INFLUENCE OF PREEMERGENCE EXPERIENCE ON RESPONSE TO HOST AND HOST-PLANT ODORS IN THE LARVAL PARASITOID EUPELMUS-VUILLETI

The response to different host and plant species odours was investigated in Eupelmus vuilleti (Crw). This hymenopteran is a solitary ectoparasitoid of several species of bruchids developing inside Leguminosae seeds. The locomotor behaviour of females reared on Bruchidius atrolineatus (Pic) larvae developing in Vigna unguiculata (Walp) seeds was analysed using a tubular olfactometer. Females showed a specific sensitivity to the semiochemicals emanating from the host and the seed species on which they had developed. Odours from V. unguiculata seeds were attractive to the parasitoid and stimulated their locomotor activity. Odours from Vigna radiata (Wil) seeds had no effect on the locomotor behaviour. Odours from B. atrolineatus larvae were attractive to the females whereas odours from Callosobruchus maculatus (Fab), another bruchid species, had no effect. By isolating the females from the seed and the host at different developmental stages, we found that the specific sensitivity observed resulted from an early adult learning. This learning which occurs before the emergence from the seed while the image is in the larval chamber of its host is dependent on contact with the seed and the host larval remains.