Pre- and post-imaginal experience in a specialist parasitoidDiadromus pulchellus (Hym.: Ichneumonidae)

The locomotory behaviour of femaleDiadromus pulchellus Wesm. (Ichneumonidae), a specialist endoparasitoid ofAcrolepiopsis assectella Zell. chrysalids, was analyzed in an olfactometer. Three parameters were measured: distance walked, number of turns and female distribution. The volatiles emitted by the larval frass ofA. assectella which feeds exclusively onAllium plants modified all three parameters. When females were placed in contact with frass and/or with the host before the olfactometer test, the number of turns was lower in comparison to that of naive females tested without prior contact with the host and/or its frass. 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 was found because parasitoids emerging from the chrysalids of a non-host moth,P. interpunctella, responded to the frass volatiles of the usual host,A. assectella, in the same way as parasitoids reared on this latter host.