Visual and olfactory cues perceived during reprodutive behaviour by the fruti flies parasitoid Psyttalia concolor (Szèpligeti) (Hymenoptera: Braconidae)

The reproductive behaviour of Psyttalia concolor (Hymenoptera: Braconidae) was studied through ethological bioassays using testing arenas and still-air olfactometers. The male courtship behaviour was high-speed video-recorded and analysed. The costs and benefits of male-male sexual approaches were evaluated. Concerning host-seeking behaviour, the P. concolor innate preferences for different hosts or visual cues were investigated, as well as its ability to prefer a given stimulus after a training experience (i.e. sensitization, associative learning). As regards to olfactory cues, the parasitoid preferences for different tephritid-infested fruits were tested using still-air arenas. The behavioural responses of the parasitoid under choice-conditions were analyzed comparing different fruits (both healthy and infested) and specially made fruit dummies. Volatiles emitted by healthy and medfly-infested fruits were SPME-sampled and analyzed by gas chromatography-mass spectrometry (GC-MS). The attractiveness of the identified volatiles was assessed and their electrophysiological activity was analyzed through gas-chromatography coupled with electroantennography (GC-EAD). P. concolor preferred infested peaches and apples over healthy ones, either when visual and olfactory or only olfactory cues were given. Nine compounds were found as exclusive of infested peaches, with respect to healthy ones, and seven of them evoked electrophysiological responses. In apples only quantitative changes in volatile emissions were observed after the medfly infestation. The emissions of 1-butyl butylate, 1-hexyl acetate and 1-butyl esanoate increased in infested apples, whereas 1-hexyl (E)-2-methyl butenoate decreased significantly. Among apple volatiles, 1-butyl butylate, 2-methyl-1-butyl acetate, 1-hexyl acetate, 2-methyl-1-butyl 2-methylbutanoate, 1-butyl hexanoate and 1-hexyl (E)-2-methyl butenoate elicited responses in female antennae. Synthetic blends reproducing the odors emitted by infested peaches and apples elicited strong attraction towards P. concolor females. For both fruits, the blend attractiveness was mainly due to some specific electrophysiological active chemicals: ethyl octanoate, decanal and 4-decanolide for peach, and 1-butyl butylate and 1-butyl hexanoate for apple. The responses induced by the identified fruit volatiles to P. concolor females allow us to suppose that they play a role as short-range kairomones during host location and, therefore, have the potential to improve biological control programs. Besides field applications, these molecules could be used to improve mass-rearing techniques of P. concolor, since these chemicals may be useful to enhance parasitization rates on tephritid hosts.