Spittlebugs as vectors of Xylella fastidiosa in olive orchards in Italy

Abstract

The recent introduction of <i>Xylella fastidiosa</i> in Europe and its involvement in the Olive Quick Decline Syndrome (OQDS) in Apulia (Salento, Lecce district, South Italy) led us to investigate the biology and transmission ability of the meadow spittlebug, <i>Philaenus spumarius</i>, which was recently demonstrated to transmit <i>X. fastidiosa</i> to periwinkle plants. Four xylem-sap-feeding insect species were found within and bordering olive orchards across Salento during a survey carried out from October 2013 to December 2014: <i>P. spumarius</i> was the most abundant species on non-olive vegetation in olive orchards as well as on olive foliage and was the only species that consistently tested positive for the presence of <i>X. fastidiosa</i> using real-time PCR. <i>P. spumarius</i>, whose nymphs develop within spittle on weeds during the spring, are likely to move from weeds beneath olive trees to olive canopy during the dry period (May to October 2014). The first <i>X. fastidiosa</i>-infective <i>P. spumarius</i> were collected in May from olive canopy: all the individuals previously collected on weeds tested negative for the bacterium. Experiments demonstrated that <i>P. spumarius</i> transmitted <i>X. fastidiosa</i> from infected to uninfected olive plants. Moreover, <i>P. spumarius</i> acquired <i>X. fastidiosa</i> from several host plant species in the field, with the highest acquisition rate from olive, polygala and acacia. Scanning electron microscopy (SEM) revealed bacterial cells resembling <i>X. fastidiosa</i> in the foreguts of adult <i>P. spumarius</i>. The data presented here are essential to plan an effective IPM strategy and limit further spread of the fastidious bacterium.