5. VANATICN IN IJFE-TABLE CXAR4cI'EWS'MCS AKtG

axoRX5 OF mxmQQTEs SPLEM)ENS. UNDER

FEEDIN REG=

5.1. J n t m :

After the pime2rir-q work of Morris and Miller (1954) on the

spruce hxbonn, the life-tables have been recognized as useful tools

in the study of insect popllation dymnics. m e r , the mtructim

of life-tables has only recently been applied to mDsquitoes (Service

1971, Scutlwood & a. 1972, Rajagcpalan a. 1975, Reisen ti

MahmJod 1979, 1980; Reisen gt A. 1979, 1980, (lmwddisai gt a. 1983). ?here a m two basic types of life-tables m l y timespecific

vertical life-tables and age specific horizontal life-tables. Wdle

vertical lifetable is used to study the species having either

werla~ping generations or a m t i n u a s recruitment (Deevey 1947), the

age specific life-table is used to study the species with disnete

non-overlappirq generations and preserrts a useful tabular sum~sy of

mrtality and reproductive schedule. It msasures the fate of a real

cchort, such as a nrmber of individuals of a swle @ation. ?he

advantage of the laboratory analysis of life-tables of PreQtOrS of

mosquitoer; is that life-table dmmzkristics can be studied by

mniplatirq biological factors whi& are knaJn to influenz life

structure of an organisn. ccrrstruded umler insectary

dtiolls, with the different rate of raticnal f w , keep* the

other variables uxrstant, lifetable of a predator will w p m

species genetic potential under sucfi cwditims iud m y be used

study the effect of different fadDrs on the survivorship and

w i v e strategies. Ihe life-table of 2. stu3ied

earlier bed &in aqx3A.s of biological dmraCteristi~~

87

(Ch-disai & &. 1984). TIE life-table approach has been applied

in recent time to shdy the survivorship and reprabztive strategies

of colonized culich mosquitoes like daoestic &. a&i (mrel lo

& Hacker 1972) Q. guinauefascia~ (Walter & Hacker 1974) and Q.

tritaeniortmchq (&isen &. a. 1979). w e r , m l e t e

survivorship and fdty-fertility dxxiules have not been &ded

for the genus ~ ~ t e s . 'Ihe pupose of the s b d y %as to assess

the potential of focd limitation in aborts of T. wlendens,

specifically to detemine the effect of prey availability on fluviva1

of imnatures, adults and Etdult fexrdty.

5.2. Materials and Methods:

5.2.1. w: A wild type laboratory strain of _T. s~lenlens, bred f m third

and fauth instars collected fran field in 1977 was used

the shdy and was in generation FlE2 at the tine of experimentation.

5.2.2. &olwical methods:

A6 the rate of fed.r~~ durw the lamal stage has a direct

bearing on the lanature duration, inmatun? survival, rate of

prpation, adult aeqenx, sex d o , adult f d t y and aiult

survival, series of experiments were u d x b k e n to rear a z b r t s frcm

egg stage at different pley regimes (- Table 5.1 far different prey

ragimae) . In all, eleven prey regimes sucfi as first, second, third

ard faurth instam of &. a&i at nuhers 5, 20 and 40 per

prsdator w a x d e d for their effect m the life-table

dnracteristic of T. ~lme replicates were maintained for

each set of p b n t ( ~ 3 ) . Cchorts of 200 eggs obtained frcm the

pl& in ea& of eleven 45 X 40 X 5 an hays

88

f i l l e d w i t h 3 lit. tap water. T. mlendens larvae were fed by

pmvidtrg pray as per the prey regime on daily basis until the last

m d x x plpated. Old prey were w e d daily rurl replaced with

respective rnrmber (as per the prey regime) of fresh ones. Similarly,

water in the trays was changed daily to keep the quali ty of water

collatant thmqhat t h egeriment. Ihe n u of lanrae successfully

~ u p a t i r g each day were axlnted ard kept separately in 500 ml beakers

ccmtahhj tap water. Dates on which adults anerqed were noted.

