Biological and ecological features of xylem-feeder vectors through establishment of a sustainable strategy for control of "Xylella fastidiosa"-vectors

Abstract

Xylella fastidiosa Wells et al., 1987, one of the most dangerous plant pathogenic bacteria worldwide, is disseminated by xylem-sap feeder insects. In Portugal, this pathogen was reported for the first time in January 2019 in Porto. However, in this country, knowledge of this community of insect vectors, potential vectors, and potential predators is still scarce. Thus, this thesis first studied the diversity and abundance of vectors and potential vectors in different Mediterranean agroecosystems. In vineyards, five xylem-sap feeders were identified, being Cicadella viridis (Linnaeus, 1758), the most abundant, followed by Philaenus spumarius (Linnaeus, 1758), Neophilaenus campestris (Fallén, 1805), Lepyronia coleoptrata (Linnaeus, 1758), and N. lineatus (Linnaeus, 1758). In almond, citrus, olive groves and adjacent scrubland, only two confirmed vectors of X. fastidiosa (P. spumarius and N. campestris) were recorded. The olfactory response of P. spumarius and C. viridis adults to different concentrations of cis-3-hexenyl acetate and cis-3-hexen-1-ol, volatiles frequently present in almond, olive, and vine leaves, was also studied. While P. spumarius females were significantly attracted at the lowest concentration, C. viridis did not show a significant preference for the volatiles at any concentration. In comparison to males, females of P. spumarius and C. viridis walked significantly at longer distances and at higher velocities. The olfactory response of P. spumarius, to five Portuguese olive cultivars, showed to be sex- and season-dependent. In Spring, females and males were significantly attracted to "Negrinha de Freixo"; while in autumn, females were significantly attracted to "Cobrançosa". With the aim to identify potential predators of confirmed vectors of X. fastidiosa, a polymerase chain reaction (PCR)-based approach was developed to detect DNA of P. spumarius in the spider's gut. Among the primers tested, one targeting the cytB gene was able to detect P. spumarius in the spider Xysticus acerbus Thorell, 1872, with high sensitivity, reaching 50% detection success 82 h after feeding. The feasibility of this primer set to detect predation of P. spumarius by spiders was confirmed in the field, where 20% of the collected spiders presented positive amplifications. Overall, the results obtained contributed to enhancing the scarce knowledge of the community of vectors and potential vectors of X. fastidiosa in several Portuguese agroecosystems. Moreover, insights into their olfactory behaviour and potential natural predators can help future implementation of approaches to manage the vectors and the spread of X. fastidiosa.