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Earlier research has shown that the koinobiont parasitoid, Microplitis rufiventris, attacks and can develop on early instars of Spodoptera littoralis larvae with preference to third instars. However, the present study was carried out using the newly moulted sixth instar larvae at two different temperatures (20 ± 1 and 27 ± 1°C) to study the developmental interaction between the parasitoid and the last instar host larvae. Parasitoid eggs laid in singly parasitized host larvae invariably died. As the number of parasitoid eggs/host larvae increased, the proportion of eggs that hatched and number of viable parasitoid larvae successfully reached to their final instar increased. The effect of superparasitization seems to be dose (no. of eggs + parasitoid factors)-temperature-dependent. The results demonstrate a kind of‘Allee effect’ suggesting that superparasitized last instar S. littoralis larvae provide a better host environment than singly parasitized hosts for the parasitoid, M. rufiventris. This may be due to host's hormone and/or low dose of factors injected with parasitoid eggs. The supernumerary individuals of wasp larvae developed normally to the point of emergence but most did not successfully emerge from the host. The improvement of both hatchability and post-embryonic development of parasitoid wasp was significantly (P < 0.01) greater at 20°C than at 27°C. The results of the present study are useful in understanding the evolution of life-history strategies and host range in parasitic hymenoptera. [ABSTRACT FROM AUTHOR]

The solitary endoparasitoid,Microplitis rufiventris, attacks and can develop in earlier instars ofSpodoptera littoralislarvae with preference to third-instar larvae. We used the last stadium (sixth instar), a stage which is not naturally parasitized. The newly moulted larvae (0–3 h old) of this stadium were more acceptable for parasitization by the wasp females than the older ones (24 h old). Parasitization byM. rufiventriswasp of last instarS. littoralislarvae leads to dose (no. of eggs + parasitoid factors)-dependent effects which were more pronounced at 20°C than at 27°C. A single oviposition into a sixth instar host larva resulted in normal development of the host. However, superparasitization increased the proportions of developmentally arrested hosts and number of live wasp larvae. Development of supernumerary individuals of the parasitoid in the host larva leads to dose-related adverse effects on host growth and development. The present study may provide interesting opportunities for studying the physiological bases of host–parasitoid interactions and parasitoid intra-specific competition in the biological system considered. [ABSTRACT FROM AUTHOR]