 199F and 60 in 'Victory', there was a gradual fall but it did not become constant even up to the limit of 100 leaves. This would mean that the larger the number of leaves examined, the more accurate the data would be.
In order to find out the leaf area, alternate leaves of all plants were sketched on paper and their area was later measured by means of a planimeter. Thus the jassid population, per plant, per leaf and per 100 sq. ems. of leaf area was worked out. The data obtained were analysed statistically and the resllits of this analysis are given in Table XVII.
POPULATION OF e. devastans ON COTTON PLANT IN PUNJAB 37
I 00 ..... (,,1 tt") rf) ..... [-... ..-r 01 01 0 ..... 0 . ,.... 01 i,O 'i" ..... ..... O'i ..... ('1j ..0 \.0 \0, \0 01 + co .... i co ~ ..... t; 0 ~ ~ 0 1--
I 0 0 <0 0 0 01 H 0 t<'l .. ----~----.-.. -~~---------.-.---,---~.--------~-,-
10 [-... 00 0 [-... 00 CO 11') \.0 N N 00 ..-r '7" .-< N N 0'1 0
ICIJ CO r--- + .... H N 0 11') N t- ..... ex: 00 .-< t; c: ..... C;
I 0 0 N 0 0 ('1j ..... 0 II") , _________ <:'_l_
.-----.~~---~
..... -~.-~-~ - ... --.~-~-. 1------ -----_.,,----_ .. _, .
10 8 0'1 N 00 !Y.l i,O 0 0'1 i,O + ('1j .... + 00 ('1j II") ('1j
\0 II") 0. 00 r-. 0 {'-o + 00 N {'-o .... 0; [-... ...... 11; ~ ~ CO 0 0 I/") 0 0 ('1j rl 0 {'-o
__ ~_S'_l ____ ~ .. -.. --~.---- -,. -_":"""_---------- .....
<IJ (» ;;-
0 !Y.l ('I tt") ..,.. 1(") ..... 0'1 \0 ('1j c<l ..... ..... \0 O. OCJ !>I 0 N IN ~ 11
(") N N ,....; co {'-o ..... CO U; IN - OCJ N 0\ {'-o ~ ~ r; ..... 0\ 4-< I 0 ci -D 0 0 N rl 0 N 0
101 r:-l N ________ ,.,
.-~.-. I-< (»
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~ ('1j H ""
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38
Population
COTTON JASSID IN THE PUNJAB
TABLE XVII
Mean jassid population.
Varieties \ ------1
199F L.S.S. I 'Victory' I S.E.
Critical difference
at 5%
~-'--~----'- ---.-~ -----·-I-------~ -_---84.333 [I :.':: 2.977 ± 11.687
0.933 -+- 0.038 ± 0.149
Per plant 51.783 61.933
Per leaf 0.489 0.680
Per 100 sq. ems. I 1.151 l.520 of leaf area
3.407
The order of infestation was as under:-
Per plant 199F
Per leaf i99F Per 100 sq. ems. of leaf area 199F
± 0.166
L.S.S.
"C'S':'s. L.S.S.
± 0.651
'Victory'
'Victory'
'Victory'
It may, therefore, be concluded that as the order of infestation remained the same by all the three methods, the number of leaves examined on the plant or the leaf area did not make any difference. It would, however, be preferable to count the nymphs on the entire plant and this method was used throughout these studies.
Comparison of the three methods of estimating the jassid population
A peculiar difficulty in the statistical analysis of the insect population is that there are great possibilities of arriving at wrong conclusions because the calculated mean infestation is sometimes upset due to the swamping of results in a series of observations by very high numbers (Afzal, Nanda and Abbas, 1943). The study of insect population over a number of years invariably gives rise to scew distributions. The degree of infestation in such cases cannot be computed merely from the arithmetic means and the application of the statistical formulce also becomes invalid. It, therefore, becomes necessary to transform the data in such a way that the transformation would act like the square root transformation for low numbers and like lhe logarithmic transformation for large numbers. Williams (1937) in his studies on the number of insects caught in a light trap has used the transformation, y=Iog lO (n+l). This function approximates to Y =h/-;-for low numbers, and, at values of n above 10, it departs from square root curve and approaches Y = log n, from which it is practically indistin~
guishable at values of n above 100. This transformation prevents the swamping of
POPULATION OF e. devastans ON COTTON PLANT IN PUNJAB 39
results, makes the distribution normal, and affords a valid basis for estimating the insect population on different dates or different varieties.
When it is intended to compare t he degree of infestation of different stra~ns, from the insect population counted throughout the season by the method of analysis of variance, the same transformation must necessarily be used. It must, however, be admitted that, since the variance is proportionate to the square of the mean, a very highly susceptible variety included in the experiment would increase the error variance and the small differences between the varieties
would be masked.
Cochran (1938) has dealt with various difficulties encountered in the analysis of variance and has suggested transformations for different types of data so as to arrive at valid conclusions. These transformations are given in Table XVIII.
Distribution
Poisson
Binomial ~ I
TABLE XVIII Transformations suggested by Cochran
Data
Small whole number (x)
Fraction (p)
Percentage (P)
N umbers (x) ...
Relation betweenl variance and I
mean I
V=x V= p(l-p)
n V = J>_(!O_O.P)
N V=AX2
Transformation
----.~-.. -
.J-;-
Sin-lv'p
Sin-l.,1 _~_ 100
IOglo
I Variance in new scale
-----_._-_.-
I 1/4 821 n
821 n
I 0.189)\
In order to find out the best transformation for the jassid population, the mean and the variance of the figures were worked out and it was found that best results were obtained by the transformation log (n + 1).
To further test the validity of this transformation the analysis of variance of t~1e original as well as the transformed data, from a large number of varieties for a number of years, were worked out. The order of significance of both the actual and the transformed figures are given in Tables XIX and XX.
A comparison of these two Tables shows that the transformed figures give a much more precise measure of significance than the original data and the relative density of population is brought out much more clearly than from the original figures.
When a new strain of cotton is produced at a Cotton Breeding Station situated in a jassid-infested locality, the Cotton Breeder w01.dd like to know the
40
I'~ C\I
~
I~
C/)
u)
...i
In N
COTTON JASSID IN THE PUNJAB
ll"l C\I
C/)
C/)
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tl/)
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.. ~ .>
I~
.. ~--~--- ~------'-
!L. o o rI
POPULATION OF e. devastans ON COTTON PLANTS IN PUNJAB 41
iLl o o rl
u5 r.t:5
.. ,..;.1.
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r/)
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\1 .------.. - .. -- ...... ~--------
42 COTTON JASSlD IN THE PUNJAB
reaction of the new variety towards this pest. If, for this purpose, the odginaI data are used the danger of masking the slight differences in resistance or susceptibility become n:ore mar ked. It is, therefore, necessary to analyse the transformed figures.
Comparative incidence of the pest on different varieties
Although a very large number of varieties has been under experiment (Table XX), the varieties commonly grown in the Province as well as their regions of growth are given below. It may be mentioned that the Cotton Control Act was promulgated early in 1949 and the regions for different varieties have been clearly delimited.
4F. - This is the oldest commercial Punjab-American variety which was cultivated for the first time in 1914. This variety is grown in Jhang and parts of LyalJpur and Montgomery districts.
L.S.S.--This is a selection from 4F and was released for general cultivation in 1934, It is grown in Lyal1pur, Sheikhupura and Sargodha districts.
289F/43.- This variety was approved for distribution in 1934 and is grown in parts of Montgomery district.
Victory.-This variety was approved for general distribution in January, 1945, a.nd is grown in Multan, Muzaffargarh and Dera Ghazi Khan districts,
I99 F.-This is the latest and the best variety of American cotton grown in the Punjab. Its cultivation is, however, confined to parts of Multan district.
Considering these varieties only in Table XX, it will be seen that 4P, L.S.S., 289F/43 and 199F show the minimum jassid incidence while 'Victory' is severely infested. It may, however, be mentioned that the region of growth of 'Victory' is hotter and drier than the rest of the Province and jassids are not likely to be a
serious menace there.
Comparative incidence of the pest in different regions of the Province The attack of E, devaslans is not uniform in all the cotton fields in a parti
cular locality. One :field may be heavily infested and a contiguous field may practically escape the attack. Previous workers have also made a similar obser~ vation. Haines (1925) says that, in South Africa, the severity of the attack of E. facialis is dependent upon soil drainage and other agricultural conditions. Vuillet (1924) working in the French Sudan came to the conclus:on that the damage done to the cotton plant by E. facial is was much less in fields rich in mineral fertilizers, especially Potash. Parnell (1925-26) found, in South Africa, that drought Of water-logging predisposed the cotton planr to jassid attack. Mumford and Hey (1930) have pointed out that a disturbance in the water content of the plant rendered it more susceptible to the attack of sap-feeding insects.
POPULATIOr:r OF e. devastans ON COTTON PLANT IN PUNJAB 43
During the course of the present investigation it has been seen that although the attack may varyJrom field to field, yet, if several varieties an~ sown together, as in randomized varietal test plots, the order of comparative severity of attack on any particular variety remains practically the same from year to year and from place to place. Figures on this point are presented in Table XXI.
It will be seen from Table XXI that a large number of varieties was under ohervation, for three years in widely separated localities in the Punjab. The
jassid attack was also of a very different intensity during these years; 1942 being
the year of heaviest attack and 1940 of the lowest. The order of incidence of attack, however, did not show any great variation. A variety with a low population in one place in one year had a low incidence of attack in other places and in other years. A variety showing a high attack in one place also showed a high attack in other pJaces in all the years. It would, therefore, be safe, from the economic point of view, to select and grow those varieties which show a low incidence of jassid population, because the variations in soil and agricultural condi tions do not make much difference.
Seasonal and annual variation in the population of E. d~vastans on cotton
The inci dence of jassid attack on cotton was estimated on the different varieties grown in the varietal test plots on every tenth day throughout the course of this investigation and, [or the sake of illustrating the seasonal and annual variation in the population, the number of jassids present on two varieties, namely, L.S.S. and 289FIK.25 (a resistant and a susceptible variety) is shown in Table XXII. As the figures given in this Table are the totals of the counts from all the replications, these must be considered as very reliable.
It will be seen from Table XXII that the jassid attack starts at Lyallpur about a month and a half after sowing, i.e., from the middle of
July and rises rapidly to its peak in the middle of August. It then declines steadily until it practically disappears in the beginning of Novernbu.
It is also seen that the attack was usually higher in 289FIK.25 than in L.S S.
It was also seen that besides the seasonal fluctuations, there w£re annual fluctuations, some years like 1939, 1941, and 19~2 being years of very heavy infestation. The causes of these outbreaks are not yet fully understood, but it may be generally stated (Afzal, 1941) that severe infestltion occurs in years of heavy rainfall with the consequent high atmospheric humidity.
The occurrence of annual and seasonal fluctuations has been noticed by other workers. Peat (1928) working in Rhodesia observed that the incidence of the pest increased in the end of March after rains and fell down with the senility of the plants in May. Parnell (1934) noticed in South Africa that the jassid attack was very high after the rains. Sloan (1938) came to the conclusion that in
,,; . ~ :~
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COTTON JASSID IN THE PUNJAB
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POPULATION OF e. devastans ON COTTON PLANT IN PUNJAB
u5 rfJ
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45
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46 COTTON JASSID IN THE PUNJAB
Queensland severe attack of jassid was associated with cloudy weather and the undue sappy growth of American varieties. Prentice (1939-40) has stated that in Tanganyika March rains herald the real attack of jassids. Peat (1942-43) has observed that jassids are unimportant in districts of Tanganyika where rainfall is low and that jassid damage seemed to be linked with wet years.
It will be seen that the effect of climatic conditions, particularly that of rainfall on the incidence of jassid attack, has been noticed by many workers but no attempt seems to have been made to study the correlation of these two factors. It was, therefore. decided to find out if there existed any correlation between meteorological factors, such as temperature, humidity and rainfall and the intensity of jassid attack (Afzal and Ghani, 1949).
The records of jassid population on different varieties of cotton are available for 9 years. The average jassid infestation throughout the season was calculated by transforming the data to log (n+1) for one variety (289F/43), which was under trial for all these years. The figures so obtained have teen designated as "Jassid Index". The average mean temperature, humidity and total rainfall were taken for jassid season i.e., from June 1 to November 1. These data are given in Table XXIII.
The weakness in taking the average figures of temperature and humidity is realized, as it is within the limit of possibility that an unusually hot day occurring anywhere in the season may kill a very large number of jassids. Such an occurrence, however, is not a common phenomenon during the period of severe attack of the pest. The population usually increases in the normal geometric ratio. Again the meteorological records are from the Stevenson's Screen fixed outside the cotton
TABLE XXIII
" ] assid Index" and climatic conditions
Year I J assid Index Av. mean Total rainfall Av. relative I temperature humidity I
"'" .. ----~-~~----- --1937 1.6114 88.9 5.7 53.2 1938 1.0266 88.0 5.8 55.2 1939 1.3086 89.2 5.6 54.8
1940 1.6103 88.6 3.4 58.6 1941 2.1088 88.3 12.11 638 1942 1.9797 86.9 12.04 65.6
1943 1.9837 88.1 9.87 63.2 1944 2.2134 86.3 10.80 70.2 1945 2.3741 87.5 10.87 68.7
r ,3.0
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~ 7·0 l-I-
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( 65
:t c:: 60 ! p
L 55
r Z·o
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corras ]ASSIO IN THe. PUNJAB
T£ MPE RAT()R£
. . .
