Xylella fastidiosa is a bacterial pathogen responsible for several serious plant diseases across the world such as Pierce disease within grapevine in California and Citrus Variegated Chlorosis in Brazil. In 2013 X. fastidiosa was detected in Europe, associated with Olive Quick Decline Syndrome in olive trees in Apulia, Southern Italy. Since, the presence of the bacterium has also been confirmed in France, Spain, and Portugal. Although the initial introduction of X. fastidiosa in Europe was through movement of infected plant material, the natural spread of the bacteria from plant to plant occurs via xylem feeding insects belonging to the Order Hemiptera. In the Americas, the primary vectors are the glassy-winged and blue-green sharpshooters of the Cicadellinae sub-family however within Europe, it is the common meadow spittlebug or froghopper Philaenus spumarius of the Aphrophoridae family that has been identified as the main vector . However, all sharpshooters and spittlebug species should be considered potential vectors of Xylella. Further research is required on the biology and population levels of other potential vectors and should include wherever possible transmission studies on the efficiency of any vector to transmit the bacterium to a range of relevant host plant species. For example, Cicadella viridis is the most common and wide-spread sharpshooter of the Cicadellinae sub-family in Europe requiring further study on its behaviour and nymphal stages. The movement of vectors between crops and wild plants is essential to understand the epidemiology of Xylella. Seasonal movement and abundance of vectors is well-studied in vineyards and citrus groves in the Americas and more recently within olive groves, however additional research into other agroecosystems would be of benefit. Routine surveillance for X. fastidiosa is carried out on symptomatic plants however it is also possible to detect the bacterium within the foregut of insects. Recent studies have indicated that, in conjunction with plant surveys, testing vectors for X. fastidiosa could be an important tool for monitoring the bacteria within the wider environment . Within vineyards, the collection and monitoring of sharpshooters is carried out using sticky traps, however collection of Philaenus is more labour intensive and in this context the development of traps or lures for known vectors should be investigated. Philaenus spumarius plays an important role in the transmission of X. fastidiosa and understanding the biology and behaviour of vectors and potential vectors is vital in preventing the introduction and spread of the disease; therefore, this project aims to improve our knowledge of both vectors and potential vectors of X. fastidiosa within differing habitats and climates. As well as sharing vector survey data from across the globe, studies on plant host preferences and vector movement between crops and wild plants were investigated. Different trapping techniques were discussed and reviews on potential biocontrol agents and natural enemies were considered. Transmission experiments on potential vector Aphrophora salicina were carried out; and endosymbiotic bacteria studies on vector populations were assessed.

Report of the Euphresco project 2020-F-341 'The insect vectors of Xylella fastidiosa (Xf vectors)'