University of Vermont Extension
Department of Plant and Soil Science
Dr. Leonard Perry, Extension Professor
University of Vermont
The Asian longhorned beetle, the
hemlock wooly adelgid, and the emerald ash borer are three serious tree
threatening or destroying many hardwood trees in North America.
Learn what they
are, watch for them, and if you suspect these insects then report them
state entomology lab for positive identification
The Asian longhorned beetle is aptly
named as it has very long black and white banded antennae. Adult
beetles are large, about an inch to
inch and a half long, glossy black with white spots. It shouldn't
be confused with the
whitespotted sawyer, the cottonwood borer, or the locust borer, nor
confused with that of the sapsucker. The
larvae that live deep in the wood, boring and disrupting flow of water
nutrients, cause trees to die.
This beetle first was discovered in
this country in 1996 on several hardwood trees in Brooklyn, New
Since then, beetles have been discovered in
other locations near there, New Jersey, Chicago, and most recently in
August 2008 in Worcester, Massachusetts. The beetles were
have entered the
country in wood pallets and packing material on shipments from
more by natural means, they can be spread through moving firewood or
from infested areas.
What makes this beetle such a threat
is that it attacks many hardwood trees, including maples, birch,
ash, poplar, willow, mountain ash, and elms.
If it becomes established in this country it could cause more damage to
trees than Dutch elm disease, chestnut blight, and gypsy moths
combined. It could destroy millions of acres of
American hardwoods, threatening industries such as maple, timber, and
tourism. Controls consist of both
chemicals applied by professionals, and removing all potential host
trees up to
a half-mile from infested trees.
The hemlock woolly adelgid is an
aphid-like insect, barely detectable to the eye, which lives at the
hemlock needles. Sucking the sap from
the needles, it causes them to turn color, die, and fall off.
What you should look for is the white,
cottony masses at the needle bases that cover the insect, most
late spring. All these adelgids are female and can lay up to 300 eggs,
resulting in up to 90,000 new adelgids in one year.
The hemlock woolly adelgid is
another introduced or "exotic" pest, native to Asia
where it is not a problem. It was
introduced to this country in the 1920's in the Pacific Northwest, and
early 1950's to the Virginia
area. It lacks natural enemies in America, so has spread from
Georgia to Maine
on Carolina and
Eastern hemlocks. Since 2002 it has been
killing trees in the Smoky Mountains National Park. In Virginia's
Shenandoah National Park, 80 percent
of the hemlocks have been killed.
This adelgid spreads naturally by
birds and mammals, and also by humans such as in infested nursery
stock. There are quarantines on selling hemlocks
from infested areas, so make sure you don't bring hemlocks from such
your own. Controls include injections of
pesticides into infested plants, insecticidal oils and soaps, and
controls that are being developed.
The emerald ash borer is a pretty
beetle, dark metallic green, one half inch long and one- eighth inch
wide. Larvae spend the summer and fall tunneling
under outer tree bark, disrupting sap flow. This can cause a tree
to die in only two to
three years. The larvae overwinter, then
adults emerge from mid-May through June, only to lay eggs and start the
Symptoms of injury include an
initial thinning of foliage and crown dieback, larval tunnels under the
woodpecker injury as they seek the larvae, and the D-shaped exit holes
tunnels. Controls are not yet feasible
in the wild, but in landscapes include pesticides applied by
professionals. Firewood should not be
moved from infested areas as this is a major means of spread.
Only ash trees are attacked, but all
16 native species of ash are susceptible.
This is another invasive pest, believed to have entered the U.S. on
wood shipping materials from Asia. It was first
identified in the Detroit area in 2002, and has
spread since then to several other Midwestern and Mid-Atlantic states,
Ontario and Quebec.
With ash a major landscape tree, and
valuable in timber and many wood products, a national outbreak could
billion in losses. Already this pest has
killed tens of millions of trees in southeast Michigan alone, and
similar numbers in other
states, resulting in tens of millions of dollars in losses.
More information on these pests can
be found online such as from the northeastern area US Forest Service
(www.na.fs.fed.us/fhp/). Check on this and other websites for lists and
areas where these pests currently exist in order to avoid unknowingly
them through firewood and plants.