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Gregarious development of the solitary endo-parasitoid, Microplitis rufiventris in its habitual host, Spodoptera littoralis

Hegazi, E.M., Khafagi, W.E.
Journal of applied entomology 2005 v.129 no.3 pp. 134-141
Microplitis, Spodoptera littoralis, parasitoids, host-parasite relationships, superparasitism, larvae, insect development, egg hatchability, viability, mortality, temperature, host preferences
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 degrees 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 degrees C than at 27 degrees C. The results of the present study are useful in understanding the evolution of life-history strategies and host range in parasitic hymenoptera.