DISPERSAL AND PARASITIZING ABILITIES OF EUPELMUS-VUILLETI (HYMENOPTERA, EUPELMIDAE) WITHIN A COLUMN OF COWPEA SEEDS

Eupelmus vuilleti (Crawford) is an ectoparasitoid of the seed-eating b eetle Bruchidius atrolineatus (Pic), which is an important pest of sto red cowpea, Vigna unguiculata Walp, seeds in West Africa. Herein, we i nvestigated the dispersal abilities of females within columns of seeds to assess the potential of E. vuilleti as a biological control agent of bruchids in cowpea granaries. The influence of host presence togeth er with the 2 abiotic factors light and gravity on parasitoid movement and parasitization efficiency were analyzed. E. vuilleti females were able to travel through large seed masses and parasitize hosts located at the end of the seed column opposed to their introduction zone. Par asitoid movement was stimulated by light. E. vuilleti females exhibite d a negative geotropism. Females introduced at the bottom of the seed column dispersed more and parasitized more hosts than females introduc ed at the top. Host presence had some influence on the dispersal of th e parasitoids within the seed column at a host density of 10 infested seeds for 16,000-18,000 uninfested seeds. This depended on female intr oduction zone because gravity was the major factor influencing dispers al. The possible applications of these results for biological control of bruchids in cowpea granaries are discussed.