Reproductive Strategies of 3 Species of Ectoparasitic Wasps Are Modulated by the Response of the Fly Host Sarcophaga bullata (Diptera: Sarcophagidae) to Parasitism

Abstract

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 fly 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 .