Mdian plpation (P5,,) a d enk3.y- (E50) tims were calculated

by f i t t i r g regressh of the fom Probit (P) = a + b Inx, where P =

anrulative pmportion plpating o r emxgirq an each day (x)

transformed to probits. Ihe PS0 o r E50 values were then

c a l d a t e d by sa lv i rq the qua t ion for P = 50% ( k i s e n and Mahmood

1980). Fkqmrtion of e g hatch was calculated fm the nw$er of

f i r s t instars anergirq fnm 200 egs. Sex r a t i o of the emerging

adults was also detemuhd.

Females ard nrales emeqed f m each s e t of exper-ts were

released into 0.3 m3 ucuquito cages, where they were continuously

offered b y pad, glucose pad and wiposit ion t r ays w l t h water. As

we did not ge t the prcblem of bacterial and/or furqal contanination

of hcney @ in c u r insectary, honey pads were charged only o m in a

fortnight. Haever, glucose pads were changed on alternative days.

O v i p i t i o n containers were chanqed daily. Eggs were counted daily.

Each morning all dead adults were removed, separated by sex and

recorded.

5.2.3. Stat;ist-ical methods:

Adult l ife-table characteristics were estimated following the

methods of Reisen & A. (1979) and are Smmdt-iZed a s follows.

1. +specific survivorship, lx = Yx/Yo, hbere Yx = flre

~~ of males o r females alive on each day, x . By f i t t i n g a

89 -irn expression of the form log, lx = log,.a - x l q e s to

the -ific survivorship estimates, it was possible to define the

form of the 6uNiMlship m e statistically. If the regression

e f f i c i e n t , log, s, significantly differed fmn 0 wllen tested

by analysis of variance, survimrship was asmmd to be corrstant,

i.e., a Qpe 11 sunrivorship curve (Deevey 1947). A m i g n i f i c a n t

F rat io in the analysis of vari- d d indicate either a '&pi! I

or 111 a w i m m h i p a w e (tkevey 1947), on the

pint of inflecticm. Ihe back-trat?sformed regressicm coefficient

prwided an e s th te of ccrstant daily survivorship ( s ) urder

laboratary m n d i t i w . W

2. Pge-specific l i f e expectancy, ex = Tx/lx, where T~ = Xh, x=x

khfx=~ I j ( = (h + 1x+1)/2 & w = the day the last individual

died: i - e . , el = adult l i f e e q e 3 a - q a t anergence in days.

3. Ihe net rqmdwtive rate per cdzort, or the total m m k s of living

females prcdwx~ per faale psr generation, % = a$$*, rtue Xr 1

a = the mean pmporticm of faa les that survived fmn egg thrwgh adult

emergence, and % = Q, w h e r e ~ i s t h e m e a n n m h r o f larvae

(i.e., ha- eggs) pmduced per female per age interval, x, and

p = the proprticm of the offspring that were females. For c a l d a t i n g

the net reproductive rate, sex ratio was assume3 to k 1:l. The mean

pmportim of faa les that survived fmn egg through adult emerg-

for different prey rrgims are given in Table 5.1. W

4. Age of mean &rt reproduction in days, To = a xlp$R,,, Y = l

startirq a t x = 1, the day of adult emeqence.

5. Capacity for increase, rc = lni$pO.

6. The i m t a t - ~ w rate of increase i n females per f d e , rm, w a s

calaated using the Dobzhansky & d. (1964) d i f i c a t i o n of the

original Euler-btka equation solved by the Newton-Rephson i t e n i t i ~ n w

method, where 1 = a >: l,pp-m(X+D) and e is the base of natural

x: 1

90 1ogaritI-m ard D is the lergth of tim fma wipasition i n the present

generation to f i r s t mipasition in the offspring generation. In the

present d x i y , D was considered to be the mean median emeqerce the

for females plus the duration of the nullipamus period for that

cohort. Ran dxmat ions , it was f a d that f i r s t wipasiticm in mst

of the cahort coxmd by day 5. Man median emergence time for f d e s

is given in Table 5.1. 'Iherefore, values of D for different prey

r e g h bere arrived a t by totall* mean wdian meqence time for

fanale and nul l ipam~s period of 5 days.

7. Mean generatim time i n days, G, was then calculated by a f o d a ,

G = lrB,Jr,. Since this value includes D in its calculation, G was

a mre real is t ic esth te of t d frun mean wipasition in the present

generation to mean w i p i t i o n in the offspring generatim.

