ENTOMOPHAGA 35 (3), 1990, 329-333

I N F L U E N C E O F L A B O R A T O R Y H O S T S O N T H E B I O L O G I C A L A T T R I B U T E S O F C H E L O N U S B L A C K B U R N I [HYM. : B R A C O N I D A E ]

PRADYUMN KUMAR & CHANDISH R. BALLAL

Biological Control Centre, Post Bag 2491, H.A. Farm Post, Bellary Road, Bangalore-560 024, India (9

Among 6 laboratory hosts tested, the egg-larval parasitoid Chelonus blackburni Cameron completed its development in only 3; Corcyra cephalonica Stainton, Phthorimaea operculella (Zeiler) and Achroia grisella (Fabricius). The parasitoid failed to develop in Spodoptera litura (Fabricius), Galleria mellonella L. and Sitotroga cerealella (Olivier). The development period of the parasitoids obtained from permissive hosts correspond to the development period of their hosts. Development period of P. operculella, A. grisella and C. cephalonica were 24.7 _+ 2.0, 39.5 + 2.1 and 50.5 + 4.1 days respectively while the development period of the parasitoid reared from these hosts were 25.8 _ 1.6, 36.4 +_ 3.5 and 42.5 ___ 3.5 days respectively. The fecundity of the parasitoids reared on A. grisella, P. operculella and C. cephalonica were 365.2 + 52.8, 287.9 +_ 101.9 and 248.7 + 50.8 respectively. The size of the parasitoids reared from the above 3 hosts also followed the similar trend. However, no significant difference was observed on the percent parasitism and the longevity of the parasitoids reared on different hosts. This study was conducted at a temperature of 24 + 2 ~ and 60 + 5 % RH.

KEY-WORDS : Chelonus blackburni, hosts influence.

Chelonus blackburni Cameron, an egg-larval parasitoid of cotton bollworms was found to bred well on the laboratory host Ephestia kuhniella Zeller, in USA (Noble & Hunt, 1937). In India, the common meal moth Corcyra cephalonica Stainton and Potato Tuber Moth, Phthorimaea operculella (Zeller) have been used as laboratory hosts for this parasitoid. Morghan & Crumb (1941) have reported C. blackburni parasitising 19 lepidopterous and dipterous species. Rao et al. (1979) exposed I0 lepidopterous hosts out o f which the development of the parasitoid was completed in 8 species. The quality of the parasitoid reared on different hosts vary depending upon the quantity and quality of the materials, the host provide. We therefore used 6 laboratory hosts to study the percent parasitism, development period, longevity, fecundity and size of the progeny of C. blackburni with a view to determine most suitable laboratory host fo r the mass rearing of this parasitoid.

MATERIALS AND METHODS

Six laboratory hosts viz. C. cephalonica on broken sorghum, P. operculella on potato tubers, Sitotroga cerealella (Olivier) on paddy, Spodoptera litura (Fabricius) on artificial

(t) Contribution No 46001 of Biological Control Centre (NCIPM), Bangalore.

330 PRADYUM KUMAR & CHANDISH R. BALLAL

diet by Nagarkatti & Satya Prakash (1974), and Galleria mellonella L. and Achroia grisella (Fabricius) on a common artificial diet by Waterhouse (1959) were reared in the laboratory. In a preliminary study the eggs of these 6 hosts were parasitized by C. blackburni. The deposition of parasitoid egg was confirmed in all the 6 species by dissecting the eggs. One hundred fifty freshly laid eggs of each species were pasted on cards and exposed to individual parasitoid in 2.5 cm x 15 cm glass vials. A wax-coated card bearing 5-6 droplets of 20 percent honey was inserted in each vial, The treatments were replicated 6 times.

After 24 h of exposure the parasitoids were removed and the host eggs were observed for hatching. Within 4 days the host eggs hatched normally in all the species except in ease of S. litura and S. cerealella. These eggs were dissected under binocular microscope to determine the reason. The neonate larvae of the remaining 4 species were bred on their respective diets at 24 ___ 2 *C and 60 + 5 % RH. The parasitoids emerged, from only 3 hosts viz. C. cephalonica, P. operculella and A. grisella. The total number of parasitoids and hosts emerged from each of these 3 species were collected and their development period recorded.

For the study of longevity and fecundity 10 parasitoids of the progeny obtained from each host were randomly selected and transferred individually in 2.5 cm x 15 cm glass vials. Each parasitoid was offered 70 Corcyra eggs for parasitization every day till the parasitoid died. The eggs parasitized by each parasitoid during its life span were reared on broken sorghum in 10cm x 15 cm plastic containers. The parasitoid emerged up to 55 th day after the day of last parasitized egg-card added, were recorded.

Twelve parasitoid adults were randomly selected from the progenies obtained from each host and their length and breadth measured. Length and breadth of 12 eggs of each hosts were also measured. Size index of parasitoid and host eggs were determined by multiplying length with breadth. Twelve full grown larvae of each host species were also weighed individually.

RESULTS AND DISCUSSION

The eggs of S. cerealella and S. litura succumbed to parasitization and failed to hatch. In S. litura the host embryo developed almost completely into 1 st instar larva, and died within the egg shell. In S. cerealella no development of host embryo occurred and the eggs were found shrivelled. No stage of parasitoid could be located in both the species. In case of G. mellonella all the parasitized host eggs hatched and developed normally till adult stage but the parasitoid larvae did not emerge. This suggests the possibility of encapsulation of the parasitoid during one or the other immature stage. In the remaining 3 species the parasitoid successfully completed their development and emerged when the host reached prepupal stage.

