, I ,/ Entomology

I BIOLOGY OF RACHNESSA NICOBARICA (REDTENBACHER), A NEW GRUB SPECIES ATTACKING SUGARCANE IN

i i $ 1 ,

I LAMPUNG, INDONESIA

Sunaryo, K. Widyatmoko and U. Harsanto

search Division, PT Gunung Madu Plantations Bandar Indonesia

ABSTRACT

A new white grub of sugarcane, Pachnessa nicobarica (Redtenbachor) was re- corded in Gunung Madu, Lampung, Sumatra, Indonesia in 1985. This species has never been reported before in Indonesia. Observations on its biology were made in 'the laboratory and -in the field. Male and female adults can be distinguished

I readily, viz, the male's elytra are dull and dusty-like whereas the female's are glossy. The adults fly only above the infested field. Under laboratory condition and without food the females could survive for 25 days and each female averagely lays 28 eggs. The potential fecundity is 32. The generation time in the field is one year, the adult lays eggslin June, grub stage develops from July to March, pupal stage in April and adult in May. Observed egg population density is 2.5/m2 and the estimated potential density is 17.7/m2.

Key words: White grub, life cyole. 1 * I

INTRODUCTION 8 J '

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The whitelgrub pest of sugarcane has been very long acquainted in Indonesia, especiallyiin the island of! Java. Many grub species have been reported like Phyllophaga 'helleri (Brsk.); Eepidiota stigma F., Leucopfiolis rorida F. and Apogonia destructor Bos, (Kalshoven3, Wirioatmodjog). Among these L. stigma andL. rorida are still the in East Java and South Kalimantan (Pramono4).

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A new 'species is now reported at Gunung Madu sugarcane plantation in Lampung Province in the south of the island of Sumatra. .Having different characteristics from the familiar spedeb, it caused damage first in 1985: The damage has increased steadily, from only 50 ha in 1985 to approx. 500 ha at present. Symptoms of damage on canes are visible from November. The leavesiurn yellow and the plants generally grow weakly and stunted. Root hairs and portions of root tips are eaten up by the grub, but the underground portion of stalk and the old primary root are normally untouched. Although the distribution and the damage vary in the plantation, this new species is now a potentially important pest at Gunung Madu and deserves an extensive study.

ENTOMOLOGY

Specimens of adult beetles were sent to the Commonwealth Institute of, Entomol- ogy, UK, where it was identified as Pachnessa nicobarica '(Redtenbacher) (Scarabaeidae: Melolonthinae): The authors so far could not find any report mentioning the pest status of this species in Indonesia nor elsewhere. However, Brenskel in 1894 included a very brief description of a genus Pachnessa in his report on his expedition to Sumatra.

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The following report presents the'early results of study on the biology of P. nicobarica. The study was carried out both in the field and laboratory.

EXPERIMENTAL PROCEDURES ' > % *

1) Field observations , / )

Flighb of adult beetles was obServed in the evening just before dark. Flying and mating behavior were recorded. Vegetation in the infested field and its surround- ings wete scanned for the presence of adults early in the evening and in the morning. , ,

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Short ifiterval'(week1y) surveys were used to study the lifqcycle of beetles in one field (3 ha), hoping that even a shorts duration ohange 'could be monitored, These surveys were conducted by making 50 x 50,cm with 90 cm depthLpits. Six pits were dug for each observation, three in between Observations were carried out for 19 month period.

2) Laboratory observation

The flying adults, preparing for evening, and the catches ,were used for slaboratory 'investigation. In,,this case mating 05 adults was induced in the laboratory and then each mated<female was reared through its lifetime, in 6k7 cm container,filled with 4 cm of soil. Observa- tions were madesdaily and the number of eggs laid recorded. . .ir I

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The eggs were reared in other but similar containers to hatching time. Newly hatched grubs were fedawith rice sprouts and only after one month the grubs were fed with 12-3 week old sugarcane seedlings. ,The width of head capsule was taken once a week. Molting was noted as,when remnants of skin (ex

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Additionally, full grown grubs were collected from the fi laboratory to study the~biming of prepupation: pupation and adult 10ngevity~'~ r y .

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RESULTS

The adults are of medium size, body length is 11-16 mm, and body width is 6-9 mm. Pronotum and elytra are brown to black in color. Male and female adults can be distinguished readily, viz, the male's elytra are dull and dusty-like whereas the female's are glossy (Figure 1).

FIGURE 1. Male (left) and female right adult of P. nicobarica.