8. Irstantanecxls birth rate was calculated as b = ln(1 + p ) , where W

1/8 = Lp-rw(x+l) (Birch 1948). Instantanems death rate was 19

calculated as d = b - r,.

Qnprison amcng prey regimes were made with one-way analyses of

variance (AMJVA). ANOVA tables were carpleted by setting 95%

carpariscn intenmls by Wthod (Gabriel 1978) for means (for

details of the test see &ion 4.2.2) . ~npr i scP l anurg l i fe tab le

statistics werx made by correlation analysis fmn mean values for

each prey regime.

5.3. ReGUlt$:

5.3.1. &mml life-table ~ c t e r i s t i c s of T. s p l m as fundims

nf-:

Mean prcportion of eggs h a W mqd fmn 0.81 to 0.96. One way

analysis of v a r i m applied on the data &sid no significant

differexe i n the egg hakh a w q the egg batches (E4.05) ( W e

5.1). ?he different prey regimes treatments clearly had a significant

(Pc0.001) effect on the varicus larval life-table parameters of T.

swim. ?he survivorship of 2. solenders fmn first instar to

plpae was significantly (P<0.001) greater when reared u m k r the prey

regime of 40 seand instar, 20 thhd irstars a d 40 third instar per

predator per day when mnpared to other prey regimes (Table 5.1, Fig.

5.la). RLis trad in the survivorship of T. sulendens was also

noticed in the h t u r e aurvivorship frcm first instar to adult

anergenz (RO. 001) (Fig. 5. lc) . 'Ihe imMture survivorship frcm first

instar to adult was significantly correlated with male-fade ratio

(r = 0.55, R0.001). T. splerdens shantd significantly (P<0.001)

lwer survival between plpal stage arid adult meqence at 5 first

instar prey/predator/day regime. However, other prey regimes did mt

differ among -ves as far as survival of ~*lpa to adult is

omxmd (Table 5.1, Fig. 5.l.b). Mgliandevelcpmtal time f m $

to plpa (P50) was influe. by the prey wines significantly

(R0.001). Pihen 20 fourth instar of &. aeqypti was off&, time

taken by 50% of the predatDrs to read stage was only 11.38

days: ukmx~~, the prahtor uhen reared urder prey regime of 5 Secorri

instar prey/predator/day t a c k as lcq as 56 days to carplete 50%

plpaticn (Table 5.1) . Similarly, analysis of variance on dif faent prey regimes as treatment effects s h a d that there- a hiey

significant (R0.001) effect of prey regime on the madian eaergenoe

time fraa L1 to Adult ( E ~ ~ ) (Table 5.1). lhere was no adult

aoergenm when T. &emlens m s offered prey regime of 5 first instar

of &.wpmlator/day. T. -, when d under 20 b 40

first instar ard 5 seand instar prey/mtor/daY reg*, took

significantly (~co.001) (~ig. 5.ld) 1- to read e t

the when un3er all other p~ reg*. In case of

Table 5.1 nnrmture developmtal attributes of T. s11L-g as functions of prey size class (&. amti) and density. ii

p-

Attribut? @ Prey Prey instar density 1 2 3 4

- hpportion 5 0.9 (0.08) 0.84(0.09) 0.88(0.01) 0.9 (0.06) egg ha# 20 0.81(0.12) 0.96(0.01) O.gl(0.04) 0.89(0.05)

40 0.%7(0.12) 0.16(0.05) 0.83(0.06)

Total Survi-***5 0.00 O.Ol(0.009) 0.17(0.04) 0.19(0.03) vorship 20 0.04(0.01) 0.15(0.06) 0.47(0.02) 0.37(0.24) Ll to A(totdl)40 0.12(0.09) 0.35(0.05) 0.49(0.06)

Total Survi-***5 0.00 0.007(0.006) 0.08(0.02) o.l(o.02) v~rship 20 0.02(0.01) 0.08(0.05) 0.27(0.02) 0.2(0.13) Ll to A(male) 40 0.06(0.08) O.lg(0.03) 0.24(0.0)

Total Survi-***5 0.00 0.003(0.003) 0.09(0.02) 0.09(0.02) vorship 20 0.02(0.0) 0.07(0.006) 0.2 (0.0) O.li(O.11) L1-A(fde) 40 0.05(0.02) 0.16(0.02) 0.25(0.06)

# mean(SD), IF^; attributes unrM with asterisks denote significant d i f f m amq the treatments us& ANOVA. * 0.01 < P < 0.05; *** P < 0,001. @ L1 = M larml instar; P = m e ; PS0= "dim developwntaJ time f m L1 to P; A = adult: E50= mdian emergence the frcm Ll to A.

