Invasive Insects Threaten Massachusetts Forests

By Ken Gooch Gazette Contributing Writer

Most people think of cities and urban areas when they think of Massachusetts. Even though we’re a densely populated state, the Commonwealth is also the eighth most forested state in the country. Sixty-two percent—3,060,000 acres—of our land is covered by forest.

Most likely, people didn’t think much about the health of Massachusetts forests prior to the infestation and defoliation of trees by the gypsy moth in the early 1880s. The problem of invasive, non-native pests was not well understood at the time. Originally imported to Medford from Japan in an attempt to breed a hardy silk worm for the domestic textile industry, the gypsy moth was accidentally released into the environment and has since repeatedly defoliated millions of forested acres. Efforts to control this pest for more than a century have cost many millions of dollars.

In their native range, invasive species—whether insects, diseases or plants—live in balance with biological controls such as predators or pathogens. Introduced insects like the gypsy moth become problems because they have no natural enemies here to stem their reproduction and growth. They can easily assault and overwhelm trees native to our region.

Because of this, invasive species are an ongoing concern for forest health throughout the world. Here in Massachusetts, as well as elsewhere in the United States, many of these invaders have had severe ecological and economic impacts on our forests. While the gypsy moth population has declined in recent years, other imported species continue to raise concerns for the health of our forests. The following are some of the non-native insect threats that bear watching.

Hemlock woolly adelgid, a small aphid-type insect, was first detected in Massachusetts in the Forest Park section of Springfield in the late 1980s. The adelgid has been found primarily on Canadian hemlocks and is now fairly widespread in the state. Hemlock woolly adelgid hasn’t killed trees outright here as it has in areas to our south, but it has weakened many of our hemlocks to the point that the health of the trees has declined.

Winter moth was initially introduced to North America from Europe via Nova Scotia sometime prior to 1950. In that province it caused severe defoliation for many years before a predatory fly from its native range was released and provided effective control. However, winter moth remains a problem farther south: More than 70,000 acres were defoliated by the winter moth last year in Massachusetts alone.

In 2008, a full-scale insect eradication program was started when the Asian long-horned beetle was found in Worcester. This serious pest probably found its way to our state in wooden packing materials from Asia. The beetle attacks several important native tree species including maple, birch, willow and elm.

Authorities removed more than 20,000 infested trees in Worcester County to stop the spread of the insect. Federal and state agencies are now working to find the infestation boundaries, remove infested trees and replant areas where trees were removed in the eradication effort.

The emerald ash borer is not yet known to be in Massachusetts forests but has been found only 20 miles from our western border. Originally from Asia, it was first discovered in the U.S. in 2002, in the suburbs of Detroit. The borer has quickly spread to other states, including eastern New York State, spread primarily by people moving firewood from infested areas into previously unaffected areas. This pest has already killed many thousands of ash trees and has the potential to kill millions more. We will not be able to eradicate this insect pest from our environment, but with increased public awareness and use of biological controls such as predators and parasites, we should be able to slow the spread and possibly save the ash species in our state.

Our forests are at risk now more than ever due to these and other non-native species of insects, plants and diseases. Many tree insect or disease threats have been introduced through shipping ports in wood packaging materials. Some foreign insect and disease pests have come into our state through natural migration from other infested areas of the country—the hemlock woolly adelgid, for example, was probably brought in by migrating birds from infested hemlocks farther south.

Unfortunately, we’ll probably have to learn to live with many of the invasive species affecting our forests, although entomologists and forest health specialists have learned through the years that there are methods for controlling invasive pests. Scientists and forest managers are working to protect our forests by monitoring for these species and, when necessary or appropriate, applying biological control methods to protect our state’s valuable forest resources. Without constant vigilance and ongoing research, our forests could be very different places in the future.

Ken Gooch is the Forest Health Program Director for the Massachusetts Department of Conservation and Recreation.

Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 525 South Pleasant St., Amherst, appears every other week. For more information, call 413-256-6006, or write to us.

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