Additionally, the males have a slim body, the second to fourth tarsi of the fore and middle legs are thickened. Ventrally, the sternite looks semi-transparent, and there is a dark vertical line along the pygidium. The females have a larger size body, particularly so of the abdomdn; all the tarsi are slim, and the dark image on the pygidium is wider.

Newly emerged adults remain in the soil to complete the formation of gonads (David and Ananthanarayana2). The male adults stay in the soil for 16.7 + 3.4 days while the females stay for 23.2 + 5.8 days. Adult beetles will stay longer in the soil when soil moisture drops below 10%.

Most adults start flying just before 18:00 hrs at dusk. The flying activity gradually decreases until 21:OO hrs. The activity only takes place in the vicinity of the infested fields, at about 1 m either above the cane foliage or above ground level when the canes have been harvested. No aults have been observed to fly toward the trees or other vegetation around the cane fields.

ENTOMOLOGY

Adults did not show any feeding activity in the field. Similarly most of the adults reared in the laboratory (70% of 50 samples) did not eat during rearing period. However, some feeding test in the laboratory indicated that adults could eat various. types of leaves but in negligible quantity.

Catches of adults indicated that male far outnumbered females. Two to nine males were caught in proportion to one female. This is not the real male to female ratio, because detailed observation revealed that the males fly more than once while the females fly only once. A total of 150 males caught in the field were marked and immediately released back to the field. Out of this number, some 66 were caught for the second time mostly in the following day. The same treatment was applied to 120 females but only one female was recovered for the second time. On the other hand, rearing of full grown grubs and pupae collected from the field have produced 28 males and 21 females.

Mating activity starts with the flight of a female which is tailed by a number of males. Copulation takes place when the female lands on the ground. Copulation extends from 15 to 45 sec. After mating the female flys again for a few meters away and then it penetrates the ground on the infested field. The female starts laying eggs 2-6 days after mating. In the field, the female lays eggs 5-80 cm deep in the soil, averaging 68 cm. A total of 40 females reared without food in the laboratory could survive for 25.2 +. 7.8 days and lay 28.3 +. 11.3 eggs. If the eggs remaining in the female's abdomen are taken into account, the total eggs produced or the potential fecundity of a female is 32.2 rt 8.8 eggs.

The potential fecundity has a correlation with the female body length and follows an equation, Y = 54.0015 X - 40.594. The coefficient of correlation, r = 0.65, is significant at 1% level.

Eggs

The eggs are milky white in color, oval, have very thin chorion and could be damaged easily during rearing (Figure 2).

Initially the egg size is 1.6 mm long and 1.2 mm thgck. Fertile eggs will swell up to 5 days to 2.0 mm long and 1.5 mm thick. The egg stage lasts for 17.0 rt 2.3 days.

Larva (grub)

The C-shaped body is yellowish white in color. The head is yellow with strong mandibles. The spiraculum is not protruding.

A diagnostic characteristic of the grub is the shape and the pattern of the anal hairs. These hairs split into two lines toward the anal slit. Each line consisted of about seven bristles (Figure 3).

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FIGURE 2. Eggs of P. nicobarica.

Observation on the molting process in the laboratory perhaps did not give a real picture. The larvae could only survive under laboratory rearingfor 80-120 days, and within this period molting took place four times. The young larvae molted for about every 30 days and each time the head capsule width increased by 0.25 - 0.50 mm. The longest surviving larvae under rearing condition had less than 2.5 mm head capsule width. The frequent molting and the short survival of larvae in the laboratory (compared to the estimated 9 month larval stage in the field as d9scribed later) is probably because they were under stress due to frequent handling for measurement of their head capsule. According to Richard and Daviess, shortage of food will also increase molting frequency.

At the same time 49 last instar grubs collected from the field were reared and they survived to the adult stage. The prepupal stage was characterized by the inactivity of the grubs and then they ceased feeding. The last instar grubs about to prepupate have 4.7 + 0.3 mm head capsule width. The intestinal content, which previously could be seen from the transparent ventral side was later masked by the color change to yellow, body length shrank and stiffened to form some protective cell in the soil. The prepupal stage lasts 22.9 -c 3.7 days for males and 33.6 + 4.0 for females.

The pupa develops in an earthen cell . The pupa is white in color and has a very thin skin, exarate type and is prone to external disturbance.

ENTOMOLOGY

I FIGURE 3. Anal hairs pattern of larva of P. nicobarica.

I Three days before adult emerges the pupa color turns brownish. Pupal stage lasts for 16.3 * 2.1 days for male and 18.3 * 2.5 for females.

I Field population

I Population density of P. nicobarica in different stages of development in the field from April 1989 to October 1990 was shown in Figure 4 together with the growth phase of sugarcane.