Cont.. .

-5J 95% capxiscn intervals by the T-method (Gabriel 1978) for the means. Warn kllrose intenrals do not overlap are siqnificmtly different.

-0.2 1 1 A B C D E P G H I J K

Prey regime (a)

80 1 I

-20 u A B C D E F G H I J K

94

other prey regimes such as 20, 40 d, third and fourth irstars of

&. ~ & ~ , median e m q m x time f m $ to adultwas in the

range of 16.03-27.45 days ard the diffemm? in this ranp was not

significant at the 5% exprimentwise error rate (Table 5.1, Fig.

5. ld) . 'Ihe pnportion of offsprirqs that were f d e differed

significantly (Pa. 05) amc~lg different treatmnb (Table 5.1) .

5.3.2. Adult life-table characteristics of T. s~lendens as fcolctions

of DW mimes:

The different prey regime treatments also had a significant

(RO.OO1) effect on the varicus adult life-table paamters of _T.

wlerdens (Table 5.2). Femle life e p d a q (el) of T. solexlens

varied amMg eleven prey regimes only at the significant level of P

0.05. Ihe m q e was 0 - 47.84 days (Table 5.2). Since border line

significance is not free fran doubts about the real significance in

the diffennce of female el, and the 95% oxprison intervals by

the T-method for the mans when plcrtted werlKped with each other

(Fig. 5.2b), it d d not be conclusively stated that fanales fmn

cahorts of l m e reared m%r different prey regimes differed in

their el significantly. Hence, it is inferred that there was no

significant effect of prey regimes on the el values of the female.

Howwer, the male life expechq at areqmx (el male) differed

significantly (R0.001) . The raqe was 0 - 50.23 days (Table 5.2). Males fmm larvae reared uorler prey regimes of 5 ard 20 first irstars

of &.mi &wed significantly la~er el than males from larvae

rear& h&her prey size ard densities at the 5% experhntal

error rats (Fig. 5.2a). Males f m ~~ reared I.u'&L- regimes

of 40 first -, 5, 20, 40 seand and third instars and 5 +@ 20

95

fourth instars per predator per day showed higher el and the

difference of el anqq them was not significant a t the 5%

experimentwise m r rate (Fig. 5.2a) . Ftqadbq f d e daily survivorship (6) , the results shaJed that

s was zero amcPlg females fmn larvae reared lrtder prey regimes of 5

f i r s t and semr~I instam of &. aeswti. On the other hand, females

reared fmn higher prqr size and density reginus showed significantly

(KO. 001) higber S (Table 5.2, Fig. 5.2d) . Same was also true in case

of male's daily survivorship (Table 5.2, Fig. 5 . 2 ~ ) .

Ihe net reprcdwtive rate (Ro) of T. mlendens a m q different

prey regimes were ccmpr&le. Highst net repnAudive rate i n l i v h

female per female per generation was cbtained in the 40 t h i d irstar

prey/p?xhtor/day regime (Table 5.2, Fig. 5.2e) . ?he secMd highest

was 20 fourth instar prey regime. Ihe lcxJest I$, was in the prey

regimes of 5 and 20 of f i r s t irrstar prey and 5 second instar prey.

UnapA&ly, &, was not significantly c o d a t e d with female l i f e

a p x b n q a t mkmgenm (r = 0.16, B0.05).

Age in days a t mean cahort repmdwtion (To) was significantly

(RO.OO1) lailer (- earliest in l i fe ) in f d e frna oohorts

reared under 5 ard 20 f i r s t irbstar prey r e g h ( m l e 5.2, Fig.

5.2f). Oxmrsdy, To was highest for the f d e s fmn higher prey

size-density regime. To was not significantly correlated with %

(r = 0.17, FM.05).