Development period of parasitoid was found to be influenced by the development period of host. There were observed significant differences among the development periods of hosts and correspond to them the development period of parasitoid (table 1). A high correlation (r = 0.99) was observed between the development time of hosts and parasitoid (fig. 1).

Number of parasitoid adults emerged was considered as the number of eggs parasitized. Maximum per cent parasitization of 36.1 was observed in C. cephalonica and minimum of 30.7 in P. operculella, however, no significant difference was observed in the per cent parasitization of these host species. Longevities of the parasitoids bred on these 3 hosts species were also not significantly different.

H O S T S I N F L U E N C E O N CHELONUS BLACKBURNI 331

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332 PRADYUM KUMAR & CHANDISH R. BALLAL

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The size and fecundity of the parasitoid was observed maximum in A. grisella and minimum in C. cephalonica. A high correlation (r = 0.93) was observed between size and the fecundity of the parasitoid obtained from these hosts. A direct relation between the size of the host and the size of the parasitoid develops on it has been observed in large number of cases (e.g. Sweetman, 1958 ; Charnov et al., 1981 ; Mendel, 1986). In our study this relationship did not occur in C. cephalonica. The size of eggs and larvae were largest in case o f A. grisella, medium in C. cephalonica and smallest in case of P. operculella but the size of the parasitoid obtained from C. cephalonica were smallest (table 1). The development period of C. cephalonica is almost 2 times of the development period of P. operculella. It is possible that in C. cephalonica the parasitoid, after development, remains quiescent till the host reached its prepupal stage. During the quiescence the parasitoid utilizes its stored food for the basal metabolism and therefore, emerged as a smaller and less fecund adult.

Since the parasitoid develop much faster in P. operculella when compared with other 2 hosts and other biological attributes are also moderately good the authors feel that this host can be proved most suitable for the mass rearing of C. blackburni.

ACKNOWLEDGEMENTS

The authors are grateful to Dr. S. P. Singh, Project Coordinator and Head, Biological Control Centre, Bangalore for providing the necessary facilities required for the studies and Mrs. Shashikala S. Kadam for her technical assistance.

HOSTS INFLUENCE ON CHELONUS BLACKBURNI 333

RESUMI~

Influence des h6tes de laboratoire sur les param&res biologiques de Chelonus blackburni [Hym. : Braconidae]

Parmi les 6 h6tes de laboratoire essay6s, le parasito'ide Chelonus blackburni n'ach6ve son d6veloppement que dans les 3 suivants : Corcyra cephalonica Stainton, Phtorimaea operculella (Zeller) et Achroia grisella (Fabricius). I1 6choue dans Spodoptera litura (Fabricius), Galleria mellonella L. et Sitotroga cerealella (Olivier). La dur6e d'6volution des parasitoides obtenus d'h6tes la permettant correspond fi celle de leurs h6tes. La dur6e de d6veloppement de P. operculella, d'A. grisella et de C. cephalonica 6tait respectivement de 24,7 + 2,0 ; de 39,5 -I- 2,1 et de 50,5 _+ 4,1 jours, tandis que celle du parasitoide 61ev6 des h6tes &ait respectivement de 25,8 _+ 1,6; de 3 6 , 4 _ 3,5 et de 42,5 +_ 3,5jours. La f6condit6 des parasitoides issus de A. grisella, P. operculella et C. cephalonica &ait de 365,2 + 52,8 ; de 287,9 + 101,9 et de 248,7 _+ 50,8 oeufs. La taille des parasitoides issus des 3 lots ci-dessus suivait une tendance similaire. Cependant, on n'observait aucune diff6rence signifi- cative dans le pourcentage de parasitisme et la long6vit6 des parasitoides en fonction de l'h6te. Cette 6tude a 6t~ conduite fi la temp6rature de 24 +__ 2 *C et 60 ___ 5 % d'H.R.

MOTS CLIPS : Chelonus blackburni, influence des h6tes.

Received : 20 December 1988 ; Accepted : 23 March 1989.

REFERENCES

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Mendel, Z. - - 1986. Hymenopterous parasitoids of bark beetles [Scolytidae] in Israel : Relationships between host and parasitoid size, and sex ratio. - - Entomophaga, 31, 127-137.

Morghan, A. C. & Crumb, S. E. - - 1914. The tobacco split worm. - - Bull. U.S. Dept. Agric. Washington. D.C., 59, 7.

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Noble, L. W. & Hunt, W. T. - - 1937. Imported parasites of pink bollworm at Presidio, Tex. 1932-36. - - J . Econ. Entomol., 30, 842-844.

Rao, K. J., Thontadarya, T. S. & Rangadhamaiah, K. - - 1979. A note on the survival and parasitism of the egg-larval parasite Chelonus blackburni Cameron [Hym. : Braconidae] on some lepidopterous hosts. - - Current. Res., 8, 48-50.

Sweetman, H. L. - - 1958. The Principles of Biological Control. - - Wm. G. Brown Co., Dubuque, Iowa, 560 pp.

Waterhouse, D. F. - - 1959. Axenic culture of wax moth for digestion studies. - - Ann. N. Y. Aead. Sci., 77, 283-289.