The Asian ambrosia beetle Xylosandrus germanus (black stem borer, Coleoptera: Curculionidae) was introduced into the United States c. 1932. It occurs across much of eastern North America and parts of the Pacific Northwest, attacking a broad range of stressed, woody hosts including ornamental and orchard species. It is a cryptic wood-borer; the foundress tunnels into the sapwood of hosts where it cultures a symbiotic fungus as food for its offspring. Other ambrosia beetles have been shown to display cooperative brood care, a division of labor by siblings and an overlap in generations, but this has not been fully described for Xylosandrus spp. Using a novel artificial diet arena, we quantified the behaviors of X. germanus larvae and adults within galleries over 10 weeks. After initial inactivity waiting for the fungal gardens to establish, foundresses performed various tasks within the first 3 weeks such as digging the full gallery, cropping the fungal gardens, tending brood, and blocking the gallery entrance (the main behavior observed). Subsequently they appeared to only spend time blocking the entrance. Larvae were mainly observed to feed, crawl or be inactive within the gallery. Adult female offspring were primarily inactive, likely due to dormancy. Adult male offspring actively crawled and attempted to mate with their sisters before eventually dispersing out of the gallery. Cooperative hygienic behaviors (frass removal, cannibalism, grooming siblings) were observed but a division of labor among offspring was not obvious. No generational overlap occurs in X. germanus; thus, true sociality is not present.
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