Dispersal of Philaenus spumarius, vector of Xylella fastidiosa, in olive grove and meadow agroecosystems

The spread of insect vectors is a key point in understanding the epidemiology of insect-borne plant diseases and in assessing effective vector control strategies. The transmission of the bacterium Xylella fastidiosa Wells in Europe is mainly due to spittlebugs (Hemiptera: Aphrophoridae). The meadow spittlebug Philaenus spumarius L. plays the major role in the spread of X. fastidiosa ssp. pauca ST53 on olives in the Apulia region (Italy). Despite its importance, little information is available on the mobility of P. spumarius. Dispersal capabilities of the meadow spittlebug were hence investigated by mark-release-recapture experiments. Several trials were carried out from May to October of 2016–2017 in two agroecosystems: olive grove and grass meadow, in the Apulia and the Piedmont regions (Italy), respectively. Adults of P. spumarius of both sexes were collected in natural grassland habitats, marked with an aqueous solution of albumin (10%) and then released at a single point in the centre of the experimental area. A total of ≈6500 and ≈3000 spittlebugs were release during Apulia and Piedmont experiments, respectively. Spittlebugs were recaptured through sweep net in fixed sampling points located up to a maximum of 250 m from release point. Recaptures were conducted every two or three days up to 17 days after the release. Marked insects were identified via an indirect ELISA. The dispersal capacity of P. spumarius adults was described estimating the probability density function describing the distribution of the end locations of insects relative to the source point (i.e. the dispersal kernel). Diffusion rates in the two agroecosystems were estimated under the hypothesis of a random walk and applying a Gaussian kernel. Spittlebugs were recaptured up to 155 meters and 200 m in Apulia and Piedmont, with 50% of total recaptures within 30 m and 40 m from release point, respectively. Results showed a high variability in the estimated median distance from the release point, ranging from 25 m (Apulia) to 35 m (Piedmont) per day, and from 356 m (Apulia) to 507 m for the estimated median of adult life-long dispersion. Estimated spread parameters of P. spumarius are fundamental information to model X. fastidiosa spread in Apulia and other European foci. Further researches are needed to investigate on influence of both vector’s physiology and environmental factors on movement tendency and directionality of P. spumarius.