Olfactory responses of Drosophila suzukii parasitoids to chemical cues from SWD-infested fruit

Since Drosophila suzukii (Diptera: Drosophilidae; SWD) became a worldwide pest of soft-skinned fruits, multiple mitigation strategies alternative to insecticides have been explored. Among these, the search for biological control agents has prompted the assessment of drosophilid parasitoids for SWD control. Olfactometer bioassays with drosophilid parasitoids have shown that host substrate-related complex olfactory cues are relevant during host search. No information is available, however, on which fruit volatiles may be used as host-related cues. Here, we used gas chromatography coupled to electroantennography (GC-EAD) to evaluate the antennal detection of ecologically relevant fruit odours by two drosophillid parasitoids, Leptopilina boulardi (Hymenoptera: Figitidae) and Trichopria anastrephae (Hymenoptera: Diapriidae). We found that females of both wasp species are capable of detecting the main volatile compounds emitted by SWD-infested strawberries, five and ten days after oviposition by SWD females. The EAD-active fruit compounds were identified by GC-MS analysis as the common fruit esters ethyl butanoate, methyl hexanoate and ethyl hexanoate. The relative proportions of these fruit esters vary over time, with potential ecological significant for larval and pupal parasitoids. Our study is the first to report GC-EAD responses of microhymenopteran wasps of drosophilid flies. Understanding the sensory ecology of host-related chemical cues may be useful to optimize the biological control of D. suzukii by parasitoid wasps.