Xyleborinus saxesenii, commonly known as the fruit-tree pinhole borer, is a species of ambrosia beetle in the family Curculionidae.

[5] X. saxesenii inoculate the wood in which they inhabit with the fungus and farm it to utilize it as a food resource.

[6] X. saxesenii are a haplodiploid species that have a heavily biased sex ratio in favor of females.

[7] Males do not contribute much to the productivity of the nests, and typically spend a large amount of their time searching for mates.

[7] Unlike males, females contribute to gallery productivity and may even delay sexual dispersal to help with tasks such as brood care.

[2] X. saxesenii first originated in the Palaearctic region, but it has been introduced across the world, including North America.

[4] The introduction of X. saxesenii in the United States of America may have been due to transfer of wood which contained the species.

The Xyleborinus found in Uruguay are different from other American genera due to their cephalad conical scutellum and dense setae.

[4] The state of degradation of the dead wood may impact the humidity of the habitat, which can affect the ambrosia fungus with which the X. saxesenii has a symbiotic relationship.

In an experimental study varying the humidity of their habitat,[3] it was found that environments that are excessively dry (which would occur if a tree has been dead for a very long time) or humid (which would occur if a tree has just died) lead to reduced offspring fitness.

Both deviations from optimal humidity result in reduced ambrosia fungi success, which most likely caused a reduction of food resources that led to the lowered offspring fitness.

[14] After the fungal garden is created and sufficient, which is typically 4–51 days after the gallery was established, the females will then lay 5-15 eggs.

[14] Both the larvae and adult female offspring contribute to productivity of the gallery, but there is a division of labor within these tasks.

[15] The mutualistic relationship of X. saxesenii with its respective fungal species leads to the potential for the presence of several enemies.

X. saxesenii primarily share a mutualistic relationship with the R. sulfurea fungal species by farming the fungus within their galleries.

[6] One example is Aspergillus, which is a pathogenic fungal spore that commonly competes with R. sulfurea and is often found in X. saxesenii experiencing disease.

An experimental study[16] has shown that X. saxesenii are capable of detecting the presence of Aspergillus, and females as a result increase hygienic behaviors such as social grooming to reduce its effects.

[16] In the presence of Beauveria bassiana, an entomopathogen, adult females and larvae exhibit different behavioral responses.

Adult female X. saxesenii exhibit sexual dispersal during the summer and fall seasons.

[17] These findings suggest that the adult females may delay their dispersal in order to help the success of their natal colonies.

[17] These characteristics classify X. saxesenii as a species that exhibits cooperative breeding, which is a system in which individuals help care for offspring that are not their own.

[8] Additionally, there may be costs associated with leaving the natal gallery, such as a low success rate in creating a new nest.

[7] Dispersal is further supported in a separate study in which mature females were shown to help take care of fungi and the brood for at least 17 days.

[19] X. saxesenii differs from other similar Xyleborinus species because it has smaller and less pointed spines at the end of its elytra.

[20] Females of X. saxesenii can serve as a vector to carry and transmit the spores of fungi during dispersal.

In a Tennessee based study investigating ambrosia beetle control methods, X. saxesenii were found to attack live chestnut trees.