Comparative Study of Immune Competence and Host Susceptibility in Drosophila melanogaster Parasitized by Leptopilina boulardi and Asobara tabida

Abstract

Larvae of an immune-reactive (R) strain of Drosophila melanogaster readily encapsulated and killed the eggs of 2 species of parasitic wasp, Leptopilina boulardi and Asobara tabida. High pressure liquid chroma- tography with electrochemical detection identified 5,6-dihydroxyindole (DHI) and N-acetylarterenone (NAA) in the hemolymph during parasite encapsulation, indicating that the capsules enveloping the parasites are comprised of both eumelanin and sclerotin. In larvae of a host strain susceptible (S) to L. boulardi, DHI and NAA were absent, and hemolymph catecholamine profiles from these hosts resembled those of nonparasitized controls. Susceptibility was determined to be species specific for L. boulardi, because S-strain larvae were highly immune reactive against A. tabida. As with reactive R-strain hosts, DHI and NAA were detected in the he- molymph from immune-reactive S-strain larvae when they were encapsulated by A. tabida. These observations, together with previous studies, indicate that the immune response initiated by larvae of D. melanogaster against different parasites involves similar cellular and biochemical responses. The virtual absence of immune reactivity in the S strain against L. boulardi suggests these otherwise immune competent hosts are unable to recognize this parasite as a foreign entity, or that the wasp actively suppresses the cellular encapsulation response of this host strain. These investigations highlight the complexity of insect host-parasite relationships that involve the co- evolution of varied reciprocal cellular, molecular, and biochemical strategies.