In ash trees, signs and symptoms of infestation by the emerald ash borer (Agrilus planipennis) include crown thinning and dieback, woodpecker damage, bark splits, eggs under bark, serpentine larval galleries, notched leaflets by adult feeding, D-shaped exit holes, and dead trees. High larval density eventually leads to tree death within two to four years after canopy thinning and branch dieback become evident. (Photo credit: Houping Liu, Ph.D., Pennsylvania Department of Conservation and Natural Resources)