Despite its tiny size and its attractive shimmering color, this emerald-green beetle is a feared pest. The emerald ash borer, Agrilus planipennis, is about a half-inch long. It can be distinguished from green leafhoppers by its metallic color.

This emerald is no jewel

The ash borer is an invasive Asian insect that first appeared in the U.S. in 2002, when it was discovered in Michigan. It may have been around for as long as a decade before it was spotted. This pest's attacks on ash trees across the Midwest are predicted to cost billions of dollars in losses, and it has already caused the destruction of 20 million ash trees in Michigan alone.

In our region

On June 13, 2006, the Illinois Department of Agriculture confirmed a sighting of the beetle in Geneva, Illinois. It has since been spotted in other Illinois localities, including Homewood, Country Club Hills, Glenview, Hazelcrest, and Carol Stream.

Since this pest’s arrival in the U.S., forestry experts from local, state, and federal agencies have continued surveying ash trees in the region to determine the extent of infestation and to prevent its spread.

Like many other beetles, the emerald ash borer is a short-distance flier. Its main route of infestation is through the careless transporting of logs, branches, and firewood — and that’s probably the way it first reached North America. Because of this, many states prohibit carrying firewood across state lines and into parks for use in campfires. Various restrictions are in place in many of the Great Lakes States, where the beetle has already taken a toll on ash tree populations.

Infestation

In North America, the emerald ash borer attacks only ash trees. The female deposits eggs, one at a time, in bark and crevices on the sunny side of the tree. She may lay up to 90 eggs. The eggs hatch about a week later, and wormlike larvae burrow into the bark to reach the underlying phloem (food conducting tissues). Eventually the larvae attack sapwood, leaving curved tunnels reaching a foot in length. They winter over inside the tree, sometimes for two winters, and then they emerge as adults.

As the beetles exit the tree, they leave distinctive D-shaped holes — this is one of the primary signs of infestation. Thinning or yellowing leaves may also indicate infestation. Heavy damage by woodpeckers may occur as they feed on the beetles. And of course, watch for the distinctive adult beetle itself, crawling about on the sunny side of the tree.

Preventing an infestation

One of the best ways to protect your landscape from any kind of pest or disease is to have a variety of species, and to get the best quality nursery stock, selected for hardiness and resistance. Healthy, properly watered and maintained trees are always the most resistant to any kind of disease or infestation.

Treatment of ash trees with insecticides has not generally shown to be a wise method of prevention or removal of an emerald ash borer infestation (local and state agencies often require infested trees to be removed to prevent further spread).

If you use firewood, make sure it comes from a reputable local dealer, and inspect it for signs of infestation; firewood is a common cause of infestations by Asian longhorn beetles, sirex woodwasps, and gypsy moths, as well as being a carrier of beech bark disease.