Defense Reactions of Drosophila Species (Diptera: Drosophilidae) to the Parasite Pseudeucoila bochei (Hymenoptera: Cynipidae)1

Abstract

Previous studies in Europe have shown that various percentages of larvae of Drosophila melanogaster Meigen and D. simulans Sturtevant encapsulate the eggs of the cynipid Pseudeucolia bochei Weld. Similar reactions were found in several strains of D. melanogaster from the northeastern United States. Several other Drosophila species collected in Pennsylvania, New Jersey, Connecticut, and Maine were found also to perform this encapsulation in greater or lesser degree although, in this study, P. bochei was taken only in western Pennsylvania, where its probable host was D. melanogaster. More than 90% of the parasite eggs were encapsulated by larvae of D. busckii Coquillett, of which only 1 strain was tested; D. algonquin Sturtevant and Dobzhansky also proved highly immune to this cynipid; but D. affinis Sturtevant proved only moderately successful in encapsulating the parasite's eggs. D. athabasca Sturtevant and Dobzhansky, D. immigrans Sturtevant, and D. robusta Sturtevant made only partial reactions involving hemocyte clumping and melanization, and in the last 2 of these species the reactions were rather weak and very rare. No reaction at all was observed in D. putrida Sturtevant. Although no hemocyte reaction was observed in either D. paramelanica Patterson or D. nigromelanica Patterson and Wheeler, both these species appear highly immune to P. bochei, as the parasite's eggs often failed to hatch or, if they hatched, the larvae died. Whether a humoral reaction was involved or whether these hosts are otherwise unsuitable for development of P. bochei is not known. The possible role of mimicry by parasites in the evolution of defense mechanisms is discussed.