Volatiles emitted by resistance inducer-treated grapevines affect Hyalesthes obsoletus behavioural responses

The planthopper Hyalesthes obsoletus Signoret (Hemiptera Cixiidae) is the main vector of ‘Candidatus Phytoplasma solani’, that cause the grapevine Bois noir disease. Amongst the alternatives to synthetic pesticides, many studies have investigated the use of resistance inducers to control plant pathogens and phytophagous insects. In this study, the planthopper behavioural responses to volatiles emitted by grapevine shoots treated with three commercial chemical elicitors were investigated in a dual-choice olfac- tometer. Each formulation was applied at one of three different times, as 0, 2, and 7 days before the bioassays. Insect behavioural responses toward grapevine volatiles differed significantly across formulations and application times. In particular, H. obsoletus were significantly (χ2 = 7.258, df = 1, P = 0.005) repelled by volatiles emitted by grapevines sprayed with a benzothiadiazole- based formulation 7 days before the bioassays. The two other formulations were based on oligosaccharides and glutathione and gave contrasting results. The planthoppers were significantly (χ2 = 3.571, df =1, P = 0.044) attracted to volatiles emitted by grape- vines treated with one of these formulations on the same day of bioassays, but not subsequently. This suggested a response to the product rather than an elicited response from the plants, so we conducted headspace analysis on samples of the three products to identify differences in volatile constituents for future experimentation. The remaining formulation had no effect at any of the post- treatment intervals. Our results indicate that the benzothiadiazole-based formulation may contribute to a novel sustainable inte- grated management strategy for the control of H. obsoletus, the main vector of the Bois noir phytoplasma.