A REGIONAL-SCALE SCREENING OF FUNGI ASSOCIATED WITH XYLOSANDRUS COMPACTUS (COLEOPTERA CURCULIONIDAE SCOLYTINAE) INFESTATIONS ON BAY LAUREL IN ITALY

In 2020, surveys were carried out in different locations of Tuscany, Latium, and Sicily (Italy) to detect the presence of Xylosandrus compactus (Heichhoff) and to evaluate the fungal community associated with infestations by this invasive ambrosia beetle. In particular, we aimed to investigate the potential co-occurrence of phytopathogenic species that may pose a risk of spreading within the Mediterranean. Surveys were carried out in five localities where bay laurel (Laurus nobilis L.) plants showed signs of infestation by X. compactus. For the first time in Italy, in one of these surveyed localities, the ambrosia beetle was also consistently found attacking Rhamnus alaternus L., and samples from this host plant were included in the study. We were not interested in the already investigated nutritional mutualists consistently associated with the ambrosia beetle but focused on the potential occurrence of other fungal species inhabiting the body of adult beetles collected from infested galleries. Differences in fungal communities and/or variations in beetle-fungus species-specific associations among locations, as well as among the two host plants investigated are also highlighted. Thirty beetle adults were collected from each sampling site up to a total of 180 individuals including those from R. alaternus. In total, 31 different fungal genera were isolated. Fungal isolates belonging to the genera Geosmithia, Fusarium, Alternaria, Aureobasidium, Cladosporium, and Penicillium were shared by different regions. Differences in the fungal community composition, as well as in the occurrence of some isolated fungal genera, such as potential phytopathogenic ones (i.e., Fusarium, Geosmithia, Thyridium) and/or potential antagonists (i.e., Clonostachys, Aureobasidium, Trichoderma), alongside with opportunistic and/or commensals, were observed among sites and between the two hosts. Moreover, one entomopathogenic fungal species (i.e., Metarhizium brunneum) was found and isolated from beetle individuals infesting R. alaternus. The presence of X. compactus in the Mediterranean maquis of the Island of Elba is reported for the first time. Key Words: ambrosia beetle; black twig borer; Rhamnus alaternus; Geosmithia sp.; Laurus nobilis; Metarhizium sp.; fungal community.