Targeting Xylella fastidiosa: sustainable management of Philaenus spumarius using carlina oxide

Xylella fastidiosa Wells, a bacterial plant pathogen, represents a threat to many crops all around the word. Unfortunately, no effective treatments are available to reduce the infection and, to date, the most promising strategy relies on controlling the meadow spittlebug Philaenus spumarius L. one of the main vectors of X. fastidiosa. Among insecticides and repellents, botanical insecticides represent valuable candidates. Their encapsulation into stable formulations, like nanoemulsions (NEs), can boosts the efficacy and stability. We investigated the toxicity, repellent, and antifeedant activity of carlina oxide, a polyacetylene isolated from the roots of Carlina acaulis L. (Asteraceae), and its NEs, against P. spumarius adults. In addition, we carried out electroantennographic (EAG) tests to evaluate the capability of the male and female antennae to perceive carlina oxide. EAG assays demonstrated that P. spumarius antennal olfactory system of both sexes is capable of perceiving carlina oxide over a wide range of doses and that females, at the lowest doses, have significantly greater olfactory sensitivity than males (0.01 and 0.1 µg, respectively (p < 0.001)). In toxicity experiments, the percentage of adult survival in topical and fumigant trials was high, while it resulted significantly lower in ingestion trials. In olfactory tests, P. spumarius showed a slight preference for green beans treated with 1 % carlina oxide. However, no significant differences were observed between treatments when the concentration of carlina oxide was increased to 3 %. On the contrary, feeding tests showed a significant repellent effect of carlina oxide against P. spumarius adults up to 24 h after the treatment and a reduction in P. spumarius presence on treated green beans ranging from 51.2 % to 94.7 %, if compared with control green beans. Overall, this study sheds light on the possible development of effective and environmentally friendly formulations of carlina oxide to manage P. spumarius. Further studies are needed to evaluate the efficacy of this natural compound in field conditions, and to investigate its potential side effects on non-target species.