The two spotted oak buprestid (Agrilus biguttatus) beetle is difficult to observe on oak trees because the adults feed and mate up in the canopy, and the larvae develop beneath the bark. The adult beetles lay eggs in the bark crevices of declining trees and the newly hatched larvae tunnel through the corky outer bark to feed on the nutritious inner bark and cambium, creating long, sinuous galleries.
Damage to trees occurs through larval feeding. When the number of larvae is high, the galleries may act to restrict the flow of nutrients within the tree, reducing its health. This “girdling” effect has been implicated in tree mortality, although if the number of larvae are low, trees can recover, producing callus tissue to cover over galleries. Mature larvae eventually pupate in the outer bark plates, before the adults emerge, creating the characteristic “D” shaped exit holes.