No evidence for cicadas' implication in Xylella fastidiosa epidemiology

Cicadas are prominent insects in the Mediterranean basin environments, including in olive orchards. The bacteriumXylella fastidiosa is a xylem-limited vector-borne plant pathogen that was introduced into southern Italy, causingsignificant losses of olive trees. Cicadas are xylem-sap feeders and potential vectors of X. fastidiosa; however, knowledgeof 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 transmitthe bacterium to healthy olives. In California, transmission was not achieved for the 19 grapevines caged each with agroup of two to three P. minor; moreover, none of the 19 insects (out of the 47 used for the transmission test) tested byculturing resulted positive for X. fastidiosa. In Italy, none of the olive recipient plants either caged with groups of threeC. orni individuals per plant confined in sleeve cages (55 plants) or placed inside a mesocosm with cicadas free to moveamong the recipient plants (30 plants), were infected with the bacterium. Moreover, out of the 314 field collected C. ornitested by qPCR, only 4 (1.27%) were positive for the bacterium. Our data suggest that the cicada species we tested likelyhave no or a negligible role in the natural spread of X. fastidiosa.