Three-dimensional gallery system reconstruction reveals more frequent intraspecific than interspecific interactions in ambrosia beetles

Ambrosia beetle gallery systems are typically excavated into the xylem of host trees by a single mated female and are generally considered to function as independent units. However, field observations suggest that interactions among gallery systems may also occur. Using X-ray tomography to obtain three-dimensional reconstructions of ambrosia beetle galleries in flood-stressed and ethanol-injected trees, we found that intersections, where two or more galleries excavated by different females merge at one or more points, and intrusions, where a female begins excavating her gallery from within a gallery previously abandoned by another female of a larger species, are recurrent phenomena. We also observed that intraspecific intersections were generally more frequent than interspecific ones, regardless of tree treatment. These intraspecific intersections may represent a potential mechanism for cross-fertilization among the offspring of different founding females, thereby potentially increasing opportunities for outbreeding in these otherwise inbreeding species. Interspecific intersections, which could potentially facilitate lateral transfer of symbionts, occurred less frequently than expected, suggesting that ambrosia beetles may actively avoid such interactions. Overall, our study highlights that interactions among gallery systems may play a key role in shaping ambrosia beetle communities and their symbiotic networks, warranting further investigation.