VOCs produced by healthy and Bactrocera oleae-infested olive fruits from three cultivars: impact on the host location behavior of the braconid parasitoid Psyttalia concolor

Olive aroma results from the emission of a wide range of volatile organic compounds (VOCs), which characterize the aromatic bouquets of olive oils. Genetic and environ-ment al factors play a key role on the chemical profile of fruits from different cultivar and/or from different geo-graphical areas. However, also biotic factors, as herbivo-rous damages, may activate plant indirect defenses trough the production of herbivorous-induced plant volatiles (HIPVs), peculiar molecules able to attract natural ene-mies. Psyttalia concolor is a larval pupal endoparasitoid, attacking a number of tephritid flies, including a major pest for olive groves, Bactrocera oleae. Here, we investigate the olfactory cues emitted by three olive varieties (cvs Arbequina, Frantoio and Leccino), to enlighten the stimuli involved in P. concolor host location. VOCs from B. oleae-infested and healthy fruits were identified by headspace solid-phase micro extraction (SPME) techniques and by gas chromatography-mass spectrometry (GC-MS). Significant differences for intra- cultivar emissions were evaluated using a general linear model, while inter-cultivar variations were examined by principal component and mul-tifactorial analysis. Indeed, in two-choice bioassays, parasi-toid females showed a strong preference in presence of olfactory cues from infested olives. GC-MS analyses showed qualitative and quantitative difference among vola-tiles emitted by infested and healthy olives. Furthermore, volatile emissions resulted to be peculiar for each cultivar examined, highlighting the strong impact of genetic on VOCs production. Two putative HIPVs were detected in infested fruits, regardless of the cultivar, the monoterpene (E)-ß- ocimene and the sesquiterpene (E-E)-a-farnesene. This study adds basic knowledge to the behavioral ecology of P. concolor, and identified VOC that may enhance inte-grated pest management programs in the field