Simulated flood-stress and X-ray tomography unveil susceptibility of different tree taxa to ambrosia beetles

Climate change will lead to higher frequencies of natural disasters, including flooding events. Consequently, more severe and widespread attacks by invasive ambrosia beetles associated with stressed trees are predicted to occur. In this scenario, understanding which tree species are expected to be more susceptible, as well as which ambrosia beetle species could be expected to have the biggest impacts, represent a research priority. To this aim, potted-trees of eight tree species (four in the order Fagales and four in the order Rosales) were first exposed to flood-stress in a common garden experiment; then emerging insects were counted and logs obtained from infested trees were analyzed through X-ray tomography to evaluate host selection patterns (entry holes), colonization success (percentage of branched galleries and offspring production), and potential damage to the tree (volume of the log occupied by galleries) by native and exotic ambrosia beetle species. Four ambrosia beetle species attacked flood-stressed trees: the native Anisandrus dispar and Xyleborinus saxesenii, and the exotic Xylosandrus crassiusculus and Xylosandrus germanus. Flood-stressed Rosales species were consistently more attacked than Fagales species, with different ambrosia beetle species showing distinct preferences for certain tree species. Rosales were also generally more suitable for ambrosia beetle reproduction than Fagales, even though differences were also evident among tree species within the two orders. The exotic X. crassiusculus was the most successful species, showing higher percentage of branched galleries and higher offspring production. Our study showed a differential susceptibility of common tree species to native and exotic ambrosia beetles in a flood-stress scenario. In addition, it highlighted that X-ray tomography provides a novel method for characterizing the host selection and colonization of trees by ambrosia beetles and can be considered a reliable methodology to improve our comprehension of these mechanisms.