Invasive insect poses unprecedented threat to urban forests

In 2002, a green, jewel-like beetle was discovered in southeastern Michigan. Only a half-inch in length, this nonnative insect has proven to be invasive, killing hundreds of millions of ash trees across the United States.

Today, the United States Department of Agriculture (USDA) calls the emerald ash borer “the most destructive invasive forest insect ever to have invaded North America” and some estimate that the beetle could do $20 to $60 billion dollars in damage if left unchecked. The emerald ash borer has been reported in 35 states across the country, including all six Chesapeake Bay watershed states and Washington D.C.

While no one is certain how this invasive species entered the United States, it is likely that the beetle arrived on wood packing material from its native Asia. The emerald ash borer is well-suited to our climate and to our abundance of ash trees, which is one of the most common landscaping trees in the country.

The emerald ash borer lays its eggs in the cracks of ash trees. The larvae feed on the trees’ nutrient-rich bark and disrupt the trees’ ability to move food and water from its roots to its leaves. Ash trees typically lose most of their canopy within two years of infestation and die within three to four years.

Slowing the spread of emerald ash borer

While it seems unlikely that emerald ash borers will ever be completely eradicated, there are ways to fight back against this invasive insect. Insecticide injections into the trunks of healthy trees are highly effective in deterring infestation by these dangerous pests for two to five years. Additionally, the USDA has begun research into biological controls that can be useful long-term in fighting back against these insects. By introducing natural, non-native predators to the emerald ash borer, such as parasitoid wasps, researchers hope to disrupt the insect’s natural life cycle and control its spread. These newly introduced predators attack only a very narrow range of insects and would likely have no negative effects on the ecosystem.

The best thing anyone can do to slow down these destructive insects is to closely monitor the ash trees near them. To help prevent further infestations, people who live in and travel through known infested areas can do the following:

• Buy firewood where you burn it. Hauling firewood is the most common way emerald ash borers are moved from one area to another. By only burning locally sourced firewood, you can ensure that you are not contributing to their spread.
• Familiarize yourself with quarantine information. Learn your state’s guidelines for handling emerald ash borers.
• Do not plant ash trees. As the emerald ash borer is expanding its range across the country, planting alternative tree species is recommended for residential landscaping.
• Learn the symptoms of infestation. Monitor your ash trees and look out for symptoms of emerald ash borer throughout the year. Keep an eye out for the D-shaped exit holes that the beetles leave in the bark. Woodpeckers love to eat emerald ash borer larvae, and heavy woodpecker damage on ash trees may also be a sign of infestation.
• Learn about treatment options. If you believe you have an emerald ash borer infestation and are not sure what to do next, check out this decision making guide for managing an infestation.

Contact your county office or your state’s Department of Agriculture office with any questions you have about how to manage an emerald ash borer infection. You may also contact the USDA Emerald Ash Borer Hotline at (866) 322-4512.