Abstract: Xylella fastidiosa (Xf) is a gram negative and xylem inhabiting bacterium that has been recently reported on olive trees associated with “olive quick decline syndrome” in Apulia region (south Italy). The spread of this bacterium at moment seems limited to the west coast of the Salento Peninsula (Lecce province) and has not yet been recorded in the rest of Italy and Europe. Due to the quick dissemination of Xylella fastidiosa, an effective approach is required for monitoring this bacterium in the symptomless areas surrounding the infection sites (buffer zone). Therefore, an evaluation of the possibility to utilize the Xf-positive insects (spy insect) as indicators of the presence of this vector-borne bacterium in apparently uncontaminated areas (e.g. in the buffer zones) was carried out. From May to June 2014, insects were collected from a restricted Xf-outbreak at Trepuzzi (in Lecce province), and from the area surrounding it (buffer zone). The study focused on species in the Auchenorrhyncha, a group that includes known vectors of Xylella fastidiosa. The bacterium was successfully detected by PCR in 3 out of 6 species of Auchenorrhyncha captured in the buffer zone, i.e. Philaenus spumarius, Neophilaenus campestris and Euscelis lineolatus. Infected adults of these species were detected throughout the buffer zone up to a distance of 1 km far from the infection site, thus confirming their important role as “spy insects” to early reveal the presence of the pathogen in apparently free areas before symptoms become visible on the plants.