A role for nematocytes in the cellular immune response of the Drosophilid Zaprionus indianus. Balint Z. Kacsoh, Julianna Bozler, Todd A. Schlenke. Biology, Emory University, Atlanta, GA.

   The fruit fly Drosophila melanogaster has served as a model system for understanding innate immune responses such as the humoral induction of antimicrobial peptides by the Toll and Imd pathways. However, the cellular melanotic encapsulation response mounted by D. melanogaster against macroparasites, which is based on hemocyte binding to the foreign object, is poorly characterized and appears to be variable across insect lineages. The genus Zaprionus is a diverse clade of flies imbedded within the genus Drosophila. I have characterized the immune response of Z. indianus against endoparasitoid wasp eggs, which elicit the melanotic encapsulation response in D. melanogaster. I found that Z. indianus is highly resistant to a diverse panel of wasps. Although Z. indianus mounts the canonical melanotic encapsulation response against some wasp species, it can also fight off wasp infection using two other mechanisms D. melanogaster is not known to possess: encapsulation without melanization and non-cellular killing potentially based on wasp egg chorion disruption. Z. indianus produces a large number of hemocytes including nematocytes, which are large fusiform hemocytes absent in D. melanogaster, but which I found in several other species in the subgenus Drosophila. Several lines of evidence suggest these nematocytes are involved in anti-wasp immunity in Z. indianus and in particular in the encapsulation of wasp eggs. Altogether, my data show that the canonical anti-wasp immune response and hemocyte makeup of the model organism D. melanogaster vary across the genus Drosophila.