:'t ., .. , .• '. . . . . '.
••• ' ••• I~···'· 0.,
......... RAI/tII'AH
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\ \ \ \
36
'. ~'i
",-"of. HUMIDITY
JA551D l!Vb!){
43
. 12
----- OBSERvED
CALCULATED
Fig. 2.-"Jassid Index" and climatic conditions.
POPULATION OF e. devastans ON COTTON PLANT IN PUNJAB 47
fields and, therefore, do not depict the microclimate in which the nymphs live. The present attempt may be considered only as a preliminary one for finding out the association of a pest with climatic factors.
It is quite evident from Table XXIII that there was no apparent association between" J assid Index" and the average mean temperature. This fa ctor was, therefore, not considered further.
The simple correlations between "Jassid Index" and relative humidity and rainfall were worked out and are given below :-
" J assid Index" and relative humidity
r= + 0.813978 Highly significant ,. ]assid Index" and rainfall
r= + 0.685762 Highly significant
Both these correlations were positive and statistically significant at 1% level. This shows that "Jassid Index" increased with the increase in humidity or rainfall.
The multiple correlation between" Jassid Index," relative humidity and rainfall was found to be r= 0.8145, which is again statistically significant at 1% level. In order, however. to work out the real association between "Jassid Index," relative humidity and rainfall, partial regression equation was fitted to
the data. The equation is given below :-J. I. = 1.172005 +0.048185H + 0.005995R
where J. I. =" Jassid Index" ; H. = Average relative humidity; and R. = Total rainfall for the jassid period.
It may also be added that the partial correlation coefficients of these three factors were individually non-significant. This shows that rainfall or average relative humidity alone had no effect. As the multiple correlation was significant it may be deduced that both these factors acting together affected the "J assid Index ".
The values of" Jassid Index" were calculated from the partial regression equation and the calculated values along with the original data are depicted in Fig. 2. .
It must, however, be emphasized that this is only a preliminary attempt to correlate the biological phenomenon of variation in jassid population with meteorological factors and the general statement made earlier that a high jassid attack is co-existent with high rainfall and high relative humidity can be only roughly verified.
48
CHAPTER IX
AGE OF LEAF AND JASSID POPULATION
The age of leaf which is preferred by the female for egg-lay jng is important, because the young nymphs do not move about very much and the feeding of the nymphs and the subsequent injury to the plant takes place near the site where
eggs are laid. So far as we are aware, no work on this problem seems to have been done anywhere up to this time.
DeLong (1928) found, in the United States of America, that E. fabce does
not select potato plants for food or oviposition till the plants have attained can· siderable growth. Smith and PODS (l931) have carried out extensive experiments on six species of jassids and as a result of this work have divided these species into two groups, viz., those which feed exclusively on the mesophyll tissue and those in which feeding is confined to the phlrem tissue. In the former case the insect prefers mature foliage while in the latter immature and succulent leaves are preferred. It has also been reported from Queensland that E. maculata attacks the succulent terminal leaves of the cotton plant in preference to older leaves CA. W. S. May, private communication), The age of 1eaf preferred for feeding and breeding is of considerable importance as the so-called "jassid effect" (MacDonidd et ai, 1942·43) or the "symptom picture" (Wells, 194-3) can be best judged from the zone of the plant which is liable to the worst attack. There is also another aspect of this problem. In any sampling studies where the leaf area is to be
correlated with the number of jassids, it is of importance to take those leaves on which the oviposition is highest and, in any comparative study, leaves from the same plant zone should be taken.
The feeding habits of E. devastans appear to be entirely different in the Punjab. They do not cause "stippling" nor does the entire leaf ever. wilt. There is. on the contrary. a pronounced crumpling of leaves followed by the drying up of leaf margins. The crumpled area becomes brick-red and dries up.
In order to find out the association, if any, between leaf age and oviposition, two varieties, 199F which is very resistant and 289FIK. 25, which is very susceptible to the attack, were chosen. Pure seed of these two varieties was sown at the optimum time (17-5-43) and five normal plants were selected early in the season. All the leaves on the main stem of these plants were tagged and numbered on the date of separation from the terminal bud. The age of all primary leaves was thus known.
Oviposition could not be studied by the usual method of dissection of the leaf-vein as this necessitated the plucking of the leaves. It was, therefore,
CCOTTON JASSID IN THE: PUNJAB
\·4 199F 1·3 I·Z /"'\
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0.0 /0 15 20 2$ 30 3S '10 4$ 5~ 5S 60 65
A6E OF lEAF lili bAys
- - - - - OBSER,VED
( 4LCUL AT! () 2.3 289 F /1( 2S 2.2 ;..,
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A6l OF LEAF IN DAYS fig. 3.- \ e of leaf and nymphal population.
AGE OF LEAF AND JASSID POPULATION 49
decided to study oviposition indirectly by counting the number of nymphs on each leaf on alternate days. After counting, the nyrpphs were killed and removed from the leaves. In this way the number of nymphs (and hence indirectly the number of eggs laid, as hatching percentage is practkally equal and very high on all varieties, cf. Verma and Afzal, 1940) on leaves of different ages was calculated. The experiment was confined to the primary leaves but there is no reason to believe that other leaves would behave differently from the primary leaves in this respect. The data for egg-laying are shown in Fig. 3.
A study of Fig. 3 shows that the number of eggs increased with the age of leaves in both the varieties, the maximum number being laid on leaves between 35 to 45 days old in 199F and 30 to 40 days in 289F/K.25. It will also be observed that the peak was much higher in the case of the susceptible variety as compared to the resistant one.
In order to interpret the results statistically, polynomial curves were fitted to the data. with nymphal population as the dependent and age as the independent variate. The sums of squares attributed to the linear, quadratic and cubic regressions as well as the residuals,are given in Table XXIV.
Variance due to
Linear regression
Quadratic regression
Cubic regression
Residual
Total
TABLE XXIV
Sums of squares and mean squares.
199F I 289FjK.25 Degrees
of -~- -~. ---_._-_-, -------- ____ .r""_
I I freedom Sums of Mean Sums of Mean
squares squares
I squares squares
~-------
I 1 0.103994 0.103994 0.138509 I
0.138509
1 3.412654 3.412654* 15.256977 I I
15.256977* I
1 0.076496 0.076496 I 0.238211 i Q.23821lt ! !
I \ 48 1.472807 I 0.030633 I 2.077108 i 0.043273 ---------,(--1----51 5.066951 I ... 17.710805 I ...
I ' • Significant up to 1 per cent level. ,(Significant up to 5 per cent level.
It will be seen that in both the varieties the quadratic trend was highly significant, though in the susceptible variety even the cubic regression was also significant. From this it can be inferred that the insect prefers mature leaves to
50 C0T10~ JASSID IN lHE :PUNJAB
the young and the very old ones for egg-laying. It may be mentioned here that the cotton leaf is full-grown at the age of 22 days (Afzal, 1933).
The second-degree parabolas fitted to the curves are given below and are ~hown graphically in Fig. 3.
where
199F y= -0.839609+0.092420 x-0.001272x2 2R9F/K.25 y = -1.741029+0.192936 x-0.002690x~
y=nyrnphal population, and x=age of leaves in days.
The difference in the span of the two cUlives can be oSserved by the ratio of latera recta, which is 2.120, showing a highly peaked nature of the curve in
289F/K.25 and a flat peaked nature in the case of 199F.
The rate of increase in nymphal population can be determined by dy/dx and the rate of this increase by dIy/ dx3,
These values are given below ;~ dy d!y dx dx3
199F + 0.092420 - 0.002544 x - 0.002544 289F/K,25 -t- 0.192935 - 0.005380 x - 0.005380
The values of dy dx and dZy/dxll. once again indicate the p~aked nature of the curve in 289F,K.Z5 and a flat one for 199F. The coordinates of vertices of the curves are 0.839 and 36.33 for 199F and 1.719 and 35.86 for 289F /K.25. These values show that the maximum nymphal population was observed on leaves of about the same age (35 days) in both the varieties and that the maximum population on 289F/K.25 was more than double that on 199F.
This experiment was repeated in 19+4 with the same varieties sown at about the same time. The method of numbering of leaves and counting of nymphs was also the same. In addition to the nymphal popUlation, the hairiness and the toughness of the leaf-veins was also recorded to see the effect of these two factors on oviposition. The methods of measuring the toughness and counting the hairs have been described elsewhere. The data collected for the two varieties are given in Fig. 4.
It will be seen from Fig. 4 that there were no nymphs on the leaves till they reached the age of nine to ten days. The population then steadily increased till it reached the maximum at the age of 39 to 45 days in 199F and 46 to 54 days in 289F/K.25 after which it steadily decreased and disappeared altogeth~r at the age
of 69 days in 199F and 73 days in 289FjK.25. The equations fitted to the second,< degree parabolas shown in Fig. 4 were worked and are given below :-
199F y=1.9639tO.O}0799x - 0.001863x2
289F!K.25 y=3.0759 to,0225x - O.002008x2
II' IS
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4S'f)
-400 "j$tI
JOO q .15"11 ~ 2.""~ d·o~ 100 So
l}5'o", !jlCI~ I 5"(1 ~ I ,,., ~
5. ~ o
Fig. 4.-Age of leaf, nymphal population, toughness and hairiness of leaf-vein.
AGE OF LEAF AND ]ASSID POPULATION .51
By taking the differential of the above equativns it is found that the population is theoretically at its maximum at the age of 43 days in 199F and 49 days in 289F/K.25.
It is also seen from Fig. 4 that the peak, is practically double that on 199F. the findings of 1943.
population in 289F/K.25, when at its All these results substantially confirm
The association between the: nymphal population and toughness and hairiness of the leaf-vein was then investigated. In order to assess the effects of these two leaf-characters separately on the oviposition, partial regressions were worked out for the two varieties. These are given below :-
199F Partial regression of oviposition on toughness = + 0.007805 (Non-significant) Partial regression of oviposition on hairiness
289F/K.25 Partial regression of oviposition on toughness Partial regression of oviposition on hairir.ess
= - 0.001755 (Si!l.nificant)
= - 0.009436 (Non-significant)
= - 0.0111109 (Significant)
It will be seen that the partial regressions of oviposition on toughness were non· significant in both the varieties, while those of oviposition on hairiness were significant in both cases. It need not, however, be deduced that toughness does not play any part. The above regressions have been calculated from the entire data:' and it is within the limits of possibility that the extreme tenderness of veins, when the leafis very young, masks the effect of toughness on oviposition. Similarly, in the case of hairiness the smaller number of hairs when the leaf becomes old (cotton leaf hairs are known to be deciduous) contributes to the decrease of the regression, though not to the extent as to render it non-significant. Although more experiments are necessary to establish the exact relationship of these two characters with oviposition, yet it may be stated that both of them play their part; hairiness plays the predominant part in preventing oviposition when the leaf is young and toughness plays the same part when the leaf is old. In the middle of this period, i.e., at about the age of 40 -50 days, the inhibiting effects of these two characters are of a very moderate intensity and oviposition is at its highest. At this age the hairiness has decreased sufficiently as not to impede egg· laying and the veins have not attained sufficient toughness to seriously interfere with the penetration of the ovipositor.
52 COTTON JASSID IN THE PUNJAB
CHAPTER X
EFFECT OF AGRONOMIC FACTORS ON JASSID POPULATION
Observations on the effects of agronomic factors on the incidence of jassid attack are fairly numerous but the results of detailed experiments have been rarely reported. Lees (1926) has made a distinction between 'resistance' and 'endurance.' According to him 'resistance' can only be brought about by breeding but' endurance " or 'acquired resistance' can be modified by changing the condition of the plant by various agronomic factors, such as irrigation, time of sowing, spacings, fertilizers. etc. Ballard (1927) found that, in New Guinea, the crop raised on red soils with low Potash and Phosphoric acid content suffered more than the crop sown on other types of soil. Parnell (1927) in SQulh Africa and Peat (1927) in So~th Rhodesia, found that fertilizers were ineffective in changing the incidence of jassid attack. Golding (1928) noticed that, in Nigeria, jassids were abundant on cotton planted on poor soils. Hargreaves (1934), working in Uganda, has stated that prevalence of jassids was correlated with the poverty of soil and inadequacy of water supply during dry weather. McKinstry and Prentice (1936) observed, in Southern Rhodesia, that an early sown crop suffered from the attack of jassids for a longer period. Sloan (1938) found that, in Queensland, the cotton crop on rich alluvial soils was heavily infested with jassids and that late sown crop was particularly susceptible. Stenhouse (1939) reported from Fiji that cotton jassid, though usually present, wa3 menace only to the late sown crop, while the early sown crop did not suffer at all. Jameson (1939) found that, in Uganda, the May and June sown crop had very low jassid population, while the July and August so wings suffered seriously. Prentice (1940) found that, in Tanganyika, the late sown cotton crop suffered more than the crops sown early. Peat (1943) observed that the attack of jasdids on poor soils in certain areas of Tanganyika was very heavy indeed. Afzal Husain and Lal (1940) have stated that, in the Punjab, late sown crops suffered more from the attack of jassids but Dastur (1944) found that, although the normally spaced late sown crop suffered heavily, the closely spaced late sown fields showed less att ack.
In order to assess the effect of some of the most important agronomic factors detailed experiments were carried out and the results are presented hereunder (Afzal and Ghani, 1949b). It may be mentioned that the jassid population was determined throughout the season at an interval of 10 days by counting the nymphs and sweeping the adults with a hand-net. The data obtained in all these cases were subjected to statistical analysis by transforming the same to log (n + 1).
