The emerald ash borer is a shiny emerald green beetle that kills living ash trees. Emerald ash borer is considered an invasive species in Canada. In Canada, beginning in late May and early June adults of the emerald ash borer emerge by chewing out through the bark of the host tree, creating a characteristic D-shaped hole. Females lay their eggs in bark crevices or under bark scales on the branches and trunks of the host trees. Newly hatched larva tunnels out the bottom of the egg, down through the layers of the bark until it reaches the interface between the bark and the wood. Adults feed on the edges of the foliage, but it is the feeding of the larvae between the bark and sapwood which results in ash tree mortality. Signs and symptoms of attack include crown dieback, bark deformities, woodpecker feeding holes, D-shaped emergence holes and shoots growing out of the trunk, roots and branches of the trees. Signs and symptoms of attack are not obvious until populations of the beetle are well established.
More information (PDF)