Interspecific relations between two sympatric species of hymenoptera, Dinarmus basalis (Rond) and Eupelmus vuilleti (Crw), ectoparasitoids of the bruchid Callosobruchus maculatus (F)

Dinarmus basalis (Rond) and Epelmus vuilleti (Cnv) are rico Hymenopteran sp ecies, which are solitary ectoparasitoids of bruchid larvae. In the presenc e of seeds of Vigna unguiculata (Walp) containing hosts parasitized by E, v uilleti, a high percentage of D. basalis females avoided multiparasitism wh atever the age of the eggs or the larvae present on the host. The least avo idance was observed when the hosts were parasitized by E. vuilleti 30 min b eforehand. This avoidance behavior is adaptive and is related to the low su rvival chances of the D. basalis larvae when they are in interspecific comp etition with E. vuilleti larvae. The analysis of the behavior of D. basalis demonstrated that the avoidance of multiparasitism could be due to the per ception of two signals; an external signal deposited on the surface of the seeds during the E. vuilleti oviposition phase and an internal signal due t o the presence of the eggs and larvae at the surface of the hosts. E. vuill eti females did not avoid multiparasitism and multiparasitized the hosts be aring D. basalis eggs or larvae. The behavior of E, vuilleti females was no t disturbed by the presence of its competitor: Under these conditions of in terspecific competition, the survival chances of E. vuilleti larvae were ve ry high whatever the age of its competitor D. basalis. The two species of p arasitoids could move in a column containing healthy seeds of V. unguiculat a and patches with seeds containing parasitized or unparasitized larvae. Th e distribution of D. basalis females introduced into these columns depended on the host quality. They avoided the patches containing the hosts parasit ized E. vuilleti and were found in the patches with healthy hosts. The beha vior of E. vuilleti females was very different; the distribution of rite fe males and th parasitism min multiparasitism rates were not affected by the quality of the hosts present in the patches. The adaptive significance of t he behaviors of these two species was analyzed in relation to the survival chances of their offspring.