Two non-linked genes for specific virulence of Leptopilina boulardi against Drosophila melanogaster and D-yakuba

The developmental success of Leptopilina boulardi parasitoids within host s pecies of the melanogaster subgroup is determined mainly by their ability t o suppress the host immune reaction (virulence). Host resistance and parasi toid virulence are genetically variable in both partners. A gene for specif ic resistance against L. boulardi (Rlb) has been identified in Drosophila m elanogaster, and a gene for the immune suppression (IS) of D. melanogaster has been identified in L. boulardi. To understand the evolution of the IS g ene, we determined its specificity regarding potential hosts of the melanog aster subgroup. It did not affect the virulence against any other species o f the melanogaster subgroup and was called ISm for immune suppression of D. melanogaster. Another gene (ISy), non-linked to the gene ISm, was characte rized for the specific immune suppression of D. yakuba. These results sugge sting that natural selection for virulence against one host species does no t influence the evolution of virulence against another will allow us to dev elop pertinent hypotheses concerning the evolution of this character which is expected to drive the evolution of the parasitoid toward narrow host spe cialization.