SPECIFICITY OF ODOR MEDIATED AVOIDANCE OF COMPETITION IN DROSOPHILA PARASITOIDS

Although there are many examples of the role of volatile infochemicals in interactions between trophic levels of insect communities, surpris ingly little is known of volatile interactions between species within the third trophic level. Recently it was found that Leptopilina hetero toma, an endoparasitoid that attacks Drosophila larvae, avoids one typ e of patches (decaying stinkhorn mushrooms) when parasitoids of anothe r species (L. clavipes) are present on these patches. L. heterotoma is able to smell the presence oft. clavipes from a distance (Fig. 1). In this paper we investigate the source of the odour that induces avoida nce behaviour, by varying the host species and parasitoid species pres ent on stinkhorn mushrooms, and by using another type of patch (sap-fl uxes of wounded trees). L. heterotoma was found to avoid stinkhorn pat ches with conspecific as well as heterospecific parasitoids (Fig. 2). Hosts had to be present in the patch to elicit avoidance, but avoidanc e behaviour was also found with another host species present in the pa tch (Pig. 3). No avoidance behaviour was found with sap-flux patches w ith hosts and parasitoids on them (Pig. 4). Avoidance of stinkhorn pat ches only occurred when the parasitoids present on the patch were able to contact hosts (Figs. 5 and 6). The exact source of the odour that elicits avoidance is still unclear, so that one can only speculate on the function of the signal. However, there is a clear benefit to the r eceiver, because it is able to avoid superior competitors. Avoidance c an lead to non-aggregated parasitoid distributions. The importance of avoidance behaviour for population dynamics and stability of parasitoi d-host systems is discussed.