EFFECT OF AGRONOMIC FACTORS ON JASSID POPULATION 53
Eff,,:t of date of sowing on jassid population
The first experiment of this series was carried out on two resistant varieties,
L.S.S. and 289F /43 and the jassid population in each sowing was recorded by the method of sweeping. The spacing employed was 3 feet between the rows and 15" to 18" between the plants. It may be mentioned that this is the normal spacing recommended by the Department of Agriculture for the Punjab-American varieties. There were 5 replications laid out in randomized blocks. The population was determined thrice a month from all the beds and the total number of jassids per month from all the plots of each date of sowing are given in Table XXV.
TABLE XXV
] assid I!0pulatiort on two varieties sown on different dates.
Variety and date of sowing
------------------:--.--------~--~ ....... ~ ... --.... ---
Months L.S.S. 289Fj43
-~--~.-~-------.--- -- ----~-~-~~ ----...,.-------0--- -.. --........ -~ ...... --5/5 I 20/5 I 4/6 I 20/6 5/5 -----:--- ---I---I---·~-- ..
~:~: :: 4~ '''431 '''35 Ii "'52
August.. 319 272 I 418 590
32
202
20/5
1
45
345
229 158 September 151
October... 20
428 1941 172
49 I 28 30 22 41
Total ... --5331
--4-95-i --7-23-1-- l1i91- 456 --;);-
4/6 I
42
652
369
34
1097 [
20/6
29
511
320
55
915
Tho: different dates of sowing employed in this experiment fell within the optimum period recommended for sowing American cotton at Lyallpur (Trought, 1930). It is seen from Table XXV that the jassid infection started simultaneously in all the sowings in July but the attack incr~ased more rapidly and reached a higher peak in the later sowings than in the early ones.
Effect of spacing on jassid population
The effect of spacing on jassid population was also investigated, in the first instance, on L.S.S. and 289F /43 as these were the two most important commercial
54 COTTON JASSID IN THE PUNJAB
varieties of the Province. The layout of the experiment was as shown below: -
Varieties L.S.S. and 289F/43 Spacing between the rows ...
Replications
2~ ft., 3 ft. and 3~ {t.
6
Jassid population was determined by counting and sweeping and total population in all the replications is given in Table XXVI.
Method
Counting ...
Sweeping ...
TABLE XXVI
Jassid population in different spacing3.
Month
July
August
September
October
Total
July
August
September
October
Total ...
I 289F/43 1--
____ I L.S.S.
2t' 3'
-.-.-- -------
21
78
36
77
941 l1042
89 86
30
79
31
52
29
68
822 1085 781
132 203 226
18
86
916
218
1129 _1241 1063 _13~ll104 1238
417 313
59 75 ';'3 59 63 59
1051 1092 1041 11886 1595 1788
305 279 390 585 578 449
1419 11447 1511 2533 2237 2299
The statistical analysis of the figures showed that the differences in j assid
population in different spacings were insignificant. It must, however, be mentioned 1 hat the range of spacing used was very narrow and the results have, therefore, failed to bring out clearly the effect of spacing on jassid population. Amongst the varieties there was no difference by the method of counting, but, by sweeping, L.S.S. showed significantly higher population than 289F/43.
The experiment was repeated by using a susceptible variety (289F/K.25)
EFFECT OF AGRONOMIC fACTORS ON JASSID POPULATION 55
with a much wider range of spacings (2', 3', 4' and 5' between the rows). There were six replications and the population was once again estimated thrice a month. These figures are gi ven in Table XXVII.
TABLE XXVII
Jassid population estimated by sweeping.
Spacings
Month ~--~--- ~---" ..
2' 3' 4' 5'
----~-- -.-.---
July 66 50 65 65
August 715 639 600 528
September 5221 5480 4887 5236
October 2729 2974 2367 2581
November 523 479 544 547
-~~--- ~----- ----~-- -----
Total 9254- 9622 8463 8957
The results were non-significant and it may apparently be concluded that even such a big range of spacing between the rows failed to affect the jassid population. As will. however, be shown later, the method of sweeping should not have been used in this exp::riment. The figures given in Table XXVII are, therefore, not a true indication of the popUlation per plant.
Effect of spacing~cum-sowiDg date on jassid population
It is now realised that plant life is conditioned by several interacting agronomic factors but these factors should not be considered individually as there is always a possibility of coming to wrong conclusions. A special case in point is the interaction of sowing dates and spacing. Both these factors were, as shown above, studied separately at first, but it must be conceded that the interaction of these two factors cannot be found out in simple layouts. It is known that as the sowing date is delayed the plants do not put forth as much vegetative growth as the early sown plants. For the proper utilisation of soil, therefore, the late sown plants must be spaced closely and these two factors must necessarily be considered together (Afzal, 1949). Simple experiments, either on date of sowing or spacing cannot give all the information that an agronomist would require and it is obvious that the effect of spacing and date of
56 COTTON J ASSID IN THE PUNJ AB
sowing on jassid population would be most satisfactorily found out from
complex experiments. Such experiments were carried out during two years, 1943 and 1944 and results of both these are discussed below :-
Varieties Dates of sewing
LAYOUT
4F and' Victory' 14/5, 4/6 and 2';/6
Spacings (between plants X between rows) l'Xl', l'x2', l'X3', 2'x2' and 2' x3'
Replications Layout
3 Fisher's randomized blocks.
The jassid population was determined, as usual, thrice a month throughout the season by counting and sweeping. Counting of nymphs was done on three plants per bed (i.e., 9 plants per treatment) and the adults were collected by 16 forward and 16 backward strokes of the h.:md-net, making a total of 96 sweeps per treatment.
The results were statistically analysed and the final figures of the analysis of
variance will be discussed.
(i) Varieties
The jassid population on the two varieties was significantly different and the mean values by both the methods are given in Table XXVIII:
TABLE XXVIII
Mean values of jassid population on varieties.
I Varieties I Method Scale IS. E. ± I Year
-----------1-___________ I--4F l'~ictor;' ___ _
Counting
Sweeping
... 1943 \ Log (n+1) 1.2207 1.5105 Antilogs 15.63 31.40
0.0093 0.0264
1944 Log (n+1) 1.7045 1.9429 0.0212 0.0602
". 1943
1944
Antilogs 49.64 86.68
Log (n+1) Antilogs
Log (n+1) Antilogs
1.0734 1.3181 0.0090 0.0254 10.84 10.80
1.4061 1.5579 0.0064 0.0180 24.48 35.13
It will be seen from Table XXVIII that 4F had definitely lower population in both the years and by both the methods than 'Victory'.
EFFECT OF AGRONOMIC FACTORS ON JASSlD POPULATION 57
(ii) Date of sowing The jassid population on the different dates of sowing was worked out and
is given in Table XXIX. TABLE XXIX
Mean values of jassid population on sowing dates .
. Method
Counting
Sweeping 1943
1944
Non-significant
Non-significant
Order of infestation by counting :-
1943 I Sowing -nrSOWlng' -liSowing--_. __
1944 I Sowing II Sowing III Sowing It will be seen from Table XXIX that the method of sweeping gave non
significant results, while the dates of sowing showed different population by counting, the first sowing had the least population in both the years as compared to the second and third sowing. There was, however, no significant difference between the last two sowings.
(iii) Spacings The jassid population in different spacings is brought out in Table XXX.
Method Scale
----'-- -- ---"_
Counting 1943 Log (n+l) Antilogs
1944 Log (11+1) Antilogs
Sweeping 1943 Log (n+ 1) Antilogs
1944 Log (11+1) Antilogs
TABLE XXX Mean values of jassid population.
Spacings 1_ g +1 ---.---------,------.---- S E ± <II.,
I ' "'~ k*
l'x3' , 2'x2' I 2'X3' i :c~u; l' Xl' l' x 2' iu:.o~ -"_- ---- --.. -, ' -""-1 . ---,,-
! I I 1.1846 14.30 1.5826
37.24
1.1705 13.81 1.5122
31.53
1.3561 21.71
1.8468 69.28
1.2127 15.32
1
1.4905 2\).94
1.4052 24.42 1.8659
72.63
1.1993 14.83
1.4920 30.05
,1.4304 1.4518 00147 'I' 0.0418 '125.95 27.30 '
1.8875 1.9355 0.0335 I 0.0591 76.18 85.20 I
[ I 1.2042 1.1919 Non-significant
15.01 14 .55 I 1.4668 I 1.4487 0 0100 0 0285
28.28 \ 27.09
58 COTTON ]ASSlD IN THE PUNJAB
Ord r of infestation :-
Counting 1943 1"xl' i' X 3' Z'xZ'
1944 I' xZ' l' X 3' 2' X 2' 2' X 3'
Sweeping 1944 2'x3' 2'x2i I'xZ' I'x3' I'xl'
It will be clear from Table XXX that the two methods of estimating the population gave different re'>ults. The jassid population was seen to increase
consistently in both the years from l' x l' to 2' x 3' by counting, while by sweeping practically reverse was found to be the case in 1944. In 1943 the results were non-significant by this method. The reason for this disparity appears to lie in the fact that in one sweep over closely spaced plants, the adults from a large number of plants are collected, while in the case of widely spaced plants, fewer
plants are swept over. The population as estimated by sweeping in this case is, therefore, not a true indication of the population per plant. It is, therefore, pointed out that, while sweeping is an easy and cheap method for estimating the jassid population in varietal test plots where all varietieo; are spaced uniformly, in agronomic experiments, where spacing is variable, the jassid population must be estimated by counting.
(iv) Interaction between varieties and spacings
The effect on jassid population on different varieties as influenced by spacing is shown in Table XXXI.
Method
I Counting 1943;
,19H: I \ i ,
sweepin g\ EH3:
i i
:194+1
Var:ety
4F
'Victory'
+1"
'Vict::>r)"
4F
'Victory'
'Victory'
TABLE XXXI
Mean jassid population (Log 11 + I).
Spacings ~---------- -~I-- ~---~~---- - S.E. + I'xl' I I' X::!' l'x3' 2'x2' I 2'')<3' -
I I
1.U036 11.2056 1.2552 1.3087 1-~-.~~~04- - I 0.0208
I I I
0.0590
1.3656 1..5056 1.5552 1.5521 : 1.5733
1.4342
1.7811
1.U311
1.3099
1.4367
1.5878
1.7283
1.9654
1.0764
1.3490
11.4028
11.5783
1.7505
i 1.9813
1.0731
1.3259
1.4086
1.5755
1. 7684
2.0U66
1.1059
1.3025
1.4106
1,5227
1 1.8+10
! 20300 1
, 1.01:;04 i
i 1.3035 I
1
1. 3721
1.5253
Non-significant
IN' 'fi ' on-slgnl cant
Non-significant
EFFEcr OF AGRONOMIC FACTORS ON JASSID POPULATION 59
This interaction was significant only in the case of counting in 1943, while in the rest of the three cases it was non-significant. As has already been pointed out that only counting can be relied upon wherever the plants are spaced differently and for this reason, the figures of population obtained by counting
will only be considered. Although the results of only one year are significant there is a tendency towards higher population with wider spacings on both the varieties.
(v) Interaction between varieties and sowing dates
The interaction is shown in Table XXXII.
TABLE XXXII
Mean jassid population (Log n+ 1).
bates of sowing 1
M th d e a y ear V . t ane y -----jSE .± 14/5 4(6 25/6 I
,-.---~. ····--1--1---· - -- --- _ .. .. -
Counting 1943 4F 1.1174 1.2508 1.2939 0.0161
'Victory' 11.3984 1.6452 1.4881
1944 4F 1.5534 1.6663 1.8937 \ 0.0367
'Victory' 1.8820 1.9425 2.0041
Critical d'ff I erence at 5% :±:
0.0458
I 0.10+2
Sweeping )1943 ' 4F 0.9669 1.1099 1.1433 Non-significant
'Victory' 1.2243 1.4191 1.3110
1944 4F 1.3750 1.3982 1.4453 0.0110 I 0.0312 I
'Victory' 1.5634 1.5773 1.5530 I
I I This interaction was significant in all cases except for sweeping in 1943
and. therefore, it is now possible to state that the late sown plants of both the varieties will be more severely infested than the early sown plants. 'Victory' will, of course, show a higher population of jassids than 4F in all the sowings. From the point of view of jassid infestation all cotton varieties in the Punjab must be sown early in May, as the later sown crop will be heavily infested.
(vi) Interaction between sowing dates and spacings
The interaction of sowing dates on spacings is shown in Table XXXIII.
60
Date of sowmg Method
I I Year
-------.- -------
H/5
+/6
Counting 11943
25,'6
19-1-1- H/5
+/6
25/6
Sweeping 1943 1+/5
4/6
25/6
1944 14/5
+/6
25/6
COTTON J ASSID IN THE. PUNJAB
TABLE XXXIII
Mean jassid population (Log n + 1).
Spacings -----~~--.------ ------ --- ""--
I
I'XI' I'XZ' 1')( 3' 2'x2' ---_._.
1 0265 12056 1.2932 1.3705
1.2066 1.4569 1.5136 1.5170
1.3207 1.4048 1.4088 1.4037
1 {+29 1.7260 1.7518 1.7979
1 -1417 18512 1.8812 1.8875
18632 19633 1.9646 1.9773
1.0506 1.1190 1.0S70 1.12J.~
1·2401 1 2750 1.2597 ) 1.2777
1.2207 1.2441 1.2519 1.2116
1.4811 1,4743 1.4830 1A626
1.5039 1.5029 1.+940 I 1.4800
1.5516 149+3 1.4991 I
1.457+
I
S.E.
