J. Bioi. Control. 13: 25-31. 1999

Fertility table of an exotic parasitoid, remus Nixon (: Scelionidae) on Spodoptera litura (Fabricius)

CHANDISH R. BALLAL and S. RAMANI Project Directorate of Biological Control P. B. No. 2491, H. A. Farm Post, Bellary Road Hebbal, Bangalore 560024, Karnataka, India

ABSTRA CT: Fecundity studies on Telenomus remus, an exotic parasitoid of Spodoptera litura (Fabricius) indicated that in individual rearing, net reproductive rate was higher (120.53) and the population increased with an infinitesimal rate of 0.399 and a finite rate of 1.491. In group rearing, the corresponding figures were lower, being 65.03, 0.348 and 1.416, respectively_ There was a preponderance of females in the individual rearing method, while a balanced sex ratio was obtained in group rearing.

KEY WORDS: Fertility table, rearing, Spodoptera litura, Telenomus remus

Spodoptera litura (Fabricius) cabbage (Krishnamoorthy and Mani, (Lepidoptera: Noctuidae) is an important 1985). The release of T. remus in the field polyphagous pest infesting 120 host plants has enhanced the biological control of and is a serious pest on cole crops, tobacco, Spodoptera species in Barbados (Alam, groundnut, taro and castor (Singh and 1974), India (Patel et ai., 1979) and Jalali, 1997). TelellOmus remus Nixon Venezuela (Hernandez et ai., 1989). (Hymenoptera: Scelionidae) was recorded The construction of fertility tables to as an important parasitoid of S. litura in calculate certain vital statistics is an colocasia plantations in Western Samoa important component in the basic (Braune, 1982). This exotic parasitoid was understanding of the population dynamics introduced into India as one of the of a species (Southwood, 1978). The candidates for the biological control of objective of our present study was to Spodoptera litura (Fabricius). Field cage investigate variations in the fertility table studies in Karnataka revealed that T. remus of T. remus on S. litura when reared is effective in parasitising S. litura infesting individually or in groups. BALLAL and RAMANI

I and the number of female offspring MATERIALS AND METHODS x produced per female at age interval x as Telenomus remus adults and S. litura m . Utilising these, the following fertility x eggs .were 0btained from the cultures· table parameters were calculated. maintained at the Mass Production

Laboratory of Project Directorate of Net reproductive rate (R D) = LIx m x Biological Control, Bangalore, India. Approximate duration _ LxI x m x Adults of T. remus were allowed to mate of a generation (T) R and after a pre-oviposition period of 24 o

hours, ten pairs were kept individually in Approximate intrinsic _ log e R 0 15 x 2.5 cm glass vials with one pair in rate of increase (rc ) T c each vial (individual rearing or IR). Ten Precise intrinsic rate = e-r xl m =1 more sets were set up with ten pairs in each m x x of increase (r ) vial (group rearing or GR). Two cotton . m

swabs (one saturated with 50 % honey_ Net generation time (T) _ log e R 0 solution and another with water) were r m stuck to the inner wall of each vial. Finite rate of increase (A) anti log r Spodoptera litura eggs (0-24 h old) at the e m rate of 100 eggs per day per female were

exposed to the parasitoids in both IR and Weekly multiplication = (re m r GR niethods. The exposed eggs were of the popUlation (rw ) removed after every 24-hour period and a Hypothetical F2 females = (Rf set of fresh eggs was exposed. The o exposures were continued tiJI female mortality and longevity was noted. The RESULTS AND DISCUSSION adults emerging from each exposure were allowed to die, sexed and counted, and thus Figures 1 and 2 depict the age specific the fecundity (in terms of progeny survival and fecundity of T. remus in the. produced) was recorded. The experiment two methods of rearing. In IR, female was conducted at 26 ± 2 DC and per cent progeny production was observed to be relative humidity of 65 + 2. The fertility intensive for the first two days after the pre­ table statistics was calculated using the oviposition period, beyond which it methods followed by Andrewartha and reduced drastieally (Fig. 1). Hernandez and B:irch (1954) and was based on the Diaz (995) also reported that oviposition production of female progeny only. by T. remus on Spodoptera Jrugiperda (Smith) was greatest on the first and second The age specific survival (l ) and age days of the oviposition period. In the case specific fecundity (m) at each pivotal age of GR, female progeny production was high x was worked out for entire reproductive only in the first exposure (Fig. 2), afie~ period. The numb~r of individuals alive at which there was a sudden decline in age x as the fraction of 1 was recorded as progeny production.

