Seasonal changes in population structure of the ambrosia beetleXylosandrus compactusand its associated fungi in a southern Mediterranean environment

Exotic ambrosia beetles are increasing in Europe due to global trade and global warming. Among these xylomycetophagous insects,Xylosandrus compactus(Eichhoff) (Coleoptera: Curculionidae) is a serious threat for several Mediterranean host plants. Carob trees growing in Sicily (Italy) have been extensively attacked by beetles leading to rapid tree decline. AlthoughX.compactushas been found in Europe for several years, most aspects of its ecology are still unknown. We thus studied the population structure and dynamics ofX.compactus, together with its twig size preference during a sampling of infested carob trees in south east Sicily. In addition, fungi associated with insects or galleries were isolated and characterized. The results showed that, in this newly-colonized environment and host plant, adultX.compactusoverwinters inside twigs and starts to fly and reproduce in mid spring, completing five generations before overwintering in late fall. The mean diameter of carob twigs infested by the beetle varied significantly over the seasons, with the insect tending to infest larger twigs as season progresses. The mean number of adults/gallery was 19.21, ranging from 6 to 28. The minimum temperature significantly affected the overwintering adult mortality.Ambrosiella xyleboriandFusarium solaniwere the main symbionts associated with the pest in this study.Acremoniumsp. was instead recorded for the first time in Europe insideX.compactusgalleries. Several other fungi species were also found for the first time in association withX.compactus. Our findings provide useful insights into the sustainable management of this noxious pest.