Eastern Forest Threat Center - Emerald Ash Borer

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Adult emerald ash borer

Adult emerald ash borer

David Cappaert, Michigan State University, Bugwood.org

Emerald Ash Borer
Agrilus planipennis

An exotic beetle from Asia identified as the emerald ash borer (EAB) was first discovered in July 2002 feeding on ash trees in southeastern Michigan, where more than 3000 square miles are now infested and more than 5 million ash trees are dead or dying from this pest.

Keywords: ash, Fraxinus species, beetle, Coleoptera, EAB, galleries, girdling, split bark, D-shaped exit holes, wilted foliage, thinning canopy

Distribution Map Distribution Source Image

Threat Description

Adults are slender, elongate, 7.5-13.5 mm long, and usually bronze or golden green overall, with darker, metallic, emerald green wing covers; they are generally larger and a brighter green than the native North American Agrilus species. Adult beetles feed on ash foliage, usually in small, irregularly-shaped patches along leaf margins. Females can lay at least 60-90 eggs during a lifetime, which are deposited individually in bark crevices. Larvae are white to cream-colored and reach a length of 26-32 mm. Larvae feed in the cambium between the bark and wood, producing galleries that eventually girdle and kill branches and entire trees. Bark may split vertically above larval feeding galleries. When a tree has been infested for at least one year, D-shaped exit holes left by emerging adults will be present on the branches and the trunk. Foliage wilts and the tree canopy becomes increasingly thin and sparse as branches die. Many trees appear to lose about 30-50% of the canopy after 2 years of infestation and often die within 3-4 years. Green, white, and black ash, as well as several horticultural varieties of ash have been killed by EAB.