2' x3'
... '" OJ U
~~
.cr t::+1 ..... OJ 'i:~~O
____ 1. ____ U~;_
1.3926 0.0255 0.0725
1.5459
1.+171
1.8698 Non-significant
1.9605
1.9762
1.0982 Non-significant
1.2700
1.2076 I 1.4-148
1.+579
I Non-.ignifi"nt
1.4434 I
The interaction between dates of sowing and spacing was significant only in the case of counting during 1943 and was non-significant for counting in 1944 and for both years in the case of sweeping. The figures given in Table XXXIII, however, show a tendency towards an increase in population in later sowings and wider spacings by the method of counting. The method of sweeping is, as has already been stated, unreliable wherever spacing is concerned and the figures given in Table XXXIII once again prove the same thing.
(vii) Interaction of the second order
The second order interactions between varieties, dates of sowing and spacings were non-significant in both the years by both the methods and, therefore, need not be discussed further.
(viii) The plant unit versus area unit for estimating jassid population
It may be stated here that the present authors were perhaps the first in the Pakistan-Bharat sub-continent to use modern statistical technique in the interpretation of the results of Entomological problems. This aspect was later emphasized by Pradhan and Krishna lyer (1945). Discussing insect populations, Pruthi and Pradhan (1945) have recommended that the population of insects
EFFECT OF AGRONOMIC FACTORS ON JASSID POPULATION 61
should be measured against a fixed scale on the basis of unit area of land. 'J.7e have, during the course of our studies, mainly determined the jassid population on the basis of number of plants. In some of our major experiments the combined effect of varieties, sowing dates and spacings on the incidence of j assid attack was determined. As the spacing was variable the number of plants could not have been uniform in all the treatments. and hence the scale on the basis of unit area of land would become invalid. This would be clear from the figures given in Table XXXIV.
TABLE XXXIV
Number of plants and jassid population on different spacings.
Jassid nymphs Spacing No. of plants
per plant ---------------- --------------1---------
I' X I' I' x2' l'~ 3' 2' x 2' 2'x3
43560 21780 14520 10890
7260
12.4 23.1 24.2 25.4 28.4
per acre
540579 502900 351529 276497 206184
It will be seen from Table XXXIV that the number of plants in various spacings was markedly different. The average jassid population was lowest (12.4) in I' x I' and highest (28.4) in 2' x3'. If these figures are converted to acre basis, jassid po_f>ulation becomes quite the reverse, being highest (340579) in l' X l' and lowest (206184) in 2' X 3'. It· may, therefore, be stated that in experiments where spacings are concerned or the stand of the crop is not uniform, plant basis for determining the population should be preferred. It may also be mentioned that in the present experiments, the jassid population has been determined against number of plants which is a fixed and uniform unit for that particular spacing. As the damage to the individual cotton plant depends upon the number of jassids present on it, only the plant basis of determining the jassid population can give a true indication of it and should, therefore, be adhered to. However, the size of the plants and the number of leaves in different spacings will not be uniform; the leaf area basis of determining the jassid population, probably, will be more accurate. But as this method is very laborious, time-consuming and necessitates the plucking of leaves, it may not be very desirable.
The yield of seed-cotton from the complex experiment
As the cultivator is mainly concerned with the produce which he gets from his crop, the yield of both the complex experiments was recorded. The -effect of differential jassid attack was superimposed on the effect of agronomic treat-
62 COTTON JASSID IN 'IHE PUNJAB
ments. Although in the present state of our knowledge it is impossible to assess the effect of these two factors separately, yet an attempt will be made to show the two together and to find out which of the two factors was more potent in affecting the yield. The jassid population has been dealt with in detail above and the Yleld will be discussed now.
(i) Varieties
The yield of the two varieties is given in Table XXXV.
TABLE XXXV
Mean values of yield of seed-cotton in maunds per acre.
Varieties Year S,E. ±
---.-~.-------~---
4F 'Victory'
Critical difference at 5% :t:
------- ---.. -~--- .. ------ ~,,------- ---------- --~ .. ---
1943 1944
6.63 7.91
5.56 6.23
0.224 0.202
One rnaund=82,28 pounds avoirdupois.
0,636 0.572
It is clear from the above Table that 4F gave a significa:1tly higher yield than 'Victory' in both years.
(ii) Dates of sowing
The effect of date of sowing was significant during both the years and the results are presented in Table XXXVI.
Year
1943 1944
TABLE XXXVI
Mean yield of seed-cotton in maunds per acre.
14/5
5.82 8.37
Dates of sowing
4/6
S.E. ± Critical
difference
25/6 I at 5% :±: ~~~~~ ----- ~------- -----~----
8..95 10.28
3.52 2.57
Non-significant 0.202 I 0,794
Order of yield ;-
1944 II Sowing TSowing III Sowing The results were somewhat different in the two years. WhIle the highest
yield was always recorded from the second sowing and the lowest from the third sowing the yields from the three dates of sowing were absolutely distinct from one another in 1944.
EFFECT OF AGRONOMIC FACTORS ON JASSID POPULATION fi3
It must also be mentioned that the last sowing date gave such a poor yield that it must be discarded in the popular agricultural practice. Dastur (1944) has recommended a sowing period for Lyall pur extending from 25th of May to 20th of June. According to the present results it appears that the sowing time in Lyallpur should not be extended beyond about the middle of June.
(iii) Spacings
The effc!ct of spacing on yield was highly significant in both the years. Th~ results are given in Table XXXVII.
Year
I' X I'
TABLE XXXVII Mean yield of seed-cotton in maunds per a;re.
Spacings S.E. ±
l' x 2' 2/ >:3'
Critical difference at5% ± i 1 x 3' I 2' x 2' i
-- - _______ ~l-___ 1-----. ----
i I --------;---------
I 1943 1944
7.86 9.05
6.43 7.31
1 6.10 1 5.50 I .
7.22 6.37 3.05 5.42
0.354 0.320
1.005 0.908
Order of yield :-
1943 -i''Xl' l' x 2' I' x3'
1944 -Y'xl' l'x2' l'x3' 2')'.2' 2'x:V The yield is, thus, seen to decrease progressively from the dosest to the
widest spacing. (iv) Interaction between varieties and spacings
This interaction was non-significant in both the years and hence it will not be discussed.
(v) Interaction between varieties and sowing dates This interaction was significant during 1943 o;)ly, but the figures of both
years are given in Table XXXVIII. TABLE XXXVIII
Mean yield in maunds per acre.
I Dates of sowing I Critical I Year Variety I S.E. ± difference
I 14/5 4/6 25/6 at 5% ±
1-- _-_. _ _ ._----
1943 4F 5.27 10.04 4.58 I
0.388 1.100 'Victory' 6,38 7.86 2.45
1944 4F 9.26 11.15 3.33 'Victory' 7.49 9.40 1.81 Non-significant
64 COTTON ]ASSID IN THE PUNJAB
It will be seen from Table XXXVIII that the second sowing gave the highest and the third sowing the lowest yield in both varieties in both the years.
(vi) Interaction between spacings and sowing dates
This interaction was significant in 1944 only. The mean values of yield
are given in Table XXXIX. TABLE XXXIX
Mean yield in maunds per acre.
I Date Spacings Critical Year of S.E. ± difference
!sowing ~~-y~; ~-2' l' X 3' 2' x 2' \ 2' X 3' at 5% -I-
-·--i--- _.---- _-- ---.~- --_._. !
1943 i 14/5 6.81 5.79 5.65 5.77 5.09 Non-significant I 4/6 11.60 9.55 9.28 7.74 6.58
25/6 5.18 3.94 3.36 2.99 2.11 1944 14/5 10.46 7.70 8.51 8.31 6.88 0.554 1.572
4/6 12.94 10.81 11.03 8.95 7.66 25/6 3.75 3.40 2.12 1.84 1.72
It will be seen from Table XXXIX that the yield decreased consistently from l' X I' to 2' X 3' in both the years and in almost all the sowing dates.
(vii) Interaction oj second order All these interactions were non-significant and will, therefore, not be
discussed. (viii) The yield of seed-cotton and the jassid population will now be con
sidered together. The effect of agronomic factors on yield and jassid population are depicted side by side in Table XL.
Before any comment is made on this Table, it is necessary to recall that 1943 was a year of very mild jassid attack while in 1944 the attack was very high indeed. It can, therefore, be ar~ued that the effect of jassid attack on yield will be more pronounced during 1944 than in 1943.
Now looking at the Tables of yield (Table XXXV to Table XXXIX) it is seen that the yield in 1944 was throughout higher than in 1943. This was contrary to general expectation and is probably due to the better quality of soil and favourable weather conditions for the crop. It was seen that although the rainfall in 1944 (10.80 / ) was only about an inch more than in 1943 (9.87"), yet its distribution was much better in 1944 than in 1943. In the latter year there were only six measurable showers while there were eight such showers in 1944. Thus, whatever the jassid population, the cotton crop on better soil and under more favourable weather conditions will give a higher yield.
Coming on to Table XL it will be noted that while the yield varied inversely with the jassid population in different spacings, this inverse relationship was
EFFECT OF AGRONOMIC FACTORS ON ]ASSID POPULATION 65
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66 COTTON JASSlD IN THE PUNJAB
not maintained in case of the sowing dates. It will also be seen that, in the year 1944, the yield of the crop was the highest in second sowing (4/6) in spite of the fact that the jassid population in this sowing was higher than that in the first sowing date (14/5). In the year 1943 also, the first rank of the second sowing as regards yield was also fully maintained, though statistically the results dUJ;ing tbis year were non-significant. On the basis of the' results of the two years, therefore, it can be argued that the sowing of the crop at the optimum time has more potent effect on the yield than the jassid population.
Causes of variation in jassid population in different varieties, dates cf sowing and spacings
That certain agronomic factors affect the jassid population is now well known and the experiments described so far in this chapter fall into line with the experience of other workers that the mue chlnge in date of sowing or spacing will affect the jassid population to a very marke~] degree.. 'I:'he previous workers, have, however, not made any attempt to find out the basic causes, if any, of the variation in jassid population due to these changes in the agronomic practices. Such an attempt was made for the first time in 1944 and a brief aCCOJ..lnt of these experiments will not be out of place here.
From a priori considerations the following three characters of the plant were considered to be mOre important than others and were studied in detail. Tt.ese characters are more directly associated with egg-laying and hence the population of the insect.
(a) Moisture percentage of the leaf-vein. (b) Hairiness of the leaf-vein. (c) Toughness of the leaf-vein. "
The details of method of estimating these characters are dealt with elsewhere. It may only be mentiond here that the moisture percentage of the leafveins was determined after every ten days from primary leaves of 22 days' age. The hairiness of the veins was determined on leaves from the 10th,' 20th, 25th, 30th, and 35th node at the a.ge of 22 days. One centimeter length of the three prominent veins of each leaf from the pulvinus spot was taken into consideration. The toughness of veins was measured by a special apparatus the details of which appear elsewhere.
The figures obtained for these three characters were analysed and the final results of the analysis of variance are discussed below :-
(a) Moisture percentage
The two varieties had significantly different moisture percentage as shown below:-
. Varieties Moisture percentage S.E. Critical difference at 5%
4F 79.2849
± 0.1596 ± 0.4424
, Victory' 80.5301
EFFECT OF AGRONOMIC FACTORS ON ]ASSID POPULATION 67
4F which had a definitely lower ja.3sid population than 'Victory' :hdd similarly a significantly lower moisture percentage.
The effect of sowing date on moisture percentage was non-significant. The mean values of moisture percentage for different sowings were :-
Sowing dates 14/5 4/6 25/6 Mean moisture percentage ... 81.1713 78.8954 79.5558
The effect of spacing on moisture percentage was significant, the mean values and their standard error being :-
Spacings Moisture percentage
S. E.
i'Xl' 79.0251
± 0.2524
Critical difference at 5% ± 0.6995
I' x 2' l'~~i';)(2~'-X3'
. 79.8508 80.0276 80.2150 80.4190
Here againit will be seen that the moisture percentage in different spacings ran practically parallel to the jassid population figures.
All the 1st order interactions were non-significant and will not be discussed but it must be stated that, in general. jassid population followed closely the moisture percentage of leaf-veins. This confirms the findings of Mumford and Hey (1930) that disturbed W:l.ter balance from whatever calise rendered the cotton plant more sllsceptible to the attack of sap-feeding insects.
(b) Hairiness of leaf-veins
The difference in the hairiness of leaf-veins of the two varieties was statistically significant as shown below:
Varieties Mean No. of hairs in one em. of leaf-vein S. E. Critical difference at 5%
4F 263.65
± 2.986 ± 8.476
'Victory' 46.28
4F had a significantly larger number of hairs than 'Victory' and the jassid population was in the reverse order, being high in 'Victory' and very low in 4F.
The hairiness of leaf-veins did not vary significantly in the three sowing dates and therefore the figures are not reproduced here.
The effect of spacing on hairiness was, however, significant and the mean values and their standard error are given below :-
Spacings l' X l' l' X 2' l' X 3' 2' x 2' ~·--2' x 3'
Mean No. of hairs 182.543 153.802 143.619 133.845 123.609
S. E. ± 4.7201 Critical difference at 5 % :±:13.397
68 COTTON JASSID IN nIE PUNJAB
These figures show a definite decrease in hairiness with the increase In
spacing and the order of hairiness corresponds with jassid population In
a reverse direction.