26 Fertility table ofT rt'tIIllJ

.------l

69.5

59.5

E 49.5 ._._\_._._. >- o B ::::.. .t: F. -g 39.5 ~ l-O-~XI 1'" 0.6 =u=> -'-J. 1., 29.5 i ~ '"Q) 0> OA < 19.5 Jf

9.5 0.2

-0.5 ~ 0 12 13 14 15 16 17 18 19 20 AvOCal age (x)

Ag.1 Age specific lurvlval end fecundity 0' Te/enomuaremua In Individual rearing

----_._. ~---.-~------.-- ---" ~------

69.5

59.5 9 I" 49.5 I . E 0.8 ~ -;;; '0 . 0 ~ ~ 29.5 0 a. .,~ .,'" Q) -.-/x Q) 0.4 g Ol «'" 19.5 «

\ 0" 9.5 . .-.~.

·0.5 0 12 13 14 15 16 17 18 19 Pivotal age (x)

Fig. 2 Age specific survival and fecundity of Telef/omusremus In group rearing

27 tD ~ >-t:"" i ::t1 > T. a: Table 1. Comparison between fertility table parameters of remus in individual rearing (IR) and group rearing > (GR) ~

Method of Mean Sex Weekly Hypoth- rearing longevity Ratio multiplica- etical R Tc fc r T ').. (days) 0 m tion F2famales (d') (~) (d': ~) rate p IR 7.25 8.0 120.53 12.78 0.375 0.399 12.0 1.491 1:2.9 16.31 14527.48

t-..) co GR 5.20 6.5 65.03 12.12 0.344 0.348 12.0 1.416 1: 1.7 11.64 4228.90 Fertility table ofT. remus

The first mortality in the cohort pentatomid silkworm predator; occurred on the fifth day from emergence Canthecona furcellata Wolff.), r m was in IR and on the third day in GR. In JR, the recorded to be 0.275 (Singh et al., 1995) number of female progeny per female and in the case of Trissolcus sp., it varied ranged from 0 to 59.5 in the different from 0.1665 to 0.2775 depending on the exposures. The mean total progeny host species parasitised (Senrayan et ai., production was 168.2 and sex ratio (a: ~) 1988). The fertility of T. podisi also varied was 1 :2.9. The corresponding figures from 76.1 to 211 depending on the host recorded in GR were Oto 60.77,143.1 and species provided. (Pacheco and Ferreira, 1: 1.7, respectively. 1998).

The longevity ofT. remus adult females Ro and rm are generally lower in less was slightly more in the case of IR (8 days) fecund species, thus providing an index to in comparison to the adult females in GR parasitoid fitness. In this experiment, the

(6.5 days) (Table 1). Similarly, male same parasitoid showed different Rando r m longevity was also higher in the case of IR values, in the two different types of (7.25 days) in comparison to GR(5.2 days). exposure (Ro being 120.53 and 65.03 and

Schwartz and Gerling (1974) observed that r m 0.375 and 0.348, in IR and GR, T. remus could Ii ve longer when mass respectively). This indicates that the reared in comparison to solitary individuals. method of rearing causes variation in the This is contrary to the observations reproductive rates. recorded in the present study. This may be

because the adults in the experiment Table 1 shows that T cern,r ,r and A were conducted by Schwartz and Gerling (1974) all slightly more in the case of JR. The mean

length of generation (T ) was 12.8 days and were not provided with host eggs for C parasitisation. while in the present study 12.12 days in IR and GR, respectively, host eggs were continuously provided. which approximated the true generation time of 12 days in both. During this time,

The intrinsic rate of increase (rrn ) has the parasitoid could multiply 120.53 times been useful as predictive and comparative in IR and 65.03 times in GR. measures of population growth potential. Fecundity of scelionid parasitoids generally Earlier studies have indicated that the vary from 30-85 eggs (Singh et ai., 1995). age of the parasitoid and that of the host The actual number of eggs laid depend determined the oviposition capacity upon factors like temperature, stage of and sex ratio of the progeny of T. remus host, functional and numerical response and (Hernandez and Diaz, 1995; 1996). In the nutrition during larval development. present investigation, it was observed that Studies have indicated that the fertility of the method of rearing could influence the parasitoids could vary based on the type sex ratio and the reproductive rate. The sex of host eggs provided. In Psix striaticeps ratio was more female biased in the case of Dodd (a scelion id paras itoid of the IR, with the number of female progeny

