Effect of the host plant on the life history, behaviour and fungal community of a fungus‐farming ambrosia beetle

Although there are benefits to being a generalist, the majority of herbivorous insects are diet specialists. This raises the question whether the ability to reproduce on various host plants hides an unknown ecological optimum. Our study investigated the existence of such an ecological optimum in the fungus‐farming ambrosia beetle, Xyleborinus saxesenii Ratzeburg (Coleoptera: Curculionidae). We hypothesised that X. saxesenii may exhibit higher fitness in specific hosts that are particularly abundant in their respective regions. To test this hypothesis, we bred X. saxesenii from a broadleaved forest population in semi‐artificial media mimicking either a coniferous or a broadleaved host‐tree species. As trade‐offs between different traits can occur, we examined various aspects of the life history, social behaviour and fungal symbionts of X. saxesenii. We found that dispersing females did not exhibit any preference, and that the host tree did not have any impact on life history parameters or larval and adult behaviours. The fungal community associated with the species was made up of identical fungal species, albeit with different relative abundances between host trees. Our findings indicate that X. saxesenii does not exhibit a specific adaptation to the most abundant host trees in its native habitat. However, we identified significant effects of laboratory breeding on life history traits, social behaviour and adult dispersal. This generalism in host use in combination with inbreeding mating system may be the main drivers of the invasion success of the Eurasian X. saxesenii, which is currently among the most prevalent and widely distributed ambrosia beetle species worldwide. We analysed the life history, behaviour and symbionts of Xyleborinus saxesenii in different host trees. The life history traits, behaviour and nutritional symbionts were not impacted by the host tree, but other fungal symbionts were. Our results show that wood‐dwelling insects do not always adapt to the locally abundant plants.