Though the difference in hairineIOs in the different sowing dates was not significant, the interaction of varieties X sowing dates was highly significant. The mean values of hairiness for varieties and sowing dates are given below :-
TABLE XLI
Mean number of /win per centimeter of leaf-vein.
I Mean hairiness in different sowings S. E. Critical
Varieties ---~~I
± difference
14/5 I
4/6 at 5% ::!:
--~--~----- __ -
4F ... 260.620 250.338 234.998 5.171 14.676
'Victory' ... I
39.780 47.050 I
51.997 Non-significant
It is of interest to note tha t in the hairy variety (4F) the hairiness decreased progressively in the later sowings while in 'Victory' there was a progresslve mcrease. No explanation can be offered for this differential response of the two varIeties. The jassid population, however, increased with later sowings in both the varieties.
The interaction of varieties X spacings was also highly significant and the mean values of hairiness are given below:
TABLE XLII
Mean number of hairs per centimeter of leaf-vein.
I Mean hairiness in different spacings Critical S. E. differ-
Varieties
I ± ence at
l' X l' I'X2' 1'x 3' 2' X 2' '2x3' 5% ± ----_---- ----_---- ~-.--.--,--- , . -"--""
4F
"'1 303.700 264.604
I 244.717 223.772 206.469 26.675 19.446
'Victory' ... 61. 387 I 43.002 I 42.322 43.919 I 40.750 Non.significant \
It will be seen from the above figures that in both the varieties closer spacings had a larger number of hairs than the wider spacings. The jassid population was in the reverse order.
EFFECT OF AGRONOMIC FACTORS ON JASSID POPULATION 69
(c) Toughness of leaf-veins
The difference in the toughness of leaf-veins of the two varieties was highly significant. The figures are given below :-
Varieties --zy-Mean toughness 60.185 S. E. ± 0.3388 Critical difference at 5% :±: 0.964
The leaf-ve_ins of 4F were significantly tougher than those of 'Victory.' The jassid population was also significantly lower on 4F and higher on 'Victory.'
The effect of date of sowing on toughness was also significant. The ngures given below show a tendency for toughness to decrease with later sowings.
Dates of sowing 14}5 4J6 -25/6 Mean toughness 60.146 58.324 49.498 S. E. ± 0.398 Critical difference at 5% ::l: 1.563
It has already been seen that jassid population increased in the later sowmgs.
The effect of spacing on toughness was highly significant and the results are interpreted below :-
Spacings Mean toughness S. E. Critical difference at 5 %
l' X I'
57.913 -t- 0.5357 ± 1.5205
l' x 2' l' x 3' 57.413 55.648
2' x 2'
54.998 2' x 3'
54.141
It will be seen that there was a progressive decrease in toughness of leafveins with wider spacings and it has already been shown that the jassid population increased with wider spacings.
The interactions were all non-significant and will, therefore, not be discussed.
In order to bring out the association between jassid population and three plant characters dealt with a bove the statistical significance of the results were tabulated and are given in Table XLIII.
The variation in jassid population in the two varieties under different agronomic treatments may now be explained.
'Victory' had significantly larger population because it was distinctly less hairy and its veins had more moisture and were softer than those of 4F. The impediments to egg-laying were, therefore, far lecls in 'Victory' than in 4F.
As for dates of sowing, the governing factor was, perhaps, only the toughness of leaf-veins. The leaf-veins became progressively tougher with the earlier sowings and, therefore, the population also decreased with the earlier sowings.
70 COTTON JASSID IN THE PUNJAB
TABLE XLIII
Causes of variation ill jassid population in the complex experiment, 1944.
Characters
Varieties '"
Dates of sowing.
Spacings
Varieties· X spacings.
Varieties x sowing dates.
Sowing dates X spacings.
I SIGNIFICANCE OF RESULTS
1- -.-.--.----.------.------ --.------- ----- --------.. ----
I
· }assid popu;lation I Moisture p~rcen- Hairiness of veins
Toughness of veins by countmg ; tage of VelllS
Il~'!~ttl~y,~o:~gth~~ '~!~ttl?~or~igthi~~ . '~!~~t~~-y-' l-e-s:-igth~fi:- '~i-·~-~l-~-y'-l::;g-;h-ia-fi~-~ ~ ~ ~
IIT and II sowing Non-significant... Non-significant ... significantly high-
III sowing significantly less than II and Il significantly less than I
er than I sowing
2' x 3', 2' x 2', l' )( 3' and l' X2' significantly higher than l'x I'
2' X 3',2' X 2', l' x 3' and l' x 2' significantly more than l' x. l'
Non-signifi.::ant... Non·significant ...
Significant dec- Non-significant ... rease in both var-ieties from I II to I sowing
Non-significant Non-significant ...
Consistent increase from 2' X 3', 2' x 2' I'X3',1'x2' to l' x l'
2' x 3', 2' X 2' and 1'): 3' significantly less than 2' Xl' andl'Xl'
A general increase Non-significant in both the varie-ties from 2' X 3', 2' X2',I' x 3',1' x 2'i tol'xl' I
Constant increase Non-significant from III to I sow-ing in 4F and re-verse in 'Vic-tory'
Non-significant Non-significant
It was seen that closer spacings had lesser population. In this case all the three plant characters, moisture percentage, hairiness and toughness were affected and it must be assumed that all the three played a part in regulating the jassid population.
Nothing much need be said here about the interactions of the factors mentioned above but it will be clear from Table XLIII that the hairiness of the leaf-veins appears to have played the predominant part in determining the jassid population.
It is not possible to assess the relative importance of the three plantcharacters under discussion in modifying the population, but since hairiness was significant in most cases, it must be assumed that this was the most important plant-character which was concerned in determining the extent of infestation.
EFFECT OF AGRONOMIC FACTORS ON JASSID POPULATION 71
j treet of irrigation on jassid population
A difference in the number of irrigations given to the cotton crop is likely to affect the micro-climate in the vicinity of the plants and, therefore, the jassid population may also vary. To test this point the jassid population was estimated from irrigation experiments. During 1941, irrigation experiments were. laid out with 289F/43 and L.S.S. with light (first watering 6 weeks after sowing and subsequent irrigations after every 4 weeks), medium (standard irrigational practice of the tract) and heavy (first watering 3 weeks after sowing and subsequent irrigations every fortnight) irrigations. There were three replications
and jassid population was determined by sweeping. The results are given in Table XLIV.
Year Scale
1941 Log (n+1) Antilogs
1942 Log (n+1) Antilogs
S.E. for 289F /43
S. E. for L.S.S.
TABLE XLlV
Mean jassid infestation (log n+I).
289F/43 L.S.S. ----;---------1----- ... _-.------
I Heavy Medium Light Heavy !Medium i Light I
I 1.862 1.638 1.536 I 2.033 I 1.776 I 1.685 , 71.78 42.45 33.36 106.90 \58.70 )47.42
2.036 1.885 I' ,
1.854 2.184! 2.060 I 2.075 107.60 75.74 70.45 151.80 \113.80 117.90
1941
1942
1941
1942
±0.0371
±0.0288
±0.0493
±0.0398
Significant
Significant
Significant
Non-significant
The order of infestation was as below: -
289F/43 L.S.S.
1941 Light
1942 Medium
It will, thus, be seen that, in general, heavy irrigations were conducive to a higher attack of jassids. The results were, however, more pronounced in 289F/43 than in L.S.S.
During 1943, two experiments were laid out to determine the effect of irrigational treatments on the incidence of jassid attack. The variety of cotton
72 COTTON JASSID IN THE PUNJAB
under both these experiments was L.S.S. sown in randomized blocks. Observations were carried out on three replications in each case and jassid population was estimated both by sweeping and counting.
Experiment No. r. D~tferent number of irrigations :-The number of irrigations varied from 3 to 8 and each irrigation was 3" deep. The results of statistical analysis are presented in Table XLV.
TABLE XLV
Mean jassid population per bed.
M,thod I &,1, I No. of '''',,''on, Standard I Critical error difference
7 8 ± a~ 5%±
c I 3 4 5 [ 6
ounting \ Log(n+;)~ 1.1251 1.144~ 1.2040 '~1.2053 1.2253 1.2981 0.0283 0.0835
s Antilogs ... 12.23 12.94 15.00 15.04 15.80 15.86 ... ...
weeping I Log(n+1) ... 1.0553
1
1.0898 1.0676 1.1598 1.1265 1.2257 0.0249 0.0867 Antilogs ... 10.36 11.29 10.69 13,45 12.39 15.82 ... ...
Order of infestation :-
Counting 3 4 5 6 7 S
Sweeping 3 5 4 7 6 8
It will be seen from Table XLV that, as ascertained by counting, the
population showed an increase in plots which received a larger number of irrigations.
In order to determine the trend of increase in population, the sum of squares due to treatments (irrigations) were spli t up and the results are depicted in Table XL VI.
TABLE XLVI
Splitting up of sum of squares due to irrigations.
D.F.I I
Due to 8.S. M.S; F. Remarks
~---.--.. ----- -I .-
IRRIGATIONS:
Linear ... 1 0.09071384 0.09071384 22.628 Highly significant
Quadratic ... 1 0.00049140 0.00049140 0.122 Non-significant
Cubic ... 1 0.00236423 0.00236423 0.590 Non-significant
. Residual ... 2 0.00423845 0.00211922 0.529 Non-significant
Error ... 20 0.08017806 0.00400890 '"
I ...
EFFECT OF AGRONOMIC FACTORS ON JASSID POPULATION 73
It will be noticed from Table XLVI thlt the lineJ.r regression alone was significant. This means that the jassid popuhtion increased from 3 to 8
,! irrigations in a linear manner. Almost the same results, with only slight differences, were obtained by
sweeping. Experiment NO.2. Frequent light and less frequent heavy irrigations : -The
total quantity of irrigation water applied was 20 acre inches but it was given in
3, 4, 5, 6 and 8 irrigations. The mean jassid population in the different beds is given in Table XLVII.
TABLE XLVII
Mean jassid population per bed.
Method Scale No. of irrigations
----------- -----~-----__ ~_J_4 __ 5 ___
1
___ 6 __ 1 ___ 8 __
Counting Log (n+1)
Antilogs
Sweeping Log (n+1)
Antilogs
i 1.1288 \ 1.06411 1.1739
12.45 '10.59 13.92
1.1028
11.67
1.1548 1.1821 I
13.29 114.21
1.1933
14.61
1.1269
12.40
1.1620 11.1931
13.52 14.60
The results obtained both by counting and sweeping were non-significant.
It will be seen from the results of these two experiments that the variation in jassid population was significant in Experiment No.1, where 9 acre inches to 24 acre inches of water were applied. It ca n, therefore, be inferred that, on the whole, heavier irrigations may, within certain limits, induce a heavier attack of j ass ids but if the quantity of water remains the same, although the number of irrigations may vary, the jassid population remains unaffected. The Punjab cultivators have perforce to give fairly constant quantities of water to their cotton crop every year (the normal being six irrigations) according to their fixed water turn from the canal. This factor may, therefore, be ruled out as an agronomic practice affecting the jassid population in the general cotton
crop of the province.
CHAPTER XI
THE NATURE OF RESISTANCE
The population of E. devastans on different varieties of cotton in different years and localities and under different environmental conditions has been discussed in detail. It has been shown that some varieties have consistently lower population than others under an identical set of conditions. Such varieties with lower population are termed as more resistant than those which harbour a higher population. Considering an extrem::: cage, the desi (G. arboreum) varieties of cotton have, under all conditions, an extremely low population or none at all. These varieties are, therefore, called immune varieties. It is now proposed to study the nature of resistance and the factors which bring about resistance in plants, as such knowledge is an essential prerequisite in the production of resistant varieties.
In order to study the fundamental nature of the factors responsible for resistance, development and oviposition studies of E. devastans were carried out on bhindi (Hibiscus esculentus) which is the mast favoured host plant and the American and desi varieties of cotton.
Egg-laying by females of E. de'lJasians
A large number of fresh young leaves of bhindi and several varieties of cotton, both American and desi, were enclosed in voil sleeves to prevent promiscuous
egg-laying on them. Later, when the leaves were well developed a certain number of jassid females which had been bred in the laboratory and which had not laid any eggs previously, were liberated on the leaves under vail sleeves. These females were given fresh !e3.ves after every 24 hours to help them to lay the largest number of eggs. The leaves which were exposed to the females for egg-laying were then plucked off the plant and the number of eggs laid on them was counted by dissecting the veins under a binocular (Verma and Afzal, 19+0). The average number of eggs laid by one female on different varieties is given in Table XLVIII.
It will be seen from Table XLVIII that very few eggs were laid on the desi varieties while a comparatively much larger number was laid on the American varieties. Amongst the later group, a clear distinction can be made between the resistant and the susceptible varieties, as a relatively larger number of eggs was laid on the latter as compared to the former varieties. Bhindi stands in a class by itself. The number of eggs laid on it is very much larger than on any variety
THE NATURE OF RESISTANCE 75
of cotton. This appears to be the chief reason of the very high infestation of E. devastans on bhindi.
T ABLE XL VIII
No. of eggs laid on bhindi und different varieties of cotton.
