Keyhole Ambrosia Beetle

Xyleborinus saxesenii, commonly known as the fruit-tree pinhole borer, is a species of ambrosia beetle in the family Curculionidae. It is native to the Palaearctic region but has been introduced in many locations, including North America. X. saxesenii typically live in freshly dead wood, but it has also been reported to attack live trees. Such attacks on live trees may lead to economic damage.

Like other ambrosia beetles, Xyleborinus saxesenii has a symbiotic relationship with ambrosia fungi, particularly the Raffaelea sulfurea species. X. saxesenii inoculate the wood in which they inhabit with the fungus and farm it to utilize it as a food resource. Although there are benefits to farming fungi, there are also costs in the form of microbes and pathogens that infiltrate these fungal farms.

Xyleborinus saxesenii are a haplodiploid species that have a heavily biased sex ratio in favor of females. Males do not contribute much to the productivity of the nests, and typically spend a large amount of their time searching for mates. Unlike males, females contribute to gallery productivity and may even delay sexual dispersal to help with tasks such as brood care. Both adult females and larvae contribute to tasks within the gallery, but there is often an age-based division of labor in these tasks.