GEOGRAPHICAL VARIATION IN HABITAT CHOICE AND HOST SUITABILITY IN THE PARASITOID ASOBARA-RUFESCENS

In the Netherlands, Asobara rufescens (Forster) (Hymenoptera: Braconid ae) is a parasitoid of drosophilid larvae in decaying plant material. In several places in the Mediterranean, parasitoids looking very simil ar to A. rufescens were collected on fermenting substrates a hybridiza tion experiment showed that the parasitoids were indeed A rufescens. I n an olfactometer Portuguese A. rufescens do not have a preference for either the odour of yeast or decaying leaves, while their Dutch consp ecifics prefer the odour of decaying leaves. The survival probability of Portuguese A. rufescens in Drosophila melanogaster Meigen (Diptera: Drosophilidae), a species typical for fermenting substrates, is much higher than the survival probability of Dutch A. rufescens in this hos t species.It is hypothesized that decaying plant material may be unsui table for drosophilid larvae during part of the year in the Mediterran ean, forcing A. rufescens there to broaden its microhabitat choice. Th e use of fermenting substrates brings A. rufescens in contact with its sibling A. tabida Nees, a species typical for fermenting substrates i n most of Europe. Portuguese A. rufescens appear to be genetically iso lated from A. tabida. In the Netherlands, where the two species occupy different microhabitats, there is only a premating barrier.