University of Vermont Extension 
Department of Plant and Soil Science

Anytime News Article

Dr. Leonard Perry, Extension Professor
University of Vermont
Japanese beetle, gypsy moth, and European corn borer are some of our more commonly known plant pests that have come from abroad.  Viburnum leaf beetle, Asian longhorned beetle, emerald ash borer, hemlock wooly adelgid, and the winter moth are some of our more recent introduced plant pests.  Dan Gilrein, entomologist for Cornell University on Long Island, provides some interesting facts about these insects and their damage.

Most of our introduced pests are the result of human activity, either purposeful or not.  If these seemingly harmless insects are not introduced for a particular purpose, only to escape, they more often hitchhike on wood and products in transit from other countries.  Wood boring insects, hiding in wood packing and crates on ships, are of special recent concern. 

The gypsy moth is an example of a purposeful introduction, brought to Medford, Massachusetts in 1869 by a French naturalist to try and establish a silkworm industry.  Some insects escaped, and within ten years it was obvious this pest was a problem.         

The Japanese beetle was first found in this country (New Jersey) in 1916, and has since spread throughout most of the eastern U.S. and Ontario.  The European corn borer was first found near Boston in 1917, perhaps entering the country the decade prior on broom corn shipments from Europe.   This pest attacks hundreds of plants, including ornamental plants, boring into and killing stems.  The linden tree, cut flowers, and dahlias are some it attacks.

More recently in 1947 the Viburnum leaf beetle appeared in Ontario from Europe, with breeding populations near Ottawa in 1978, and only reaching northeastern states this past decade.  It defoliates and kills several viburnum species, including some of our native ones important to natural settings and wildlife.  Other species are less susceptible, and are the ones to plant in landscapes if this pest is nearby.  A good listing of these species is provided by Cornell University (          

The Asian longhorned beetle accidentally arrived in cargo from Asia in 1996.  It is closely monitored around New York City and Chicago where it appeared, with quarantines and monitoring of plant shipments as well.  It could be a serious pest if it spreads, as it destroys hardwood trees.  Just around New York, control efforts have cost over $280 million, with over 8,000 trees destroyed since 1997 and almost 700,000 treated with insecticide.

The emerald ash borer is another recent pest being closely monitored in landscapes and the nursery trade.  This pest, too, accidentally arrived in cargo from Asia.  First seen in Detroit in 2002, it has since spread to surrounding states.  This is a deceptively attractive insect, as it kills ash trees—a valuable tree in urban landscapes and rural forests.  Since 2002 an estimated 20 million trees have been destroyed in the affected states.  If left uncontrolled, losses are estimated at $20-60 billion.

The hemlock wooly adelgid, once again, arrived in cargo from Asia.  First seen on the west coast in the 1920’s, it appeared on the east coast of the U.S. in Virginia in 1951.  Likely it was spread in infected landscape plants or wood.  Attacking mainly eastern species of hemlock, it has become a serious and rapidly spreading pest on the east coast where it has no natural enemies.  In its native Japan, it is kept in check by a native Japanese species of ladybug.  This pest can defoliate and kill a mature tree within four years, sometimes less.  It is destroying forest
ecosystems by killing off native hemlocks that provide a niche and many benefits for wildlife.

Winter moth is only recently coming to prominence, luckily, and is still somewhat localized.  First brought over from Europe, and found in Nova Scotia over 70 years ago, it has been in eastern Massachusetts for the last 10 to 15 years.  Early detection often was missed, as this insect is similar to and confused with a couple others.  Confirmation of its establishment in that area was finally made in 2003.  Natural enemies don’t seem to be controlling it, as it defoliates large areas around Boston feeding on many trees and shrubs.  The winter moth caterpillars can cause serious damage to apples and blueberries in particular, entering unopened buds.  Destroyed buds of course result in no blooms and so no fruit.

More on these and other invasive pests can be found through searches online, from state agriculture and extension agencies, or at websites such as of the Massachusetts Introduced Pests Outreach Project (  Visit these sites and study the photos, so you can identify these pests if you see them.  If you think you find one, check with one of these state agencies or your Extension Service plant diagnostic clinic.

If you visit an area known to have such invasive pests, resist the temptation to bring back trees and shrubs and accidentally the pest with them.  This is particularly true for plants you might dig from landscapes or get from friends. Susceptible plants often are quarantined from shipment within the industry from infested areas, so help support such prevention.

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