Identify the Emerald Ash Borer

The larva or grub lives and feeds under the bark, and is the insect life stage that is solely responsible for tree damage. Adult beetles will feed on ash leaves, but do not cause noticeable damage. Larva damage the ability of the tree to transport water and nutrients, and may kill the tree in as little as 2 to four years.

Although more emerald ash borer locations are being found in Iowa, Iowa State University specialist encourage Iowa homeowners to evaluate their ash trees and to hold off on any insecticide prevention, unless they are within 15 miles of confirmed emerald ash borer infestations.

Tree symptoms are usually noticed toward the top of the tree first. Please visit our "What Are Ash Tree Symptoms ?" page for more information on what to expect in the host tree.


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1.) How to Identify the Larva or "Grub"

Distinct S-shaped or serpentine tunnels and galleries under the bark indicate EAB larva. Multiple galleries may run together with no discernable size and shape as more larvae are found infesting a tree.


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Larva have bell-shaped segments toward their posterior, and are slender with chewing mouth parts. These segment shapes indicate emerald ash borer larva. The larva reach approximately 1.25 inches in length before they pupate toward late fall and early spring.

2.) How to Identify the Adult Beetle

Beetles emerge from under the bark by chewing a D-shaped hole, usually June through late July with peak emergence expected in June. Emergence will gradually deminish through the summer months; however some late individuals may emerge late summer.


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The beetle is emerald green and shinny, and is about 1/2 inch long, and 1/8 inch wide. The abdomen under the wings is a bright shinny purple. The adult Emerald Ash Borer beetle will emerge or exit the tree by chewing a distinctive D-shaped hole through the bark approximately 1/8 inch wide. The exit holes may be orientated in any direction, top, bottom, or sideways.


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The D-shaped holes occur in the upper tree canopy first, making it very difficult for homeowners to spot. By the time D-shaped holes are noticed near ground level, the tree will likely be in severe decline.

3.) Insects That Are Often Mistaken for Emerald Ash Borer

People often confuse emerald ash borer with a number of common beetles and insects such as the tiger beetle, bronze birch borer, Japanese beetle, two-lined chestnut borer, caterpillar hunter, ash clearwinged borer, and redheaded ash borer just to name a few. Many of the native insect galleries that are found under the bark of trees are also confused with EAB.

The Iowa, Illinois, and Minnesota documents that you see on this page are available by clicking on the page links. These documents have pictures of the most commonly mistaken insects for emerald ash borer.


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