PROLONGED OVIPOSITION DECREASES THE ABILITY OF THE PARASITOID LEPTOPILINA-BOULARDI TO SUPPRESS THE CELLULAR IMMUNE-RESPONSE OF ITS HOST DROSOPHILA-MELANOGASTER

The cellular immune response of Drosophila against metazoan parasites is characterized by the production of melanotic capsules comprised mos tly of host blood cells (hemocytes). During the latter part of the ovi positional period of the cynipid wasp parasitoid Leptopilina boulardi, eggs are deposited into host larvae of Drosophila melanogaster that a re more susceptible to destruction by melanotic encapsulation than are eggs laid earlier. The increase in parasitoid mortality is attributed to a decline in the wasp's ability to suppress the host immune respon se. The decrease in active immune suppression is dependent on the repr oductive physiology of the wasp, and this correlates with the extent o f her prior ovipositional experience and not on her chronological age nor on the number of eggs remaining in the ovarioles. Such females wit h prior ovipositional experience which lack the ability to immune supp ress infect far fewer hosts than females with no prior ovipositional e xperience. The reluctance of experienced wasps to infect hosts is not due to egg depletion, but instead is attributed to a depletion in immu ne suppressive substances. Perhaps by ovipositional restraints, retain ing eggs that would otherwise become encapsulated reduces selection pr essure in host populations for specific immune reactivity. (C) 1998 Ac ademic Press.