The emerald ash borer, Agrilus planipennis Fairmaire, a beetle native to Asia, was first detected in Michigan in 2002. Evidence suggests that the beetle was established in Michigan for years prior to its discovery. Emerald ash borer (EAB) has since been detected in many states, and also in Ontario and Quebec, Canada. In addition to spreading by natural means, EAB can be transported to new areas in infested firewood, timber, and nursery stock. This beetle has been responsible for the loss of millions of ash trees in North America.
In North America, EAB is known to infest all species of ash (Fraxinus spp.). Ash can be recognized by the presence of compound leaves which are arranged opposite of one another on the branches.
Eggs are laid between layers of bark and in bark crevices. Larvae hatch in about one week and bore into the tree where they feed on the inner bark and phloem, creating “S”-shaped galleries. Larvae go through four feeding stages, and then excavate a pupal chamber in the fall, where they will overwinter as prepupae. Pupation occurs in late spring, and adults begin to emerge through “D”-shaped exit holes in May and early June. Adults will remain active until the end of summer.
This commonly encountered beetle, the six-spotted green tiger beetle, Cicindela sexguttata, is often mistaken for EAB due to its similar appearance. It is a predator of small insects and is frequently found on hiking trails. There are other insects often mistaken for EAB.
New infestations are difficult to detect, as damage to the tree may not be apparent for up to three years. Symptoms of an infestation can include branch dieback in the upper crown, excessive epicormic branching on the tree trunk, and vertical bark splits. Woodpecker damage is sometimes apparent.
Ash may also be stressed by drought, diseases such as ash yellows, and by native woodboring insects like the redheaded ash borer, Neoclytus acuminatus (Fabricius) which creates a round emergence hole.
More information is available on the USDA website.