Surveys on the distribution and parasitisation rate of Verrallia aucta (Diptera: Pipinculidae) on Xylella fastidiosa vectors in Apulia

Search for effective parassitoids of spittlebugs is one of the main objective of the research programs tackling the management of the epidemic of Xylella fastidiosa. Spittlebugs represent the main group of insect vectors in the outbreaks reported in the Mediterranean countries, with Philaenus spumarius (L.) being predominant in the epidemic of X. fastidiosa in olive trees in Apulia region (southern Italy). Current management of the vector populations include primarly weed management (tillage, mulching, application herbicides, pyroweeding) to reduce the juveniles' stages, and secondly chemical applications for adults. Although in Europe, during the past few years, surveys for natural enemies of spittlebugs have been intensified, very limited is the current knowledge on the potential biological control agents. Recent studies reported parasitization of field-collected spittlebugs with the endoparasitoid Verralia aucta Fallén in Northern Italy. In this work, we carried out surveys for the presence of V. aucta in different spittlebug adults collected in olive groves in the region of Apulia. From 2020 to 2022, a total of 43 locations covering the whole provinces, were monitored. A total of 2750 adults spittlebugs [P. spumarius (n. 1284); N.eophilaenus campestris (Fallén) (n. 1404); Philaenus italosignus Drosopoulos et Remane (n. 62)] were collected by sweep net and dissected under a stereomicroscope, to verify the presence of larvae of the pipinculide. The percentage of spittlebugs found to be parasitized was extremely variable among the three years and the species. None adults of P. spumarius collected in 2022 was parasitized, and very low-rate parasitisation (<5.5%) was recorded in 2020 and 2021. Conversely, N. campestris resulted more frequently parasitized, with parasitized specimens ranging from 4.8% (2021) to 23.5% (2022). Indeed, two larvae of V. aucta were found in adults of P. italosignus. DNA from seven representative fly larvae was amplified and sequenced using COI barcoding primers. All recovered sequences were compared with the sequences available in the databases GeneBank and BoldSystems, confirming the specificity with V. aucta. These data provide the first evidence on the presence of V. aucta in Apulia, suggesting that further investigations to esplore the potential role of this parasitoid in the framework of sustainable control strategy for vector populations of X. fastidiosa in olive grove. This work was carried out in the framework of the European projects XF-ACTORS (727987) and BeXyl "Beyond Xylella, Integrated Management Strategies for Mitigating Xylella fastidiosa impact in Europe ".