Average No. of eggs laid per female
N arne of variety Field notes on resistance
1937 1938 1939 -------,_ ... _--_._-- ,----- -
39 Mollisoni 1.40 0.82 1.59 Immune
Jubilee 1.66 1.18 Immune
4F 7.05 3.85 Resistant
L.S.S. 6.63 4.50 5.25 Resistant
289F!43 6.71 3.92 4.64 Resistant
'Victory' 9.94 Susceptible
38F 9.57 6.62 Susceptible
289F/K.25 7.25 11.98 Very sU5ceptibie --, __
~--- ~--.-----.. - -----_---
Bhindi 12.57 29.08 Most susceptible
Note ;-The names of desi varieties appear in italics.
Hatching percentage of eggs In order to pursue this enquiry further the hatching percentage of eggs WaS
determined. It may be possible that, as in the case of egg-laying, there may be varietal differences in egg hatching in different varieties. Eggs laid in the leafveins of some varieties may not be able to hatch out propzrly owing to the texture or the chemical composition of the veins. " ,
Equal number of gravid jassid females were liberated, as in the case of egglaying experiment, on leaves of bhindi md different varieties of cotton. Th~ leaves were carefully watched and the number of nymphs hatched were coudte'd. The unhatched eggs were later counted by dissecting the leaf-veins. The egg shells from which nymphs have emerged become transparent and cannot be distinguished from the leaf-tissue while the unhatched eggs could be made o~t for some time due to the presence of the yolk in them. The results obtained ar'e given in Table XLIX.
76
Variety
39 Mollisoni Jubilee 4F L.S.S. 289F;43 'Victory' 38F 289F;K.25
Bhindi
COTTON JASSID IN THE PUNJAB
TABLE XLIX
Hatching 'percentage of eggs of E. devastans.
Hatching percentage Field notes on resistance
1938 1939 -_ --- ----
100.0 92.3 Immune 100.0 Immune 94.3 Resistant 96.6 95.3 Resiatant 97.4 93.0 Resistant
94.0 Susceptible 99.2 Susceptible 98.6 93.4 Very susceptible
98.4 92.7 I Most susceptible I
These two years' figures show that there was absolutely no difference in. hatching percentage on different varieties of cotton or bhindi and the eggs once laid even on immune varieties of cotton hatched out normally.
Development of nympbs To carry the argument a step further, the development of nymphs was also
studied. An equal number of first instar nymphs was collected from bhindi several times in the season and these were caged on different varieties of cotton. The leaf area offered for each variety was approximately the same and the number of nymphs which ultimately developed into adults was counted. These data are presented in Table L.
TABLE L Nymphal development on cotton and bhindi.
Variety Percentage of nymphs which developed into adults
1937 1938 1939 1940 --_--_ ----_ ... _-----
39 Mollisoni ... 77.3 66.3 58.5 63.5 Jubilee ... 77.5 80.6 . .. ... 4F ... 79.8 86.9 71.6 ... L.S.S. ... 76.7 86.9 72.1 73.5
. 289F/43 .. 80.0 83.1 80.4 66.9 'Victory
, 91.7 89.1 ... ... .. .
38F .0. 81.3 84.1 ." ... 289F/K.25 '" '" 86.9 86.2 71.7
.---.. -.--~ -
Bhindi ... ... .. . 85,4 78.3
THE NATURE OF RESISTANCE 77
The figures in Table L show that the nymphs could feed and develop into adults practically equally well on the most favoured host plant, bhindi and all varieties of cotton, whether immune or highly susceptible.
From the experiments detailed above it may be concluded that: -
(i) There is a marked reduction in the number of eggs laid by the jassid females on desi cotton and other resistant American varieties.
(ii) The number of eggs laid vary with the different host plants. The highest number of eggs was laid on bhindi and this was probably the reason of this plant being most s~verely infested.
(iii) J assid eggs when once laid even on immcme varieties of cotton have no difficulty in hatching, and,
(iv) Jassid nymphs can feed and develop into adults equally well on bhindi and different varieties of cotton.
It is, thus, clear th1.t the causes of resistance or susceptibility of different varieties of cotton must be sought in the structure and physiology of the leafvein. The factors which hinder oviposition will induce resistance in the plant, while those which render oviposition easy and profuse will go to make the plant susceptible. The whole question of resistance or susceptibility, therefore, revolves around oviposition which in its own turn depends on the structure and physiology of the leaf-vein. A detailed study of the leaf-vein was, therefore, undertaken.
CHAPTER XII
CHARACTEkS OF TBB LEAF-VEIN ASSOCIATED WITH RESISTANCE
In this study attention has, so far, been confined to the following charac-lers (Afzal and Abbas, 1943) :--
(a) Thickness of the cuticle;
(b) pH value of the cell sap j
(c) Moisture contents of the leaf-vein;
(d) Toughness of the cuticle; and
(e) Hairiness of the· leaf-vein.
'These characters will be dealt with seriatim.
Thicknes~ of the cuticle
Cross-sections of the leaf-veins of resistant and susceptible vanetIes were exa~ined, but no clear-cut differences in the thickness of the cuticle, the extent of inter-cellular spaces, or the secondary thickening of the cell walls Were found. This character must, therefore, be ruled out as affecting resistance in any way.
pH value of the cell sap
The acidity of the cell sap may render it unpalatable to the insect which will consequently avoid such plants for feeding, and possibly, also for egg-laying.
Sloan (1938) considered the acidity of the cell sap as a factor involved in conferring resistance. Afzal Husain and Lal (1940), on the other hand, found no correlation between the acidity of the leaf juice of the Punjab-American varieties and their susceptibility to jassids.
Full-grown leaves (22 days old) of bhindi and several varieties of cotton from approximately the same nodes of the main stem were taken and the cell sap was extracted. The pH value of the cell sap was determined with the help of a pH micrometer and the data obtained are given in Table LI.
It will be seen from Table LI that there was no clear-cut association between the pH value of the cell sap and jassid resistance. Thes~ results thus Ilupport the findings of Afzal Husain and Lal (1940).
CHARACTERS OF THE LEAF-VEIN ASSOCIATED WITH RESISTANCE 79
TABLE LI
pH value of bhindi and some varieties of cotton, I941.
199 F 139 Malli-i sani __ ~a_t~ of obse~vation I_B:i~~_I~~~2~1 1_~Victo~12S9 F/+311.~s.s~
---1---1 !
July 28... i 5.88 5.59 5.67 /' 5.76
August 9 ...! 5.83 5.56 5.+1 5.68
August
September
Septcmber
19
1
9
September 20
October
October
1
9
! ... i 5.97
6.18
6.30
6.00
5.56
5.96
S.H
5.89
6.68
6.79
5.47
5.83
5.84
5.61
6.11
5.50
5.91
5.99 \
5.91 II
6.33
5.80
5.4-2
5.63
556
5.76
5.80
5.83
5.88
5.57
5.72
5.67
6.28
6.18
5.78
6.40
6.68
5.81
5.67
5.51
5.70
5.74-
5.77
----------- __ .. -._ 6.95 I 6.86 I
-'----_.'---" _-_. __ ~--- _--_._-_ --. h' . I Ant metle mean ... I 6.027
--. --I Nature of the plant I Most
susceptible
5.971 5.861_ ~~~~ _. 1_5._71_0 _I 6.035
Very Suscep- Resistant suscep-I tible I tible I
Resistant Very resistant
S. E. = ±O.0837
5.700
Immune
o rde r of pH va I u e : - ~,.....:--:-::=o"-::-::-:-:-;".,..,.::--::-:="",,r-:oc:----7i:==;:=-:;=-Bhindi 199F 289Ft4-3 289FjK.25 'Victory' 39 Mallisoni L.S.S.
Moisture contents of the leaf.veins
It has been observed in the Punjab that plants with a leathery texture of the leaves appear to be resistant to jassids. It was supposed that the leathery texture of the leaves was associated with a lower moisture content. Since, however, the focus of jassid infestation is the primary veins of the leaves, their moisture contents were determined. The thick prominent portions of primary veins were cut out from 5 to 8 fresh leaves of 22 days age at different dates. These were dried in a steam oven and the moisture contents were determined. The data are given In Table LII.
It will be seen from the figures given in Table LII that in both the years the desi varieties had the lowest moisture content. Amongst the group of American varieties. the moisture percentage was usually higher in the susceptible varieties and lower in the resistant ones. Bhindi stands out prominent 10
having a significantly higher moisture percentage than all varieties of cotton in both years.
This experiment was repeated during 1943 with only two varieties, 4F and 'Victory', which are respectively very resistant and susceptible. In this case also full-grown leaves were taken nine times during the season at an interval of
80 COTTON ]ASSID IN THE PUNJAB
N '-0 U"") U"")
o o +1 +1
I~
I~ ?
I:;
I~ 11
CHARACTERS OF THE LEAF-VEIN ASSOCIATED WITH RESISTAN(;E 81
10 days and the moisture percentage of veins was determined. These figures are given in Table LUI.
TABLE LIII
Moisture percentage of leaf-veins.
No. of observations
Moisture percentage
1 2 3 4 5 6 7 8 9
I 1------81.857 84.414 82.565 82.028 77.780 76.744 70.621
4F
I
i 73.807 71.763
--M-ea-n----i _--. ·--77~~;··-------
--_.----'Victory'
82.740 84.682 83.132 81.866 79.392 79.143 74.920 76.645 76.019
79.838
Standard error :t 0.3930 Critical difference at 5% ± 1.2817
Order of varieties 4F 'VlctorT
The figures given in Table LIlI show that the varietal differences in the moisture percentage of the leaf-veins were significant up to 5% level and that the resistant variety had significantly less moisture in the leaf-veins than the susceptible variety. Although the effect of replications was non-significant, yet the trend towards lower moisture contents with the advance of the' season is quite
clear. It may also be mentioned that the moisture percentage of the leaf-veins was
closely associated with rainfall or irrigation. The application of water to the field through natural precipitation or irrigation or both, within a week of sampling, affected the moisture percentage, and this is the reason for the disparity between the figures of two years given in Table LII. The same is, probably, the cause of the fall in moisture percentage towards the end of the season in all the three years. There was no rain after 20th September and irrigations were stopped after 15th October. The moisture percentage of the leaf-veins decreased appreciably due to the desiccation of the soil.
It must, however, be mentioned that on account of the variation in moisture percentage due to irrigation and precipitation and the slowness of the actual
82 COTTON JASSID IN THE PUNJAB
process of determination, this method of assessing the jassid resistance of cotton plants is unsuitable on a breeding station.
Toughness of the cuticle
For the first few years the search for a delicate apparatus to measure the toughness of the leaf-veins proved fruitless. The apparatus used by Jewett (1933) for dovers and Boyce (1933) for walnut were found to he unsuitable. Later on the apparatus designed by Dr. Nazir Ahmad, Director, Technological Laboratory, Indian Central Cotton Committee, Bombay, was found to he suitable after small modifications. A photograph of the apparatus is given in Fig. 5.
The instrument consists of a freely pivoted needle-point which rests on the cuticle of the leaf-vein mounted on a base-plate. The other end of the lever supporting the needle is connected by means of a strong, non-elastic string to a hydrostatic float of the O'Neill's fibre strength tester. The float could be either raised or lowered by regulating the quantity of water in the cylinder in which the float was freely suspended.
To start with, the tension applied to the needle-point was zero. As water was withdrawn, a gradually increasing pressure was brought to bear on the leafvein. When the pressure was high enough to overcome the resistance of the cuticle of the leaf-vein, the needle-point pierced through the cuticle, with a sudden and visible jerk. The volume of water withdrawn from the cylinder up to this point was an index of the resistance of the leaf-vein to the needle-point.
Exploratory work on this character was done during 1943, and the F4 hybrid progenies of the following two back-crosses, which were splitting for hairiness, were examined in detail (Afzal and Ghani, 1948).
Progeny No. 204 of (920 Cambodia X S8F) 289Fj43 and Progeny No. 226 of (920 Cambodia X S8F) 'Victory.'
The primary leaves of all the plants in these two progenies were examined for toughness and hairiness. In this way 75 plants were dealt with. The toughness of the middle vein at a distance of one cm. from the pulvinus spot was determined. The average nymphal population of jassid on the entire plant was also recorded. The data are given in Table LIV.
COTTON JABSID IN THE PUNJAB
Fig. 5.-Apparatus for testing the toughness of leaf-vein.
CHARACTERS OF -THE LEAF-VEIN ASSOCIATED WITH RESISTANCE 83
TABLE LIV
Nymphal population and mean hairiness and toughness in hybrid progenies.
ci z Prqgeny No. 204 Progeny No. 226
----.,-~---.------
q I cd Population Hairiness Toughness Population Hairiness Toughness
- ----.-~- -
1 256.83 9.67 56.00 77.83 36,25 I 67.10 2 133.46 116.58 85.08 77.2,5 183.75 i 71.39 3 139.21 156.83 80.71 155.04 21.92 I 66.33 4 115.66 87.33 79,19 110.88 49.67 I 69.56 5 237.41 24.75 48.92 119.67 27.75 64.36 6 136.62 52.58 80.72 115.08 34.17 63.80 7 202.66 30.33 59.29 68.04 232.67 65.90 8 266.08 11.92 55.44 67.92 45.83 61.15 9 118.96 96.25 73.72 81.17 61.50 57.58
10 62.08 107.25 66.89 59.54 160.42 67.92 11 123.00 70.00 76.19 110.67 21.75 60.15 12 57.67 82.92 72.75 108.38 20.58 60.50 13 62.25 130.75 67.25 69.54 44.00 48.72 14 302.62 5.08 55.60 94.58 36.50 58.14 15 174.33 6.92 51.50 45.13 195.42 66.94 16 118,37 129.58 77.89 114.67 38.00 53.73 17 184.33 151.17 67.06 121.88 15.33 61.85 18 214.66 104.00 70.75 49.54 190.08 62.00 19 171.16 12.67 56.63 97.54 35.50 74.29 20 _ 50.29 148.00 62;00 105.33 33.50 66.13 21 135.21 109.33 72.50 62.54 122.58 67.00 22 112.00 112.83 74.50 62.33 161.33 69.00 23 94.12 79.50 67.69' 58.13 182.50 64.13 24 58.29 103.50 68.70 . 43.42 180.92 70.55 25 127.33 105.92 68.75 77.54 24.33 61.00 26 158.83 98.33 59.00 103.92 34,67 52.29 27 60.62 84.25 70.36 54.67 142.75 61.61 28 88.83 86.00 81.25 82.42 50.67 60.67 29 79.08 114.75 63.70 113.46 37.33 65.42 30 46.25 117.83 62.50 116.04 37.00 69.25 31 79.75 79.75 78.96 45.21 208.25 65.61 32 65.67 191.92 76.10 41.33 199.92 68.00 33 94.96 97.83 72.33 107.67 30.42 58.83 34 84.25 106.33 71.67 59.83 224.75 70.79 35 70.54 123.25 79.00 84.92 47.00 70.40 36 205.83 7.17 56.86 75.42 75.33 63.45 37 68.71 109.58 65.00 42.04 194.50 66.58 38 103.50 128.42 82.81
I ... ... ....