29 BALLAL and RAMANI

being twice the number of male progeny. Mr. Hari Om Meena (T II-3) are gratefully The higher proportion of females generally acknow ledged. led to an accelerated growth rate. In the case of GR, the sex ratio was more REFERENCES balanced. The hypothetical F 2 female number was also higher in IR, being Alam, M. M. 1974. Biological control of 14527.48 in comparison to 4228.9 in GR. insect pests of horticultural crops in GerJ ing (1972) has observed Barbados, pp. 253-261. In: Brathwaite, superparasitism in T. remus. Singh et al. C. W. D., Phelps, R. H. and Bennett, F. (1995) also observed that more females D. (Eds.), Proceedings ofa Symposium were produced by P striaticeps when the on the Protection ofHorticultural Crops host eggs were parasitised solitarily and in Caribbean held at Department of superparasitism resulted in a more balanced Crop Sciences, The University of West sex ratio. They opined that superparasitism Indies, S1. Augustine, Trinidad, April and higher female progeny production 8-11,1974. could be reproductive adaptations of the parasitoids to utilise less suitable hosts for Andrewartha, H. G. and Birch, L. C. (Eds.) production of females. 1954. The Distribution and Abundance ofAnimals. University of Chicago Press, The present experiment indicated that Chicago, 782pp. a higher reproductive rate and a female biased sex ratio could be obtained through Braune, H. J. 1982. Effect of the structure individual rearing. In a mass multiplication of host egg-mass on the effectiveness unit it is not practical to follow individual of an egg parasite of Spodoptera litura rearing method, however, it is necessary (F.) (Lepidoptera: Noctuidae).Drosera, to know the reproductive potential of a 1: 7-16. parasitoid when optimum conditions are provided. With this knowledge it is possible Gerling, D. 1972. The developmental to formulate or improve multiplication biology of Telenomus remus Nixon methods to obtain maximum output, in (Hymenoptera: Scelionidae).Bulietin of terms of reproductive rate and female Entomological Research, 61: 385-388. progeny production. Hernandez, D. and Diaz, F. 1995. Effect of age of the parasitoid Telenomus ACKNOWLEDGEMENTS remus Nixon (Hymenoptera: Scelionidae) on its oviposition capacity The facilities provided by and sex ratio of progeny. Boletin de Dr. S. P. Singh, Project Director, Project Entomologia Venezolana, 10: 161-166. Directorate of Biological Control, Bangalore and the technical assistance Hernandez, D. and Diaz, F. 1996. Effect rendered by Mr. S. C. Kaushik (T II-3) and of age of the host Spodoptera

30 Fertility table ofT remus

Jrugiperda (Smith) (Lepidoptera: (Hymenoptera: Scelionidae) under Noctuidae) on parasitism and sex ratio laboratory conditions. Entomophaga, of progeny of Telenomus remus Nixon 19: 482-492. (Hymenoptera: Scelionidae). Boletin de Entomologia Venezolana, 11: 27-32. Senrayan, R., Velayudhan, R. and Rajadurai, S. 1988. Reproductive Hernandez, D., Ferrer, F. and Linares, B. strategies of an egg parasitoid, 1989. Introduction of Tel enom us remus Trissolcus sp. (Hymenoptera: Nixon (Hymenoptera: Scelionidae) for Scelionidae) on two different hosts. the control of Spodoptera frugiperda Proceedings of the Indian Academy of (Lepidoptera: Noctuidae) in Yaritagua Sciences, Sciences, 97: 455- - Venezuela. Agronomia Tropical 461. Maracay, 39: 4-6. Singh, R. N., Sinha, S. S. and Thangavelu, Krishnamoorthy, A. and Mani, M. 1985. K. 1995. Life-table studies of the egg Investigations on Telenomus remus parasitoid, Psix striaticeps Nixon and Apanteles marginiventris (Hymenoptera: Scelionidae) on the (Cresson) against Spodoptera litura silkworm predator Canthecona (Fabricius) on cabbage. Entomon, 10: furcellata (Pentatomidae, Heteroptera). 277-280. Journal OJ Biological Control, 9: 5-8. Pacheco, D. J. P. and Correa Ferreira, B. Singh, S. P. and JaJali, S. K. 1997. S. 1998. Reproductive potential and Management of Spodopte ra litura longevity of the parasitoid Telenomus (Fabricius) (Lepidoptera: Noctuidae), podisi Ashmead in eggs of different stink pp. 27-65, In: Wightman, J. A. and bug species. Annais da Sociedade Ranga Rao, G. V. (Eds.). Spodoptera Entomologica do Brasil, 27: 585-591. litura in India, Proceedings of the Patel. R. C., Yadav, D. N. and Saramma, National Scientists Forum on P. U. 1979. Impact of mass releases of Spodoptera litura (F) April 2-4, 1996, Chelonus heliopae Gupta and ICRISAT, Asia Center, Patancheru 502 Telenomus remus Nixon against 324, Andhra Pradesh, India. Spodoptera litura (Fabricius). Journal oj Entomological Research, 3: 53-56. Southwood, T. R. E. 1978. Ecological Methods with Particular Reference to Schwartz, A. and Gerling, D. 1974. Adult the Study of Insect Populations. biology of Telenomus remus Chapman and Hall, London. 524 pp.

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