Hemlocks fall victim to bug on the move Parasitic adelgids draw the life from stately eastern forests


Inexorably, tiny parasitic insects from Asia called woolly adelgids are punching deeply and destructively into the hemlock forests of the Eastern United States.

Traveling about 30 miles a year or even faster lately, they have fanned out from Virginia to invade the hemlocks' heartland in northern New England and march down the Blue Ridge into North Carolina and westward into West Virginia.

The adelgids advertise their presence on hemlock needles by depositing strings of little white egg sacs that look like artificial snow on a Christmas tree. And wherever they go, they eventually suck the life out of hemlocks and leave behind bare, gray skeletons.

A natural enemy

Now the first battalions of what experts hope will become an army of the adelgid's natural enemies - previously unknown black ladybug beetles the size of poppy seeds - are coming to the rescue.

Scientists who discovered the adelgid-eating ladybugs by literally beating the bushes (actually, the branches of Japanese hemlocks) have reared thousands of them in the laboratory and released them experimentally in the wilds of Virginia and Connecticut. There the beetles have reduced adelgid populations by 47 percent to 100 percent. Just as important, the ladybugs have become established in the forest.

Can they save the hemlocks?

"So far, things are looking very encouraging," said Dr. Mark McClure of Valley Laboratory, the Connecticut Agricultural Experiment Station in Windsor, who in the 1980s first raised the alarm about hemlocks and adelgids. It might be possible in a year or so to expand the experimental control program into a fully operational one, he said.

The adelgid does its damage by piercing the tissues of a hemlock and sucking out the tree's juices, gradually reducing its foliage and in time starving it.

Adelgids attack a tree by the hundreds of thousands and can kill it in a year, and almost invariably do so within four.

No one knows how the adelgid got to the United States, but it is believed to have come from Japan. It appeared first in the Pacific Northwest, but hemlocks there resisted the insect.

In the East, it turned up around Richmond, Va., in the 1950s and spread into New Jersey, Pennsylvania, lower New York and Connecticut. The insect also attacks ornamental hemlocks, which can be protected from adelgids by insecticides.

The adelgids have eaten their way north through west-central Massachusetts and are on the Vermont and New Hampshire borders. Immediately ahead lie larger and more continuous stands of hemlocks, and the adelgid is already spreading somewhat faster as a result, McClure said.

Search began in 1992

The search for a natural enemy of the adelgid began in 1992; without it, McClure said at the time, the hemlock forests might well be doomed, like the American elm (a victim of Dutch elm disease, an import) and the chestnut (a victim of yet another imported blight).

That would be a big loss on two counts:

First, the hemlocks are extraordinarily beautiful: tall, growing to heights of 60 or 70 feet and living up to 600 years, with a pyramidal crown, branches that droop nearly to the ground and small, delicate needles that make the branches look almost feathery.

Second, the hemlocks are the keystone of a unique ecosystem. The hemlock canopy creates a dark, damp ecosystem that is home to a distinctive mixture of plants and animals, chiefly lichens, mosses and ferns, certain warblers and vireos, winter wrens, hermit thrushes, barred owls, salamanders, frogs, toads, shrews and voles.

Typically, hemlock stands grow along streams, and the shade they provide keeps the water temperature right for trout and other aquatic life that require cold water. Remove them, and the temperature rises and the aquatic ecosystem is transformed.

Pub Date: 3/04/98

Baltimore Sun Articles
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.