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Emerald ash borer poses threat to trees in Illinois

Jim Barlow, Life Sciences Editor
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emerald ash borer
Photo by James E. Appleby, University of Illinois
The emerald ash borer is about one-half inch long and under bright light is dark green in color.

CHAMPAIGN, Ill. — A half-inch-long beetle known as the emerald ash borer, which is devastating ash trees in Michigan, poses a serious threat to Illinois, says an entomologist at the University of Illinois at Urbana-Champaign. Officials fear that beetle-infested firewood could be accidentally transported into the state.

"This is a very, very dangerous pest of ash trees," said James Appleby, a professor in the department of natural resources and environmental sciences and a scientist with the Illinois Natural History Survey. "Ash trees in the state already are in a state of decline from other factors, so it is important that people look for symptoms of an emerald ash borer infestation, which represents an additional and real threat. If these borers are out there, we need to find them so we can take action to contain them."

The emerald ash borer, Agrilus planipennis, a native of eastern Asia, was identified in the Detroit area a year ago and now 13 Michigan counties, as well as some areas of Ohio and Canada, are under quarantine to prevent the transportation of ash trees, branches, logs and firewood. Some 6 million trees in Michigan have died or are dying from infestation. Scientists believe the insect has been present for as many as 10 years, possibly introduced in ash wood used in shipping, Appleby said. The accidental movement of infested firewood could introduce the beetle to Illinois, he added.

The 178 million ash trees in Illinois represent about 9 percent of Illinois forestland. The total does not include trees in urban plantings or in nurseries. Drought, poor growing sites, lilac borers and native ash borers, and diseases, such as ash yellows, already are damaging many Illinois ash trees. All ash species are at risk from the new threat.

Signs of infestation, Appleby said, are D-shaped holes about one-eighth inch in diameter on large branches and trunks and numerous ash sprouts at the base of dead trees.

Adult emerald ash borers are commonly seen during sunny mid-summer days, feeding on leaves and crawling along branches and trunks of the trees. During June and July, they deposit eggs in the crevices of tree bark; about 10 days later, the larvae emerge and feed under the bark. Full-grown larvae, which are cream-colored and are about three-fourths of an inch long, spend the winter under the bark and in the sapwood.

Borer-infested trees may go undetected until symptoms such as upper tree canopy dieback occurs and the D-shaped emergence holes are seen on trunks and branches. Depending on tree size, symptoms may not show for a couple of years, Appleby said. In some trees a vertical bark split may occur on the trunk. If the bark is removed at such sites, S-shaped tunnels dug by the borer, known as serpentine larval galleries, can be exposed.

The emerald ash borer, Appleby said, easily can be confused with the brilliant green tiger beetle, a native insect often seen on the ground in open areas. The emerald ash borer can appear brown in the shade but is a dark green under bright daylight.

Appleby and colleagues Phil Nixon, also of the department of natural resources and environmental sciences at Illinois and the Natural History Survey, and Charles Helm, also of the Natural History Survey, have surveyed the damage in Michigan. They also have been working with Kenneth Kruse of the Plant Protection and Quarantine division of the U.S. Animal and Plant Health Inspection Service and Kathy Sharpe, an entomologist with the Illinois Department of Agriculture, on plans to deal with any infestation in Illinois.

Suspected sightings of emerald ash borer or related tree damage should be reported to any local Illinois Extension office or any local forestry office of the Illinois Department of Natural Resources.

More information about the emerald ash borer is available through a Web site devoted to the borer ( and maintained by the USDA Forest Service.