By Joe Boggs, Amy Stone, and Dan Herms
EAB is a much smaller beetle, measuring around 10 to 13 mm (0.4 to 0.5 in.) in length. Adults have a flat back and round ‘belly’ when viewed head-on, which is the orientation of the beetle as it emerges from trees. Thus, EAB creates a characteristic ‘D-shaped’ emergence hole. Owing to the beetle’s small size, the holes are only around 4 to 5 mm (0.2 in.) across the flat side of the ‘D.’ The relatively small size of the exit holes makes finding them difficult until trees are heavily infested. Adding to the challenge is the tendency for the beetles to first infest the uppermost and outermost branches and then gradually work their way inward and downward with each successive generation. Consequently, exit holes are usually found at eye-level only when infested trees have been almost completely used by the beetles.
ALB is a large beetle, measuring around 25 to 40 mm (1 to 1.6 in.) in length. They have characteristically long antennae, with each one measuring as long as 40 to 50 mm (2 in.). The beetles produce large, round exit holes that can be almost 10 mm (0.4 in.) in diameter. Since the larvae feed deep within the xylem, the exit holes extend deep into the tree. Inserting a pencil into an exit hole is a good way to determine whether the hole was produced by a xylem-emerging borer. This is the so-called ‘pencil test.’ ALB does not appear to follow the same distribution pattern within a tree as EAB and exit holes are almost as likely to be found at eye-level as they are high in the tree’s canopy.
Read the full article: The Tale of Two Beetles