Emerald Ash Borer Background Information

Below is a brief background on the emerald ash borer. For more information visit the national emerald ash borer website. For more information specific to Iowa, see the ISU Extension EAB web site.

Earlier Horticulture and Home Pest News articles on EAB are on-line:

The emerald ash borer (EAB) is a small green metallic beetle about ½ inch long and 1/8 inch wide that causes ash trees to die when infested. Since the discovery in North America in 2002 near Detroit MI tens of millions of trees have been killed. The emerald ash borer is also established in Windsor, Ontario, was found in Ohio in 2003, northern Indiana in 2004, northern Illinois and Maryland in 2006, western Pennsylvania and West Virginia in 2007, and Wisconsin, Missouri and Virginia in 2008.

EAB destroys the ash tree by cutting the plumbing of the tree. First, the female lays eggs in crevices of the bark. The eggs hatch and larvae chew through the bark and start burrowing in the cambium layer of the tree just under the bark. As the larvae grow they eat through the active phloem and xylem of the ash tree effectively strangling the tree by depriving it of water and nutrients. Each female adult lays about 60-90 eggs (one at a time), so the infestation can progress rapidly once the beetle is established.

The larvae spend the winter beneath the bark and feed for a short time in early spring. The larvae pupate and emerge as new beetles in late May through August. Adults fly to the top of the ash tree and feed on the leaves. Approximately two weeks later the beetles mate and begin the egg laying process. If an ash tree is infested with EAB it will die within 2-4 years.

One of the reasons EAB has proliferated is because it is not native to North America, and its natural enemies (predators and parasitoids) did not accompany this exotic species from its homeland at the time of initial introduction. All ash (Fraxinus species) trees are susceptible to EAB, and EAB will infest any ash tree, but prefers damaged or stressed trees.

EAB was accidentally introduced into the United States, apparently in wooden crates carrying cargo from Asia. The first infestation was Detroit, Michigan in 2002. Researchers have determined, though, that the beetle has resided there for 10 or more years before it was finally discovered. Subsequent DNA testing has revealed that 3 distinct populations of EAB have been introduced into the USA. Since that time the borer has made its way (or has been moved by people) throughout Michigan, and to Ohio, Virginia, Maryland, Indiana, Pennsylvania, West Virginia, Illinois, Wisconsin, and Missouri. Although the borer is able to fly (estimates of 2 - 5 miles), it is moved long distances in infested logs, firewood and nursery stock.

The telltale symptoms that EAB has infested an ash tree are:

  • crown dieback
  • waterspouts from the trunk and major branches
  • D-shaped exit holes in the bark (1/8 inches in width). Photo below
  • S-shaped, frass-filled feeding paths under the bark
  • woodpecker holes
  • notching on the edges (only) of leaves

Although these signs can be helpful diagnostic tools, they are by no means fool proof. Some of these same signs can be made by native pests of ash trees.

The methods to control EAB have included:

  • quarantining infested areas to control the movement of ash wood and nursery stock out of those areas;
  • cutting down and destroying (chipping or burning) infested ash trees;
  • release of parasitoid wasps (biological control) in heavily infested states;
  • insecticide treatments, but results vary from 40-95% effectiveness .

Treatment of ash trees is not recommended until EAB has been positively identified 15 miles away. However, even if a tree has been treated, if eradication procedures are implemented the tree must still be cut down.

Feeding gallaries of emerald ash borer larva in Victoy, WI on April 9, 2009.  Photo by Laura Jesse.

Feeding gallaries of emerald ash borer larvae in Victory, WI on April 9, 2009. Photo by Laura Jesse.

Woodpecker damage to ash infested with emerald ash borer in Victory, Wisconsin on April 9, 2009.  Photo by Laura JesseWoodpecker damage to ash infested with emerald ash borer in Victory, Wisconsin on April 9, 2009. Photo by Laura Jesse


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on April 22, 2009. The information contained within may not be the most current and accurate depending on when it is accessed.