PREIMAGINAL AND POST-IMAGINAL EXPERIENCE IN A SPECIALIST PARASITOID DIADROMUS-PULCHELLUS (HYM, ICHNEUMONIDAE)

The locomotory behaviour of female Diadromus pulchellus Wesm. (Ichneum onidae), a specialist endoparasitoid of Acrolepiopsis assectella Zell. chrysalids, was analyzed in an olfactometer. Three parameters were me asured: distance walked, number of turns and female distribution. The volatiles emitted by the larval frass of A. assectella which feeds exc lusively on Allium plants modified all three parameters. When females were placed in contact with frass and/or with the host before the olfa ctometer test, the number of turns was lower in comparison to that of naive females tested without prior contact with the host and/or its fr ass. This indicated that the trajectory of experienced females towards the odour source was more direct. Associative learning is a possible mechanism behind this change. No evidence of pre-imaginal experience w as found because parasitoids emerging from the chrysalids of a non-hos t moth, P. interpunctella, responded to the frass volatiles of the usu al host, A. assectella, in the same way as parasitoids reared on this latter host.