AGGREGATIVE RESPONSES OF PARASITOIDS AND PARASITISM IN POPULATIONS OF DROSOPHILA BREEDING IN FUNGI

In a community of Drosophila, breeding in the stinkhorn, Phallus impudicus, the distributions of adult parasitoids, hosts, and parasitism were studied to evaluate the relevance of aggregation of parasitism with respect to the stabilization of parasitoid and host populations in a natural habitat. Density-dependent parasitism was found at both the smallest spatial level, i.e. clumps of mushrooms, and at the largest spatial level, i.e. the study area. Howevere, host density did explain but 37% of the variation at the smallest level and not more than 14% at the population level. The overall distribution of parasitism could be described by a negative binomial with clumping parameter k less than 1, indicating aggregation of parasitism might be a possible stabilizing force in this community. The origin of the aggregation of parasitism at the population level is a Poisson distribution of parasitoid attacks within patches combined with a gamma distribution of adult parasitoids among patches. We discuss factors ultimately determining the risk of being parasitized within a patch and the origin of the distribution of adult parasitoids.