EXPERIMENTAL PARASITOLOGY 70,4f+475(1!9!20) Leptopilina heterotoma and L. boulardi: Strategies to Avoid Cellular Defense Responses of Drosophila melanogaster

lardi: Strategies to avoid cellular defense responses of Drosophila melanogaster. Experi-mental Parasitology 70,466-475. Eggs of three strains of the cynipid parasitoid Leptopilina heterotoma and a Tunisian strain (G317) of L. boulurdi are not encapsulated by hemocytes of Drosophila melanogaster hosts, but the eggs of a Congolese strain (L104) of L. boulurdi are encapsulated. To determine the reason for the difference in host response against the parasitoid eggs, lamellocytes (hemocytes that encapsulate foreign objects and form capsules around endogenous tissues in melunotic tumor mutants) were examined in host larvae parasitized by the five Leptopilina strains. Parasitization by the three L. heterotoma strains affected the morphology of host lamellocytes and suppressed endogenous melanotic capsule formation in melunotic tumor hosts. L104 did not alter the morphology of host lamellocytes nor block tumor formation in melunotic tumor mutant hosts. The morphology of some lamellocytes was affected by G317 parasitization but host lamellocytes were still capable of forming melanotic tumors and encapsulating dead supernumerary parasitoid larvae. There-fore, the eggs of strains affecting lamellocyte morphology are protected from encapsulation by the host’s blood cells. L. heterotoma eggs float freely in the host hemocoel but L. boulardi eggs are attached to host tissue surfaces. Lamellocytes cannot infiltrate the attach-ment site so the capsule around the L104 egg remains incomplete. The wasp larva uses thi