In early May, adults emerge and move to small branches of stressed ash trees to seek egg-laying sites. After mating, females tunnel into the sapwood to deposit eggs in galleries that encircle the branch. After hatching, the larvae tunnel away from the main gallery. The larvae are white, legless, have a brown head, and are 2 to 4 mm in length. New adults emerge and feed before seeking hibernation sites in September and October.
Galleries constructed by the female often encircle a branch.
Leaves will often wilt and turn bright yellow from the gallery outward. An egg gallery can be identified by a row of ventilation holes about 1 mm in diameter and 5 mm apart in the bark. The area around the egg gallery is discolored and sunken, especially late in the growing season. The Western ash bark beetle generally infests only weakened or stressed trees, causing minimal damage. When many trees are stressed, bark beetle populations can increase rapidly and cause significant damage.