INFOCHEMICALS INFLUENCING THE HOST FORAGING BEHAVIOR OF DAHLBOMINUS-FUSCIPENNIS, A PUPAL PARASITOID OF THE EUROPEAN SPRUCE SAWFLY (GILPINIA-HERCYNIAE)

The chalcidoid wasp Dahlbominus fuscipennis Zett. (Hymenoptera: Euloph idae) parasitises pupae of the European spruce sawfly Gilpinia hercyni ae Htg. (Hymenoptera: Diprionidae). In tl-lis parasitoid-host system t he role of infochemicals for successful parasitisation was studied. Ol factometer experiments and dual choice bioassays in petri dishes showe d that D. fuscipennis was not attracted by volatiles from a plant-host complex consisting of spruce, sawfly larvae and pupae. On the other h and, odours from needles of Picea abies (L.), that were collected from the ground, attracted D. fuscipennis to the habitat of the sawfly. Vo latiles from host pupae were not attractive, whereas a contact kairomo ne from sawfly pupae elicited frequent antennal drumming, a behaviour that indicates host recognition. This contact kairomone was extracted with methanol from the outer cocoon layer of the pupa. The kairomone i s not produced by the silk glands of the last instar larva spinning th e cocoon, since a methanolic extract of silk gland secretion did not e licit any response in D. fuscipennis. Further bioassays revealed that non-volatile components of the integument of the prepupa within the co coon also elicited antennal drumming. We suggest that chemicals of the prepupal integument diffuse from inside the cocoon to the outside whe re they inform the parasitoid on the suitability of the host.