Institut de Recherche sur la Biologie de l'Insecte, UPRESA-CNRS 6035, Faculté des Sciences, Parc de Grandmont, 37200 Tours, France.
The solitary endoparasitoid Diadromus pulchellus (Hym.: Ichneumonidae) uses a chemical signal from the silk cocoon to recognize and accept its host pupa, Acrolepiopsis assectella (Lep.: Acrolepiidae). This signal is detected by the parasitic wasp through contacts between its antennae and the cocoon. An aqueous extract of cocoons containing 4 purified glycopolypeptides (90, 86, 78, 70 kDa) acts as an acceptation signal. Complementary morphological and ultrastructural studies on antennal receptors were realised in order to identify the contact chemosensory sensilla which could perceive the kairomonal polypeptides. Three types of sensilla have been shown to have a chemosensory function (presence of one or several apical pores, presence of dendrites within the cuticular expansion). In order to characterize the gustatory function of the sensory organs implicated in the cocoon kairomon perception, electrophysiological studies were carry out on this three ypes of sensilla. Two types of gustatory chemosensory sensilla present on D. pulchellus female antennae would be involved in the perception of this proteinaceous kairomonal signal. One of them, a multiporous sensilla observed on the ventral face of the last fifteen antennomeres and only in the females, presented the most important activity in terms of number of action potentials. Therefore, this sensilla might be the one implicated in the perception of this proteinaceous signal triggering the host —acceptance behavior.