Farm Fresh Perspectives: Exotic pest requires homeowner vigilance

In this day of widespread globalization and international trade, we see many benefits of collaboration and commerce with people and enterprises halfway around the world. However, this kind of global marketplace can result in problematic situations when living things from other parts of the world are transported into a new habitat. Whether that species ever presented a problem in its native land, when that species is moved, the new population may not be subject to the same kind of natural checks and balances it had originally. That is, if a species is introduced into an area without any predators, pathogens or parasites of that species, its population may explode and reach pest levels. Historically, this has happened numerous times. For instance, did you know the beloved Asian Lady Beetles that now inhabit every nook and cranny in our homes during cold weather were deliberately imported to North America by researchers hoping to control aphids on crops? Fortunately for us, they are simply a nuisance and cause minimal harm to people or property. However, some exotic invaders are not so innocuous…

The presence of the emerald ash borer has been confirmed in Kane County, Ill. This particular insect is native to Asia, and is purported to have been transported to North America in wooden packing materials in cargo vessels. This insect feeds solely on ash trees, and it was first discovered in southeastern Michigan in summer 2002. Since then, this insect has destroyed 12-20 million ash trees in Michigan, Ohio, Indiana and Ontario, Canada. Firewood transport from the affected states has been disallowed in an effort to curtail the spread of this pest, and aggressive eradication efforts are being undertaken. The U.S. Forest Service estimates 6 percent of trees in Illinois are ash trees and Illinois citizens are encouraged to be vigilant in monitoring their ash trees for this pest to avoid such a major loss in our own forest stands.

The adult form of the emerald ash borer, sometimes referred to as EAB, is a slender beetle, a half inch to three-quarters of an inch long, with bright, metallic green external coloration and purplish abdominal segments below the wings. Females lay their eggs on the bark of ash trees, and emerging larvae burrow under the bark to feed on the outer sapwood. The young form is a creamy white, legless larva with flattened, bell-shaped body segments and a pair of small appendages on the last segment. After several weeks of feeding, the larvae create galleries of curvy, S-shaped tunnels full of excrement in the inner bark that could become wide enough to girdle (kill by cutting off the flow of nutrients) a branch or even the trunk. When adult beetles emerge, they bore through the bark headfirst and leave an exit hole about the size of a BB (3-4 mm), that is round with one flat side; the hole is basically shaped like a capital letter D in any orientation.

Aside from seeing the larval or adult form of the insect itself, the S-shaped larval galleries under ash bark and small, D-shaped exit holes through the bark are good indicators of the presence of emerald ash borer. Other signs to watch for are: 1) die-back in the top third of the canopy of ash trees, which may progress to the rest of the canopy over several seasons; 2) new sprouts that grow from the roots and/or trunk of the affected ash tree, often with larger than normal leaves; and 3) increased woodpecker activity on the tree in question as the birds forage for EAB larvae under the bark.

Now, be aware there are a host of other tree pathogens and insect pests that may cause similar symptoms, so one must be very sure of the likelihood of an EAB infestation before getting the authorities involved.

First, make sure the tree under suspicion is an ash. The leaves will be compound leaves, formed of five to nine leaflets, and 8-12 inches long. The leaf margins may be finely toothed or smooth, depending on the variety of ash. Branches will be gray to brown, arranged directly opposite one another, and will NOT have a waxy coating that can be rubbed off like a boxelder (for help with ash identification, see the Michigan State University Extension’s publication at

Second, make sure the symptoms are not caused by another pest (like native ash borer or bronze birch borer) or disease (like ash anthracnose, verticillium wilt or ash yellows). After making double sure your ash has appropriate symptoms, contact a Certified Arborist (which can be located on the International Society of Arboritculture’s Web site at for an inspection, or your local Extension office for appropriate routing of your call. If your suspicions are confirmed by a professional, he or she will contact the Illinois Department of Agriculture for action.

For more information about emerald ash borer, consult the Illinois Department of Agriculture at, the Morton Arboretum at, the USDA Forest Service at, the Animal and Plant Health Inspection Service at or Please be diligent to help protect Illinois from the possibility of a major destruction of the ash tree population in our state.

Andy Larson works with the Initiative for the Development of Entrepreneurs in Agriculture in University of Illinois Extension. He can be reached at (815) 397-7714 or

From the June 21-27, 2006, issue

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