XYLELLA FASTIDIOSA: VETTORI ACCERTATI E POTENZIALI IN AMERICA E IN EUROPA

The recent introduction of X. fastidiosa (Xf) in the Apulian Region of Italy, where it is associated with a severe dieback syndrome of olive trees, prompted research on the insect vectors of the bacterium in the new infected area. X. fastidiosa is a xylem-restricted bacterium transmitted by xylem-sap feeding insects. These latter belong to the order Hemiptera, families Cercopidae and Aphrophoridae (spittlebugs), Cicadidae and Tibicinidae (cicadas) and Cicadellidae (sharpshooters). The transmission of Xf by insects is peculiar in that it does not require a latent period, yet the bacteria are persistently transmitted. Bacteria are restricted to the alimentary canal and do not infect systemically the insect body. They adhere to and multiply in the pre-cibarium. Although Xf transmission is restricted to xylem-sap feeding insects, there is no species-specificity and all xylem-sap feeders should be considered potential vectors. Transmission efficiency varies substantially depending on insect species, host plant, and Xf genotype. The main vector species of Xf in North America, associated with the Pierce’s Disease of grapevine, and in South America, associated with Citrus Variegated Chlorosis, are listed. The potential insect vectors in Europe are discussed according to their reported presence by the Fauna Europaea database. So far, among the potential vector species, only the spittlebug Philaenus spumarius has been identified as a vector of the olive strain of Xf in Apulia. It is concluded that, while in Northern and Southern America sharpshooter vectors have been primarily associated with Xf epidemics, in Europe xylem-sap feeders other than sharpshooters might play a more important role in the spread of Xf.