In 2002 the Emerald Ash Borer was first discovered near Detroit, probably arriving accidentally in the U.S. on packing material carried in cargo ships or airplanes arriving from Asia. As of June 2018 this woodboring beetle was found in 33 states (as far west as Colorado) and four eastern Canadian provinces. The adult beetle causes little damage when it nibbles on ash foliage, but its larvae (immature stage) feed on the inner bark of ash trees, thereby disrupting the trees ability to transport water and nutrients. Though the borer infests only stressed or dying ash trees in Asia, it attacks even healthy trees in the introduced areas in North America.
Male adult insects are bright metallic green, and the females are bonze colored. They’re about a half-inch long. The insect attacks only ash trees, and adults leave a D-shaped exit hold in the tree bark when they emerge in the spring. Woodpeckers like to eat the larvae, so heavy woodpecker damage on a tree may indicate larvae infestation. Borers can survive down to average temperatures of minus 22 degrees Fahrenheit, and larvae can survive heat up to 127 degrees Fahrenheit.
Since adult ash borers are able to fly about six miles, it makes control difficult. Soil applications, trunk injections, and trunk and foliage sprays are costly and not always effective. In Asia, the borer is attacked by several species of wasps that specialize in eating the insect’s larvae. Three species have been introduced into North America as biocontrol agents. Besides the introduced wasps, some native wasps have been shown to parasitize the borer. Research suggests that the native wasps help control the borer best in the initial phase of its invasion, and that the introduced wasps play a bigger role in control in the long run.
Ash trees provide food, thermal cover, nesting, and protection for a variety of wildlife species. But the Emerald Ash Borer has killed hundreds of millions of ash trees in North America, and it threatens to kill most of the 8.7 billion ash trees throughout North America. It is considered the most economically destructive non-native forest pest to invade the United States, surpassing even Dutch elm disease. The borers have cost municipalities, property owners, nurseries, and forest product industry operators billions of dollars. The insect continues to march westward. Ash trees are under siege, and its potential economic and ecological impact is enormous.
So, yes, we’re not done worrying about them yet.