Abstract.The braconid parasitoidAsobara tabidaNees attacks larvae of severalDrosophilaspecies in fermenting substrates. Northwestern and central European populations of the parasitoid attack mainlyD.subobscuraCollin. Southern European parasitoids attack mainlyD.melanogasterMeigen. Larvae of this last species can defend themselves against parasitoids by encapsulating the parasitoid egg. Parasitoids from southern European populations are better able to resist encapsulation of their eggs than their northwestern and central European conspecifics. The eggs of southern European parasitoids appear to have a ‘sticky’ egg chorion. As a result of this ‘stickiness’ the eggs become embedded in host tissue where they are not completely covered by the host's blood cells. This leads to, at most, partial encapsulation of the egg. Parasitoid larvae can escape from partially closed c