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Emerald Ash Borer

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What is Emerald Ash Borer?


Emerald ash borer (EAB), Agrilus planipennis Fairmaire is a non-native pest that feasts on ash trees. It is a small, metallic-green beetle native to Asia.  Its larvae (the immature stage) burrow under the bark of ash trees, eating through the nutrient moving cambium layer, causing the trees to starve and eventually die.  While the beetle does not pose any direct risk to public health, it does threaten the tree population. Since the Emerald Ash Borer was first confirmed in the Midwest in the summer of 2002, hundreds of millions of ash trees have died.


Symptoms of EAB Infestation


Infestation of EAB can be difficult to detect until the branches of the tree start to die and/or bark of the tree starts to slough off. Usually, the leaves on the upper third of a tree will start to thin, and the branches will begin to die back. This is usually followed by a number of new shoots or branches sprouting along the trunk or at the base of the tree below the dead portions of the canopy. Additional evidence of infestation includes the tiny D-shaped exit holes on the branches and the trunk. Distinct S-shaped larval feeding tunnels may also be apparent under the bark. During the winter months, infested trees become apparent when woodpeckers begin to tear off small pieces of the bark as they try to feed on the larvae just underneath.  Unfortunately, once symptoms like this become very noticeable, it is difficult to save the tree from the damage done by the insect.


How do I know if my tree is an Ash?


Ash trees have several green leaflets per leaf stem, usually 7. The leaflets are located directly across from each other with one leaflet on the end. The leaf shape is “lanceolate,” which means they are much longer than wide, broader below the middle and tapering to the top.


What is the EAB’s lifecycle?


The Emerald Ash Borer adult is a dark metallic green beetle only about 1/2” in length and 1/8” in width. Adults are only present from mid-May to late June, when they feed on the leaves of ash trees. Soon after they emerge, the adults lay eggs on the trunk and branches of ash trees. After about a week the eggs hatch into larvae which then bore into the tree. It is this larval stage that does the major damage. Larvae are creamy white in color, can grow up to an inch long and are found under the bark of the trees. These larvae tunnel and feed, creating S-shaped galleries. This tunneling cuts off the food and water supply to the tree, causing it to die. Later in the year, the larvae pupate and overwinter under the bark. New adults emerge the following May. Their emergence holes are very small (only 1/8”) D-shaped holes and can occur just about anywhere throughout the tree.


For more information on Emerald Ash Borer, see:


USDA Pest Alert - Emerald Ash Borer