In-gallery social behaviors of the ambrosia beetle Xylosandrus germanus (Coleoptera: Curculionidae)

Authors: Milbrath, Lindsey; Biazzo, Jeromy; MUDRAK, ERIKA - Cornell University

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2024
Publication Date: 1/20/2024
Citation: Milbrath, L.R., Biazzo, J., Mudrak, E. 2024. In-gallery social behaviors of the ambrosia beetle Xylosandrus germanus (Coleoptera: Curculionidae). Environmental Entomology. 53(1):85-93. https://doi.org/10.1093/ee/nvae003.
DOI: https://doi.org/10.1093/ee/nvae003

Interpretive Summary: The ambrosia beetle Xylosandrus germanus (black stem borer) is an introduced pest of ornamental and orchard trees. It bores tunnels or galleries into the sapwood of stressed trees where it grows a fungus to feed its offspring, and this is associated with tree decline and death. A few other species of ambrosia beetles display cooperative social behaviors inside their galleries. If these social behaviors could be disrupted, presumably this could cause beetle colonies to fail. We used a novel arena with an artificial diet to document the behaviors of the founding female (foundress) and offspring. Foundresses constructed the galleries and initially tended the fungal gardens and brood, but eventually they spent almost all their time blocking the gallery entrance. In contrast, her offspring helped to varying degrees with keeping the gallery and each other clean. Some cooperative social behaviors exist in the black stem borer, which may open opportunities for management of this and related pest species.

Technical Abstract: The east Asian ambrosia beetle Xylosandrus germanus (Blanford) was first detected in the United States in 1932. It now occurs across much of eastern North America and parts of the Pacific Northwest. It attacks a broad range of stressed, woody hosts including ornamental and orchard species. The foundress tunnels into the sapwood of hosts where it cultures a symbiotic fungus as food for its offspring. A few other ambrosia beetles have been shown to possess a facultatively eusocial structure among gallery members, but this has not been described for Xylosandrus spp. Using a novel artificial diet arena, we quantified the behaviors of X. germanus larvae and adults (foundress and mature offspring) over 10 weeks insider their galleries. Foundresses were solely responsible for constructing the gallery. They initially tended the fungal garden and brood but eventually spent most of their time blocking the gallery entrance. Larvae were mainly observed to feed, crawl or be inactive within the gallery, regardless of the absence or presence of adult siblings. 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 (removal of frass, cannibalism of dead nest mates, grooming siblings) were observed but a division of labor among offspring was not clear. Rather, foundress behaviors were mostly distinct from offspring behaviors, particularly as the gallery aged. Because no overlap in generations occurred, X. germanus displays a quasisocial structure.