Phagodeterrence as a strategy to curb vector activity and Xylella fastidiosa transmission

Reducing the frequency of insect vectors-plant interaction is crucial for minimizing the likelihood of vector borne plant pathogens transmission. The bacterium Xylella fastidiosa, whose the main vector species in Europe is the meadow spittlebug Philaenus spumarius, is threatening the agricultural heritage worldwide. Given the lack of curative methods, current X. fastidiosa control strategies focus on reducing the insect vectors abundance through ground cover removal and chemical treatments. However, this strategy does not seem to limit the bacterium spread besides causing side effects. Here, we explored whether vector activity and bacterium transmission could be curbed harnessing repellence and/or phagodeterrence induced by a plant-derived chemical compound causing no to marginal spittlebugs mortality. A Eucalyptus globulus extract (EGe) was selected as a model compound, due to its documented repellent/phagodeterrent activity against several insects’ taxa and low risk profile. First, using the Electrical Penetration Graph (EPG) technique, we assessed the effect of EGe on P. spumarius probing behaviour testing four routes of exposure i.e. delivery to the xylem by endotherapy, root drench, foliar spray, and insects’ topical exposure. The best results were obtained when the extract was directly injected into the xylem, making almost half of the spittlebugs leave the treated plant after ingestion. Further choice tests with non-infective insects and X. fastidiosa inoculation trials confirmed that the delivery to the xylem of a phagode terrent chemical affects vector activity. Our results prove that reducing host plant suitability for the vector, rather than just relying on insecticide-induced mortality, could therefore represent a sustainable strategy for containing X. fastidiosa spread.