Interspecific competition between two parasitoid species of bruchid larvae, Eupelmus vuilleti (Crw) and Dinarmus basalis (Rond.) (Hymenoptera : Eupelmidae, Pteromalidae): importance of host density and quality on the reproductive success of the two species.

Dinarmus basalis (Rond.) and Eupelmus vuilleti (Crw.) are two sympatric par asitoid species of bruchid larvae in West Africa. D. basalis females avoid to lay on hosts parasitised by E. vuilleti, whatever the age of the immatur e parasitoid present on the host. E. vuilleti immatures have high survival probabilities in interspecific competition, and the femelles do not avoid t o lay on hosts parasitised by D. basalis. When host density is low, the pre sence off. vuilleti females induces significant modifications in the D. bas alis females reproductice activity, and a decrease in the offspring surviva l probability of this last species. When host density is high, interspecifi c competition is limited and a shared exploitation of the available hosts s eems to occur between the two species. The adaptive significance of the exh ibited strategies is discussed.