Population counts of all the stages as found in the field from time to time are presented in Table 1. In the course of the survey the grub stages were grouped into three by its head capsule width, as follows: 1.0 - 2.5 mm, 2.6 - 4.0 mm and larger than 4.0 mm for early, medium and late instar grubs respectively.

The early instar grubs were mostly found in July to September, the medium ones in October to December, and the active late instar grubs were mostly found from January to March. Estimated duration of grub stage is about 9 months. The peak population for prepupae and pupae was recorded in April. In May adults were found in the ground and June was the time when the egg population is at its maximum.

There is a questionable feature of the data as the number of eggs was lower than the number of early instar grubs. Probably this was caused by the delicate nature of the eggs and also due to the simple method of observation applied in the

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SUNARY0,JZ WIDYATMOKO AND U. HARSANTO

survey which was not very thorough. However, the peak population of egg stage was still detectqble and the complete generation is cldied to one year. The first peak of egg population was 1.0/m2 observed in June ahd the second peak was 2.5/m2 observed in June of the following year. ' 1

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FIGURE 4. Field population density of Pachnessa nicobarica, April 1989 to October 1990.

SUNARYO, Id WIDYATMOKO AND U. HARSANTO

e infested field and this may lead to relatively slow dispersal from one field to another. Novertheless, disturbance on the habitat may cause a further dispersal. Harvesting activity at the time of flying period, or land preparation done at night, would be among such disturbances. Lights of vehicles or agricultural tractors might cause the adults to disperse'more widely:.

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Because female adults mostly fly only once (whereas the males, more than once), trapping or catching the females during flying may be worth trying as a control measure as the flying females may have not laid eggs yet. Another worker working on different species (Samoedi6) doubted the worthiness of adult trapping

assumption that the flying females may have ldd

The higher-than-normal frequency of molting of grub may be due to the stress and shortage of food in the artificial rearing conditions. This is in accordance with the findings of Davies and Richard2 working on Coleoptera and Wirioatmodjol0 working on Phragmataecia castaneae (Lepidoptera). Wilson8 stated that grub normally molts three times.

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The egg population density as given in the Appendix 1 could be used for computing the mean of population increase. Southwood7 used rc for the parameter of capacity for increase. This rc is the log e RolTd where RO is the net reproductive rate or the population of second generation divided by the population of first generation, and ~ c ' i s the generation time.

To compute the capacity for increase of the eggs of P. nicobarica in the field, it is found that RO = 2.38,iTc = 12 (months), therefore rc =0.0723. The actual monthly rate of increase is obtained by the antilog e rc =1.0750. This parameter is applicable in the field with all possible factors influencing the population.

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Another'approach is the computation of the potential rate of increase (rp), which ignores factors causing mortality, where rp = log e Rm/Tc. Rm is the mean maximum fecundi-'ty lx fraction of female in its population. In this case, Rm = 39.6 x 0.43 = 17.03, therefore the potential rate of increase or rp = 0.2362, and the potential finite monthly rate of increase is obtained from the antilog e rp = 1.2664. This value is comparable with that for Lachnosterna helleri Brenske (Southwood7), which had antilog e rp = 1.2986, when generation times are counted in months.

The difference between antilog e rc and antilog e rp shows theoretically the influence of factors causing mortality. The level of egg population of the second generation observed was 2.5/m2 but is theoretically 17.7/m2. Therefore, the actual

ENTOMOLOGY

population density is only 14% from its potential. If factors causing mortality are constant the egg population in the subsequent generation can be estimated.

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ACKNOWLEDGMENTS / * .

The authors are grateful to the managemknt of PT Gunung ~ a d u Plantations for the support given during the execution of the trails and in the preparation,of the report, as well as for the permission for publication.

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g , ' r REFERENCES

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1. Brenske, E. (1894). Zur kenntniss der Melolonthidep Sumatra's. Entomologische Zeitung. Herausgegeben von dem Entomologischen Vereine, Stettin. p. 275 - 280.

2. David, H. and Ananthanarayana, K. (1989). White grubs. in Sugar cane Entomology in India. (H. David et al. eds.), Sugarcane Breeding Institute, Coimbatore, India. p. 193-208. ., ,

3. Kalshoven, L. G. E. (1981). Bests*of crops in Indonesia (Revised and translated by P.A. Van Der Laan). PT Ichtiar Baru - Van Hoeve, Jakarta. 701 pp. ;

4. Pramono, D., Soeharto, D., Soewarno, Wiriatmodjo, B. (1988). Permasalahan hama tebu di lahan kering, dan , usaha pengendalianya. Seminar Budidaya Lahan Kering. P3GI Pasuruan., 14 pp. ;

5. Richard, O,,W. and Davies, R.G. (1977). Imm's general, textbook of entomology. Vol 1, Chapman and Hall, London. 395 pp., ,,

6. Samoedi, D. (1988). Uret hama potensial pertanaman tebu di lahan kering. Seminar Budidaya Tebu Lahan Kering. P3GI. Pasuruan. p. 199-207.

