No evidence for cicadas' implication in Xylella fastidiosa epidemiology

Cicadas are prominent insects in the Mediterranean basin environments, including in olive orchards. The bacterium Xylella fastidiosa is a xylem-limited vector-borne plant pathogen that was introduced into southern Italy, causing significant losses of olive trees. Cicadas are xylem-sap feeders and potential vectors of X. fastidiosa; however, knowledge of their role in the transmission of this bacterium is limited. We carried out two separate experiments: the first in California (USA), where we verified the capability of Platypedia minor to transmit X. fastidiosa from infected to healthy grapevines; the second in Apulia (South Italy), where we evaluated if Cicada orni collected on infected olive plants were able to transmit the bacterium to healthy olives. In California, transmission was not achieved for the 19 grapevines caged each with a group of two to three P. minor; moreover, none of the 19 insects (out of the 47 used for the transmission test) tested by culturing resulted positive for X. fastidiosa. In Italy, none of the olive recipient plants either caged with groups of three C. orni individuals per plant confined in sleeve cages (55 plants) or placed inside a mesocosm with cicadas free to move among the recipient plants (30 plants), were infected with the bacterium. Moreover, out of the 314 field collected C. orni tested by qPCR, only 4 (1.27%) were positive for the bacterium. Our data suggest that the cicada species we tested likely have no or a negligible role in the natural spread of X. fastidiosa.