Ihe capacity for increase, rc, was higher a t higher W

sinxknsities (Table 5.2). It s W d be pointed cut that rc

utilized To in its c a l d a t i m , and thus was based

adult age.

rate of increase (r,) was f d to incnsase

significantly (R0.001) with inawse in the Prey s ize and sty

96

(Table 5.2, Fig. 5.29) . As qxcted, rm was positively correlated

with rc (r = 0.94, RO.OO1) . rm was also significantly comlated

with % (r = 0.76, RO.OO1).

'Ihe mean generatim time (G) of T. s~~lerdeq was significantly

(RO.OO1) higher at the high prey size and W i t y regimes (Table

5.2, Fig. 5.21) . As expected, G was significantly correlated with

To (r = 0.41, R0.05). As seen in rm, the ratio rm/b increased

significantly (RO.OO1) with increase in prey size and m&er (Fig.

5.2k). The instantaneaLs birth (b) anrl death (d) rates and the b/d

ratio were significantly (R0.001) higher at higher prey size and

density (Fig. 5.2i, 5.2j, 5.21 respctively) . As expct&, the birth

rate, b, and the &ath rate, d, estimated fmm the stableage

distribution &em fand to be clely correlated with r, (r = 0.74,

0.68 respectively, P<0.001) . L a e r birth and death rates aaxnpnied

by a l m rm a d fllggest a trend tckmrd grvater m a t i o n

stability (Reisen & a. 1979) . @ specific survivorship auves for males ard fanales ard

faxndity curves for females have been wicted gm@ically in Pig.

5.3. In general, female survivorship pattenr; a~proxhrdted

Slc&dkinis (1962) ~ ~ p e 11 m e with little iraease in mortality

during early age htauals (Fig. 5.3c,d) , while male curves exhibited

either 'Qpe I1 or I11 w e (Fig. 5.3a, b) . NLnaber of eggs laid was faxd to be high in the second week of

adult life anl egg lay* activity was obemd for 6-7 fran

adult energenz. In general, fenales - f m hi* prey

rarmbezcsize class laid more eggs than the f d e reared fmn

l w prey rkmity-size class regimes (Fig. 5.4a1b) .

Table Mult l i fe table cfiaracteristics of T. wlerdens as functions of prey size class &. pzamti) ard density. #

- 1.2-

- 0.9-

0.6 - 0 -

0.1-

-0.3 A B C D E F G H I J K A B C D E P G B I J K

Preyregime

800 (e)

600 -

8 400- IX

-2007 , I , , , , , , , , , A B C D E F G H I J K

prey regime

(4)

0.03

-0.01 A B C D E F G H I J K

-10 '1 A B C D E F G H J J K

Prey regime

-------- ----- -----

-40

-70 .

A B C D E F G H I J K

-0.3 A B C D E F G H I J K

Prey regime (k)

0 0.3i-lt 1 -0.3

A B C D E F G H I J K

prey regime Preyregime r) 12 No: ... gee,

C !

',$,i , i '," ,

. !'

Weeks

1Fis, Ap-qwific w i v o r s h i p in individuals per individual per

&y (lx) plotted a~ a ftmtion of Afie in W& for males (a,b) and

feuale8 (c,d) u n b different prey &ires. Each p i n t r e p m a t s

the mean of 3 replicates.

103

5.4. Q&&&&):

l fm =ins arrl rate of devdcpmt of T. m, s t d e d mdar different prey reghem hiwight the inportanz of

manipllating the prey availability po@atkn grarth of the

~~. 'Ihe lxeaent study m a d e i t e a s y t o a m p b t h e p r q i t a

rate of increase of T. @tim so as to prodwe the hs t

poseible quantificatim of m t i m Perpornarm. egg hatxhiq

rate (range 81%-96%) reported in the s b d y s q p s b an

effective fertilization and is i n agreement with Funnnizo and minick

(1978) uho reprted egg h a w rate of 7741% in T. w l m .

Harever, egg viability wa6 reporfed to be 57-1009 in other species of

the Tcocortrmrfrltes (Trimble 1979, Steffan & a. 1980). The

presglt experiment highlights the effect of fmd level m the lanml

an3 aihrlt life-table dnmcteristic of T. m. 'Ihe chuatim of

dsvelopmnt of immature6 of T. =1er&nfj at variars prey regimes ws

fastar than chemed by Paine (1934) uho reporfed mean dwelopmt

t h of 23 days far uell fed laxvae and 110 dap for starved lanme.