7. Southwood, T.R.E. (1969). Population studies of insects attacking sugar cane. In: Pests of Sugar Cane (J.R., Williams et al: eds.).<Elsevier, Amsterdam. p. 427455. % a r i

8. Wilson, G. (1969). White grubs as,pests of sugar cane. In: Pest of sugar cane (J.R. Williams et al. eds.). Elsevier, Amsterdam. p. 237-258.

9. Wirioatmodjo, )B, (1977). Himpunan diktat k~rsus~tanatnan. BP3G. Pasuruan. p. 199-204. (in Indonesian). <!r;l I > i * t i , 1 I ,

10. Wirioatmodyo, B. (1980). Biology of Phragmataecia, c~qtaneae Hubner, ,the giant borer of Sumatra, Indonesia. Proc. ISSCT 17: 1652-1656,

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BIOLOGIE DE'PACHNESSA NICOBARICA (REDTENBACHER), UNE NOUVELLE ESPECIE DE VER BLANCE RAVAGEUR DE

LA CANNE A SUCRE A LAMPUNG, INDONESIE

Sunaryo,,IC'Widyatmoko et U. Harsanto

Division des Recherches, Plantations de PT Gunung Madu Bandar Lampung 35226, Indontsie

RESUME

Un nouveau ver blanc sur canne h sucre, Pachnessa nicobarica (Redtenbacher) a CtC signal6 au Gunung Madu h Lampung, Sumatra, IndonCsie, en 1985. Auparavant, cette espCcie n'avait jamais CtC signalee en IndonCsie. Des obsefiations sur sa biologie ont CtC effectuees au laboratoire et au champ. On peut facilement distinguer les adultes'mtiles des femelles: les Blytres du mile sont ternes et comme poudreux tandis que ceux de la,femelle sont vernissks. Les adulltes volent uniquement au dessus 'des champs infest&. Dans les conditions du laboratiore et sans nourriture, la femelle pout survivre pendant 25 jours et pond en moyenne 28 oeufs, La fCconditC potentielle est de.32'oeufs. Au champ on observe une gentration par an; l'andulte pond en juin, les larves~se dCveloppement de juillet 6 mars, la nyrnphe en avril et l'adulte Cclot en mai. L;a densit6 des population d'oeufs observeks est de 2.5/m2 tandis que la densit6 potentielle estimCe est de 17.7/m2.

Mots clefs: Ver blanc, Pachnessa nicobarica, cycle biologique, canne h sucre.

I ENTOMOLOGY

BIOLOGIA DE PACHNESSA NICOBARICA, UNA NUEVA ESPECIE DE GUSANO QUE ATACA LA CANA DE AZUCAR EN

a /r , , ILAMPUNG, INDONESIA ,

Sunaryo, K. Widyatmoko y U. Harsanto

Research Division, PT Gunung Madu Plantations Bandar Lampung 35226, Indonesia

RESUMEN

Se ,registrb la ;presencia,.de un nuevo gusano blanco, $Pachhessa nicobarica (Redtenbacher) en Gunung Madu, Lampung,, Sumatra, Indonesia en 1985. Esta especie no se habia reportado antes en Indonesia. Las observaciones de subiologia se hiceron en el campo y,enel laboratirior Los adultosmacbo y hembra distinguirse rfipidamente asi: 10s Blitros debmacbo son opaco-oscuros como empolvados y 10s de la hembra son brillantes. Los adultos s610 vuelan pos encima de 10s campos infestados. En las-condiciones de laboratiorio y sin alimento, las,hembras pueden sobrevivir durante. 25 dias y ,oada hembra ,pone un promedio , de2 28 .huevos., La fecundidad potencial es de 32, El tiempo de la generaci6n en el campo es de un aiio. El adulto pone huevos en junio,,el estado larval, se,desarrolla de jvlio a marzo, el estado de pupa en abri1,y el adulto en mayo. La densidad obseryada de la poblaci6n de huevos es de 2.5/m2 y el estimati~o de la den~idad~potencial es de 17.7/m2.

Palabras claves: Gusano~blahco, ciclo de yida. a , b , . & I 1

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