Behavioural response of the main vector of Xylella fastidiosa towards olive VOCs

The characterization of behavioural cues involved in the location of a host-plant by a phytophagous insect allows the elaboration of tools that can be exploited in the sustainable protection of cultivated plants. In this context, the identification of the blend of Volatile Organic Compounds (VOCs) released by a host plant can be profitably used for diverting pest insects away from it and towards specific targets (plants, traps). Philaenus spumarius, the main vector of Xylella fastidiosa, i.e., the pathogen bacterium responsible for the Olive Quick Decline Syndrome (OQDS), moves to olive trees when the grass cover dries up. To date, the possible role of chemical cues regulating this passage is not known. Moreover, it is still to be tested whether VOCs are involved in the resistance to the bacterium recorded in two olive varieties, namely FS-17 and Leccino. To verify these hypotheses, we characterized the behavioural response of P. spumarius towards the two resistant (Leccino, FS-17) and three common susceptible olive trees varieties (Ogliarola, Frantoio and Rotondella) in olfactometer bioassays. The response of P. spumarius towards olive varieties was sex-dependent: males were totally unresponsive whilst females were attracted by Ogliarola, Rotondella and Frantoio, and repelled by FS-17. No preference was recorded when testing females against Leccino and clean air. The characterization and the quantification of the VOCs released by the olive varieties tested supported the behavioural observations and paved the way to discuss their possible role in the elaboration of integrated protocols for the sustainable protection of olive trees from the deadly expansion of X. fastidiosa.