84 COTTON JASSID IN THE PUNJAB
The correlation coefficients of these three characters worked out ftom Table LIV are given below :-
Hairiness and toughness
Progeny No. 204- r = +0.6050 Significant at 1 % level Progeny No. 226 r = +0.4022 Significant at 1% level
The correlation was positive and significant in both cases, showing thereby that the more hairs there are on the leaf, the tougher its veins are likely to be.
Population and tougbness
Progeny No. 204 r = - 0.5295 Significant at 1 % level Progeny No. 226 r = - 0.1899 Non-significant
This correlation was significant only in the case of one progeny and its validity should, therefore, be considered as somewhat doubtful. The negative nature of this correlation in both the progenies, however, indicated that the jassid population had a tendency to decrease as the toughness increased.
Hairiness and jassid popUlation
Progeny No. 204 r - 0.6873 Significant at 1 % level Progeny No. 226 r = - 0.8108 Significant at 1% level
The correlation coefficients in this case are very high and significant and show that hairy plants have definitely a smaller population than the less hairy
jones.
In order, however, to work out the inter-relationship of these three characters, population, toughness and hairiness of the leaf-vein, partial regressions were worked out as it is only by this method that the actU3.l relationship can be found
out. The partial regressions of toughness and population by keeping the hairi
ness as constant were :-
Progeny No. 204 r Progeny No. 226 r
= - 0.1966 Non-significant + 0.2542 Non-significant
Thus, it a ppears that toughness alone plays a very small part in determining the jassid population on a plant. The partial regressions of hairiness and population by keeping the toughness as constant were as follows :-
Progeny No. 204 r - 0.5434 Significant at 1% level
Progeny No. 226 r = - 0.8171 Significant at 1% level
Both these regressions are negative and highly significant, which means that
as the hairiness increases, the jassid population decreases.
CHARACTERS OF THE LEAF-VEIN ASSOCIATED WITH RESISTANCE 85
It must also be suggested that delicate measurements of toughness will not prove of much benefit to the plant breeder unless such measurements can be made very rapidly. The breeder has to deal with, literally, thousands of plants in a short space of time and it is necessary that some easily recognisable morphological character of the plant associated with resistance must be found out. From the partial regressions given above, it appears that hairiness might prove to be such a character and this character was, therefore, examined in great detail.
Painter (1943) is of the opinion that hardness of tissue as a cause of resistance is open to question, but that differences in phnt structure may be found to be genetically linked with resistance a nd may hence prove to be useful marks in the search for resistance. The toughness of the cuticle of the leaf-vein of cotton is perhaps a character which is not the primary cause of resistance, but only an indication of it.
Hairiness of the leaf-veins
The association between hairiness and jassid susceptibility has been studied by several workers. Roberts (1915) has stated that glabrous cotton plants suffered more from jassids in the Punjab than the hairy plants. Parnell (1926-27) says that both the density and length of hairs play some part in inducing resis~ tance in cotton to jassids in South Africa. Peat's work (1926-27) in Rhodesia corroborated the findings of Parnell. Jewett (1932), working in U.S.A., with several varieties of clover came to the conclusion that there was no association between hairiness and the amount of injury done by E. fabce Harris. Johnson and Hollowell (1935) have on the other hand reported that in soy beans the hairy plants are resistant to E. fabce Harris. So far as cotton is concerned, Afzal Husain (1937) was the first to throw doubt on the utility of haidnesc; as an indication of resistance and later Afzal Husain and Lal (1940) came to the conclusion that much reliance cannot be placed on leaf-hairiness as 'it character of jassid resistance. Sloan (1938), working in Queensland, says that there is closer relationship between length of hairs and resistance than between the density of hairs and resistance. He also found that, although all resistant plants were hairy, all hairy plants were not resistant. Parnell and MacDonald (1941-42) have shown that, in South Africa, all hairy cotton plants escape jassid attack.
Marriott (1943), working in Queensland, found some correlation between hairi· ness and resistance, but under certain conditions even the normally susceptible glabrous phnts withstood the attack. MacDonald, Ruston and King (1943) have stated that all previous experience at Barberton has indicated an extremely marked relationship between hairiness and jassid resistance in cotton. Painter (1943) in his review of insect resistance of plants in relation to insect physiology has stated that, in cotton, the effect of pubescence comes through oviposition reaction rather than food relationship.
86 COTTON JASSID IN THE PUNJAB
As regards the position of the leaf on the cotton plant, Peat (1926-27) found that leaves near the growing point were less hairy than the older leaves. One of us (Afzal, 1936) has, however, shown that hairiness increases from bottom to top, and therefore, any correlation between hairiness and jassid attack must be calculated after taking the position of the leaf into account. MacDonald, Ruston and King (1942-43) have corroborated the above findings of Afzal (1936). They found, for
both lamina and mid-rib, a steady increase in the density of hairs and reduction in length as the leaf-size decreased. The upper leaves are always smaller and carry denser and shorter hairs than the older and larger lea ves.
Previous workers have studied the hair density on the general surface of the leaf, but, as the jassid females lay eggs inside the vein, and, as has now also been proved, that the vein is the only focus of infection, the hairiness of the leaf-vein only was considered in the Present studies. It must, however, be mentioned that the hairiness of the leaf-vein, the hairiness of the general leaf surface and the stemtip hairiness are closely associated and the plant breeder will, normally, depend on the stem-tip hairiness for making his plant selections.
The method of work employed in the present studies was as under: -The leaves of a large number of young plants chosen at random from the
pure varieties and hybrid progenies were tagged with a dated label on the day of separation from the apical growing point. The age of the leaves was thus known. Thehairiness was determined from mature leaves of 22 days age.(Afzal, 1933) only. One cm. length of the three prominent leaf-veins from these leaves was taken from as near the pulvinus spot as possible and the average hair density and helir length were determined.
(i) Hair density The average number of hairs in one em. length of the leaf-vein of pure
varieties sown at the normal time was first determined in 1941. These data are
given in Table LV. TABLE LV
Average number of hairs on one em. length of leaf-vein.
Leaf position 289F/K.25 I 'Victory' 289F/43 L.S.S. 199F
I-~---- -- - -_ .. _------
15th 1.88 45.46 54.46 68.60 I 3.45 20th ]4-.20 11.60 131.15 ... 139.41 25th 11.64- 14.65 103.65 161.47 173.67 30th 16.10 I 15.65 169.19 138.99 190.84 35th
\
7.65 i 14.76 105.42 113.90 128.01 40th 24.65 i 34.98 107.15 134.19 111.44
I ----- I ---Field notes on
I
Very Susceptible Resistant Resistant yery
I resistance susceptible reSIstant
CHARACTERS OF THE LEAF-VEIN ASSOCIATED WITH RESISTANCE 87
The above data were analysed after transforming these to log (n + 1). The means of the transformed values as well as their antilogs are given in Table LVI.
TABLE LVI
Mean No. of hairs per em. length of leaf-vein.
199 F I L. S. S. 289F/4-3 1'Victory' 289Fj S.E. C.D. at K.25 :t: 5% ±
----- ---- --~-.- "-~.--.---.-
Mean of trans- I formed figures ... 2.1128 2.0692
1
2.0168 1.154-5 11.0539 0.0525 I 0.1544-
Antilogs I ... 129.6 1117 .3 \104.0 14.3 )11.3 .., ...
I
It is clear from Table LVI that the resistant varieties had a distinctly larger number of hairs on the leaf-veins as compared to the susceptible ones.
The average hair density on leaves of different positions is given below:-
TABLE LVII
Mean hair density on leaves of different positions.
J_~Oth I I
S. I 30th 25th 20th 35th 15th E. C. D. at
± 5% ± .. _. __ ... _._--- -_. __ .. _._.",,.-
Mean of I
trans-1.8231 11.7532 formed figures 1.8365 1.734-6 1.6673 1.274-0 0.0575 0.1696
Antilogs ... 173 .03 66.55 i56.65 54-.28 46.48 18.79 ... . ..
It will be seen from Table LVII that only the 15th leaf had a significantly lesser number of hairs than the other leaf positions which did not differ from one another significantly. This is contrary to the findings of one of us (Afzal, 1936) where it was shown that the number of hairs increased from the bottom of the plant to the top. No suitable explanation of this disparity can be offered a t this stage.
It has been shown above that, so far as pure varieties are concerned, the more hairy ones were found to be, in general, more resistant. This finding was checked up from records on hybrid progenies. Progenies No. 204- and 226 which have already been dealt with in connection with the toughness of the cuticle were examined. The plants of these progenies could be placed in three classes by visual examination, viz., very hairy, medium hairy and almost glabrous. The
hair density of the two extreme classes was examined in order to obviate the overlapping effect of the 'medium' class. At the end of the season these plants were
88 COTTON JASSID IN THE PUNJAB
classified by independent observers for susceptibility. These plants are arranged in a frequency Table as under :-
TABLE LVIII
Frequency distribution of hair density.
Class interval of hair Mean No. of hairs! N umber of plants .. _-----
No. per cm. per cm. Susceptible Resistant _---------
0-10 5 1
10.1-20 15 7
20.1-30 25 8
30.1-40 35 3
40.1-50 45 4
50.1-60 55 1
60.1-70 65 3 1
70.1-80 75 2
80.1-90 85
9{).1-100 95 2
100.1-110 105 2
110.1-120 115 2
12(H -130 125
130.1-140 135 3
Over 140 1 6
A study of Table LVIII reveals that, in general, there was very close association between hair density and susceptibility. The less hairy plants were generally found to be susceptible. There was only one exception where an intensely hairy plant was found to be susceptible. The occurrence of such plants, however, does not invalidate the general opinion expressed here that hairy plants are usually resistant. Sloan (1938). Afzal Husain and Lal (1940) and Marriott (1943) have also recorded a similar phenomenon.
CHARACTERS OF THE LEAF-VEIN ASSOCIATED WITH RESISTANCE 89
Disregarding the exceptional plant, the data in Table LVIII could be
worked out as follows :-
TABLE LlX
H air density in hybrid progenies.
I Class of plants Mean No. of hairs Standard deviation'
Susceptible 34.31 ± 19.427
Resistant 127.50 ± 18.314
Coefficient of variability
---~---.---
:f: 56.622
± 14.364
It will be seen from Table UX that the susceptible plants were distinctly less hairy than the resistant ones. It may also be noted that the resistant plants
had a much narrower range of variation than the susceptible ones. This point has an important bearing on selection of plants by the cotton breeder. He must select the very hairy plants and these plants will, in a large majority of cases, be resistant to jassids.
This work was repeated during the succeeding year when both the hairiness and the jassid population were determined. These data are given in Table LX.
As a result of four years' work on pure and hybrid strains, it can now be definitely stated that the selection by the cotton breeder of hairy plants will automatically bring in its train the character of jassid resistance. Afzal Husain and Lal (1940) have advocated a de novo examination of this problem, but it has been shown by us that hairiness and jassid resi<;tance usually go together.
It is, however, not suggested that hairiness is directly linked with jassid resistance. If hairiness as a physical character of the plant were inhibiting oviposition and were, thus, directly linked with resistance, then the artificial removal of the hair from the leaf-surface should render the plant susceptible. That this does not happen was shown by shaving the alternate leaves on four plants of 199F in 1943 at the time when the jassid attack was at its highest. The
90 COTTON JASSID IN THE PUNJAB
III ::-
.... 0 • ..0
~'" "l"tl C
'" 0 v -i-"/ .... 0 .... N
0 >. .... C N <II
1>0 0 ....
0 ... .... ...... N 0 . ..... .... ..... ..., ci '" 00 ..c .... ...,
"' c,; --- ------------ .... <II
<:u 0 * ..c .;::: ,..._ 00 .... -0
<:u en .... . .2 l;l,() ....l .... C ..: ci N :.a ~ > 0.. ~
II") ~ J>l ....
~ f-< ..0 ~
N ... N ..c 0 .,.
>. ?-. en II") .... ~ '" '-;' c;
..: <II
~E ....l .... OJ)
S ci .... ,_, ..... IV"> ,.., 0 N
.... $:! ,.., ...
