Reproductive strategies of 3 species of ectoparasitic wasps are modulated by the response of the fly host Sarcophaga bullata (Diptera: Sarcophagidae) to parasitism

Envenomation by the ectoparasitic wasps Nasonia vitripennis (Walker), Muscidifurax zaraptor Kogan & Legner, and Trichomalopsis near americana (Hymenoptera: Pteromalidae) caused rapid death (within 24 h) or a developmental arrest in the ny host Sarcophaga bullata Parker (Diptera: Sarcophagidae). The dominant response of S. bullata to envenomation by any of the 3 wasps was an arrested or retarded development, the duration of which varied with wasp species and weight of the host. Although most flies (>50%) in arrested development did show some progression in pharate adult development, it was delayed by several days compared with unenvenomated flies and none eclosed as adults. A positive relationship was observed between the number of eggs deposited per host by the 2 gregarious wasps N. vitripennis and T. near americana and the duration of the induced developmental arrest. Such a relationship was not observed for the solitary wasp M. zaraptor, because larval fighting between 1st-instar siblings prohibited more than 1 adult wasp emerging from each fly puparium. Envenomation by all wasps resulted in elevated hemolymph lipid titers in S. bullata within 1-2 d after venom injection. The peak in host hemolymph lipid content correlated positively with clutch sizes for N. vitripennis and T. near americana, but not for M. zaraptor. This suggests that alterations in fly lipid metabolism are linked to developmental events associated with host arrestment that are essential to progeny development of the 2 gregarious species but that are not important to a solitary parasite such as M. zaraptor.