ChlY) (1968) reportsd imnature cbuatim of 39 days in T. m. Punaiu, arid Wlnidt (1978) reared T. at high prey Qrsity

a d abeanred the imaatme cbuatim of 21.5 days. I n t h e w

shdy, lredian aargenoe t i a a f m u L 1 t o A w a s i n t h e r a n g e o f l ~

Qys &ml fed l& to hig=tpreyregimen=Ftivel~. - o th r -88 shared vi& rarrge of imaatme -ti-. -,

it d bs, inferred that inwitme c)natim may ar

basad cn availability of the prey. -- ~~ be a f a e

Mluarcfng ttm kpmatura Qlratim in m-. By -yirg-

ppatian, T. laaintains the-feeding*-

mar rhich ~ p ~ t i c n mi ar*llt einm-=al M ~ Y

104

affected. It is also inferred fmP the present etudy that inmature

wuvival is prey size and density ckpmknt.

Ihe highest male and female life-expectancy a t mwpnm nas

edh ted to be 50.23 and 47.84 days -way. lhe data shar that

male -im l i t t l e laqer than fepale. cur irrsaPLMtion ~ h n t

has bd.cdted atleaat tm male to are female for effective

imdnntian. Heme, laqer male m i v a l is c x r d m d ixlaptive to

* ~ h . Ftcks & a. (1977) qmted that fenales of T. r.

mtilu fawived an average perid of 49 days and laid an average of

1 eSq/day. Purumizo and (1978) estimbd an a t l i f e s p n

of 28-35 days for T. m. HaRwr, a m x h m suzvival of 120

days was reported by Steffan d. (1980). In the present study, the

highest lnale and f d e daily survivorship was 0.98. The present

latoratary estimates of survivomhip and lcngwity vere pI-eslrmed to

depict the genetic p t m t h l i t y of this species. FWthenmre, the

ocntrihrtion of the individual a d e and f a a l e for the pcprlaticn

hcrease Lolld be dFrectly relatsd to l i f e e q e c b x y at emergence

ard lh Rrmber of f d e eggs pmked. Hi- % value of 518.33

was d h b d by feeding T. a m d with 40 third instar of &.

a ard ma f d to be times him than 16.3 reparted by

Qraarraaisai pb pl. (1984). Hrew, m (1955) wmtd f d e

f d t y of 400 eggs in labratmy dude3 of T. m. lhe

present stuQ F r d i r a t e s t h a t t h e w i p o s i t i a n p x i ~ ~ u p ~ M

d a p at prey -ity regime. Bh Steffan & a. (1980) reported a hic& wigadtim period of 8595 days. Zhis is mch lcrqer than the

27 dmp m p r b d for T. - (R & M c k 1978).

Ccqamtiwly, r,,, of 0.14 W e w m e* usn n s a n d ~ ~ ~ r e g i m e o f 4 0 t h F r d ~ o f & .

-,*. Higher valw of r, g e r n l y -b

105

to be an evolutimary adaptaticn to existing in or colonizing

variable ~lvimrments (Hairstcn gf; gL. 1970, Pianka, 1972). Heme,

w i t h M v e l y high potential value of r,, T. wculd be

able to exploit favorable 4- mu3I as the availability of prey

in large n m b r ani rapidly irmmae its pcpllaticn size. HaJever,

the r@ ani b/d ratioe, an Mkatim of weal wlcmizirq

ability (?lac Arthur & W i h 1967): hem relatively less. Thus, this

species W d be cons^ "P stmixgist, but relatively poor

wlonizer. Another adaptive dmmcbr fami in this species is

elcrqating G. 'Iherefm, higher g ard 5 related to high focd

level as tell as laqer d t lifetime give hcpe for exploibticn of

the species a g a h t ccntaiw hregLirq mr;qUitoes arfi as &.

aewpti. Pbod limitaticn during the imnature stage w i l l lead to

mdwticn in rutritiw reserve for egg mturaticn in the ovary,

rwsultirq in fcmr eggs laid by mu3I f d e s . Ihe pmsent Sturiy

Wotes that food limitaticn MIEXES an Organism in twoways

sxh as &cmmd survivo2ship and rdwd f d t y . anrS the

f d t y of tha arSrlt is determined by late of f e d b g ard food

a s s ~ t i m k i n g early l i f e pericd.