Behavioral and electrophysiological responses of the parasitic wasp Psyttalia concolor (Szépligeti) (Hymenoptera: Braconidae) to Ceratitis capitata-induced fruit volatiles

Psyttalia concolor (Szépligeti) is a koinobiont larval-pupal endoparasitoid of many Tephritidae of great economic importance, such as the medfly, Ceratitis capitata (Wiedemann). In several species of parasitoids it has been demonstrated that the mated females are strongly attracted by specific volatiles from insect-damaged plants. Yet the role of olfactory cues deriving from C. capitata-infested fruits on the female’s decision during the P. concolor host location was poorly investigated. In the present study, the responses of P. concolor females to either healthy or C. capitata-infested fruits was studied through behavioral assays. Volatiles emitted by healthy and infested fruits were SPME-sampled and analyzed by gas chromatography-mass spectrometry (GC-MS). The electrophysiological activity (GC-EAD) of characteristic volatiles emitted from both fruits was analyzed through gas-chromatography coupled with electroantennography (GC-EAD) and the attractiveness of the EAD-active volatiles evaluated. 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 consistently. 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 attractants during host location.