X .9 z ..... 0 0
~ ...,
f:: <:l ... "' ;; ..: <:> ... C; II'! ....l N '" .... >-l 0.. ;:0 .... .... '" P< c '" .!. a. -< 0.. 0 ci .... "1 .... ('l .....
f--< '"t::l ... 0\ 0
.... . ~ II)
'" .0 <:l ... II " (> " * E ...... ..
0 .... 11") N .... ..... .... .... :::l '1::l 0\ C ;: ,..!, II) <:l 0 .... {',1 .... N .... .s '" \0
'" II)
<:u ...,
.E '" .~ ... '" .. (> .. "tl .<j 0 .... \0 .... ..... c
::r:: 'q ,.., "tl ci .... .... .... .... II) .... '" ....
.:g '" '" II) ...
0 :::l OJ)
'" <.c; .:. II)
..c b I
~ !i '" 0
C;; Z "':> '" .... 0 0 0 0 0 0 0 0 0 "'''' 0 ~ 0 c: .... N -of" \0 co 0 N V \0 0 N ..,. ._ c: . , . .... ..... '-;' .... '-;' ('l "/ "/ ..... _ .:. ,!; .:. , .:. .; VJ ..... r:! ,..., .... .... r:! .... ,...,
::C:~ ci 0 ci ci 0 ci ci 0 ci <0 ci N "1" 0.0 co 0 N .... \0 00 0 ~ Q .... .... ,..., ..... .... N
CHARACTERS OF THD LEAF-VEIN ASSOCIATED WITH RESISTANCE 91
number of nymphs and, the leaves of these plants.
therefore, indirectly the egg-laying, was studied on aU These figures are given in Table LXI.
TABLE LXI
Nymphal population on shaved and unshaved leaves (1943).
Type of leaf No. of leaves examined
Total nymphal population
Nymphal pOpulation per leaf
---------- -------
Shaved 902
Unshaved 914
376
364
0.42
0.40
This experiment was repeated In 1944 on the same variety and data are tabulated below:-
TABLE LXII Nymphal population on shaved and unshaved leaves (1944).
Unshaved leaves.. I Shaved leaves
Date of observation Nfl I No. of- N-i-I---I -NO~of--o. 0 eaves h o. 0 eaves h examined nlmp s examined I nymp s
. ound I found ------
9/8 92 20 88 23 11/8 84 45 82 44-13/8 88 57 87 62 15/8 76 63 72 53 18/8 74 56 80 76 20/8 51 56 52 47 22/8 46 45
I 41 36
24/8 42 i
41 46 36
Total '" 553 383 548 377 Nymphal population ~.--
per leaf '" '" 0.693 ... 0.688
From these experiments it is abundantly clear that shaving of hairs made no difference whatever in nymphal population. It may, thus, be stated that the physical presence of hairs on the leaf-vein does not induce resistance. It may, therefore, be concluded that hairiness a.nd resistance are only visible symptoms related to some unknown character of the plant, and, therefore all the three go together. It would be very interesting to find out this character, but efforts in this direction have so far proved in vain. From the cotton breeder's point of view, however, it is enough to know that hairy plants are resistant to jassids and it is, therefore, recommended that, in areas where jassids are a serious pest, the cotton breeder should select the hairy plants. Hairiness of the plant body is a very easily recognisable morphological character and the present work has been
92 COTTON JASSID IN THE PUNJAB
useful in setting all previous doubts regarding the utility of this character at rest, A further proof of this is found in the classification of the important
commercial varieties of cottons of the Punjab on the basis of jassid attack and hairiness. This classification based on the records taken at the Cotton Research Farm, Risalewala, is given in Table LXIII.
TABLE LXIII
Density of hairs in relation to jassid attack.
Order of j a ssid Class of attack
Variety Remarks hairiness
1937~~8 I 1939 --1---- ---
L.S.S. ... 5 4 I 2 4 I The density of hairs and 289FJ43 ... 4 2 , 2 4 ~everity of jassid attack 4F 3 3 I 2 3 lncreases progressively ...
I 289FJK.25 ... 7 1 1 1 from No.1 onwards. 38F ... 6 1 2
----, ------- _"_' -1-"-'---39 Mollisoni ... 1 ... I ... I 5 Jubilee , .. 2 ... 3 6
,
It will be seen from Table LXIII that all the important commercial varieties of cotton in the Punjab have shown a close association between hairiness and re<;istance to jassids.
(ii) Hair length The hair length was measured on leaves of 22 days age by means of a
scaleometer on the same veins where the hair density was measured. The figures given in Table LXIV are averages of 135 measurements.
TABLE LXIV
Comparative hair length (1/ roo cm.) in different varieties.
Leaf position i289F /K. 251 'Victory' __ . __ •. ___ . __ : _ .. _~ _____ . ___ • ___ r._._ . ______ • ___ _
15th I 8.50 20th Ii 10.40 25th 11.24 30th I 11.73 35th i 9.63
-Field~::S on 1\1 ~:~y resistance susceptible
9.50 11.17 11.20 ] 1.82
\
' 11.53 10.05
-------
I Susceptible
199F 289F/43 I, L.S.S. 'I '--9.68---1 - -~.4~--- :--9,-84--
13.64 i 12.77 16.24 12.80 I 11.84 l3.60 11.62 11.26 13.38 13.31 12.24 11.75 10.13 11.45 9.76
-------- -----_ ------Resistant \ Resistant Very
resistant
CHARACTERS OF THE LEAF-VEIN ASSOCIATED WITH RESISTANCE 93
The figures given in Table LXIV were analysed statistically and the result of the analysis of variance are given below :_
Variety
199F
289F/43
L. S. S.
'Victory'
289F/K.25
TABLE LXV
Mean hair length in varieties and leaf positions.
I Mean hair I Leaf i Mean hair I
length S. E. length S.E. (1/100 cm.) I position
(1/100 cm.) I I
I ----~---- -- --.----~.,
12.43 20th 12.84
11.86 25th 12.14
11.34 ± 0,412 30th 11.96 ± 0.451
10.88 35th 11.69
10.03 40th 10.06
15th 9.16
It will be seen from Table LXV th'lt the mean hair length varied signifip cantly in different varieties and with different leaf positions. The resistant varieties had longer hairs than the susceptible ones and the hair in the middle of the plant were longer than on the leaves at the top or the bottom.
An attempt was also made to find out the association, if any, between hair density and hair length. Since the records given in Table LV and Table LXIV were taken on the same leaves, the analysis of variance of the figures in these two Tables was worked out. The correlation coefficient3 betweeu length and density thus obtained are given below :-
Leaf position
Varieties
r = 0.6243 Non-significant
r=0.8835 Significant at 5% level
It will. thus, be seen that amongst the Punjab-American varieties grown at Lyallpur the hair density and hair length are highly correlated and that both these are in their own turn highly associated with jassid resistance.
It may now be mentioned at the end that, in order to be classified as resistant, a cotton plant should have 120 or more hair per cm. length of leaf. vein (cf. Table LX). A cotton breeder has, however, not got enough time at his disposal to actually count the number of hairs. For his purpose grade.:; of hairiness must be proposed so that he can at once mentally classify the plants
94 COTTON JASSID IN THE PUNJAB
into grades. It is well known that the hairiness of the leaf and the stem-tip are closely linked and it is, therefore, suggested that plants of grades 1 and 2
of the stem-tip hairiness as proposed by Hutchinson, Ramiah et al (1938)
should be normally classified as resistant to jassids and those in grades 3, 4 and 5 as susceptible. Efforts should, however, be made to select plants as near to grade 1 as possible. After selecting the hairy plants the cotton breeder may be quite satisfied that he has got jassid resistant material.
It may also be mentioned that Afzal Husain and Lal (1940) have felt that, in the past, resistant varieties of cotton have been produced by the "hit or miss" method and have advocated a detailed re-examination of the problem and the methods adopted for the production of such varieties. It must, however, be recorded that success in the production of varieties resistant to jassids has been phenomenal. The production of U 4 in South Africa saved the cotton industry of the dominion from extinction. After the first onslaught of jassid attack and the failure of 3F in the Punjab in 1913, a remarkably resistant variety (4F) was produced in the succeeding year and this variety has withstood several very severe jassid attacks successfully. Numerous other examples; such as L.S.S. and 289F/43 in the Punjab and Cambodia in Madras (Bharat), can be quoted. Such resistant varieties cover extensive areas in different parts of the
. world and even a very heavy artificial infestation has done remarkably little damage to SOme of them (Afzal, Rajaraman and Abbas, 1943; Ramiah, 1944-45). All these varieties are resistant to jassids because these are hairy varieties and all the efforts of the plant breeders have in the past been directed towards selecting hairy plants. The present studies have conclusively shown that the method of plant selection adopted by the breeders in the past was the right method.
CHAPTER XIII
SUMMARY
Empoasca devastans Distant is a very serious pest of American cotton in the Punjab, and with the increase in area under this cotton, measures to evade or control this pest have assumed great economic importance. The Indian Central Cotton Committee financed a scheme of research on this pest for eight years at Lyallpur, and the results of this scheme which have been set forth in detail in the foregoing pages are summarised below:-
The collection of Empaasca spp. at Lyallpur by means of a light trap showed that E. devastans was positively phototropic and that the females were attracted in a much larger number than the males. It is considered th"t this method of control could be exploited further.
Of the different species of Empoasca attacking the cotton plant in the Punjab, the following three new species have been found besides E. devastans :
(i) E. minor Pruthi (ii) E. kerri var. motti Pruthi
(iii) E. punjabensis Pruthi All these new species have been found to be of very minor importance,
and E. devastans still remains the real and important cotton jassid in the Punjab.
A new finding which is of great interest is that under conditions of heavy attack by E. devastans the resistant varieties may show the outward symptoms of attack, the crumpling and reddening of leaves, but the yield and fibre properties do not suffer. Thus the planting of resistant varieties is a sure guarantee against the ravages of this pest.
The alternative host plants of E. devastans have been studied in detail and it has been found that the following are important:-
(a) Hibiscus esculent us (b) AlthCEa rosea (c) Solanum melongena (d) Solanum tuberosum (e) Hibiscus mutabilis (j) Hibiscus tiliaceus (g) H elianthus annus (h) Datura fastuosa
The methods of studying the population of E. devastans have been standardized, and it can be said that in varietal test plots sweeping with hand-net is an easy and an effective method of estimating the comparative population on different varieties. In complex agronomic experiments involving spacing, time of sowing etc., the method of actually counting the nymphs is found to be the more reliable method.
Amongst the American varieties which are at present grown on a large scale in the Punjab,4F, L.S.S., 28()Fj43 and 199F are highly resistant, while
96 COTTON JASSID IN THE PUNJAB
289F 1K.25 and 'Victory' are very susceptible. The desi varieties of G. arboreum
are practically immune. The seasonal and annual variations in the population of the insect have
also been studied. It is found that in certain years the pest multiplies en'ormously and the infestation is very heavy. During such years the susceptible varieties suffer greatly. This is illustrated by the yield records of the B.C.G.A. Farm. Khanewal. where 289F/K.25 is extensively grown. During 1942, a jassidfree year, the average yield on 705 acres of this variety was 16.17 mds. per acre, while during 1944 a year in which the jassids were in greac abundance, the yield was reduced to 4.65 mds. per acre. The effect of jassid attack is mainly reflected in the reduced number of bolls per plant. The only major differenc;e between these two years was the virtual absence of jassids in 1942 and their great abundance during 1944.
The infestation starts in the end of June or the beginning of July i.e., six weeks after sowing, and reaches its peak in the latter half of August, after which the insect population steadily declines until it practically disappears by the beginning of November. High atmospheric humidity has been found to be the chief cause of the high population in years of severe infestation.
The insect appears to prefer mature. leaves of 35 to 45 days age for egg-laying. The very young and the very old leaves are not infested.
Changes in agronomic practices affect the population of E. devastans, the most important of them being delayed sowing and wide spacing. The populat~on increases steadily as the sowing time is delayed and the distance between the rows and the plants is increased. Heavy irrigations appear to be conducive to a higher jassid population, but since the Punjab farmer can apply an almost fixed quantity of water to his crop, this finding is only of an academic interest.
The nature of resistance has been investigated in great detail. Bionomic studies on this insect have shown that the resistance or susceptibility of a plant depends on the ability or otherwise of the insect to lay eggs in its leaf-veins. If the eggs are once laid the hatching of the same and the development of the nymphs are in no way affected even in the so-called Immune varieties.
Amongst the characters associated with resistance, hairiness of the leafvein is the most important. Hairy plants are resistant to this pest. The other characters so far studied. viz., the thickness of the cuticle, pH value of the cell sap. moisture content of the leaf-vein and toughness of the cuticle are either not so important or not easily determinable. From the plant breeder's point of view. therefore, the hairiness of the plant body is the only dependable and also an easily recognisable charactei' and it is suggested that, in places where jassids are a serious pest, only hairy varieties of cotton should be grown.
97
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ERRATA
Page 9 line 16 For Marshal read Marshall line 38 For phases read phase
" 10 line 4 For Actu I read Actual Footnote line 1 For jasids read jassids
line 2 For suring read during
" 28 line 1 For results read experiments 31·47 Folio headings For e. devastans read E. d.vastans
49 Fig.3 Folio heading For ccotton lead cotton
" 58 line 1 For Ord r read Order
" 61 line 17 For 2')( 3 read 2' x 3'
63 line 16 For 2'x 3 read 2'X3'
84 Hne 20 For jones read ones 91 Folio heading ForTHD read THE
" 92 line 1 For comma read fullstop after rest.
