USDA image of the woolly adelgidThe Friends of Hemlock Gorge

The Threat of the Woolly Adelgid

The hemlock woolly adelgid (Adelges tsugae Annand), is a small aphid like insect that feeds on several species of hemlock (Tsuga species). It was introduced into North America in Asia, its homeland. It has been recognized in the United States since at least 1924. By sucking sap from the young twigs, the insect retards or prevents tree growth causing needles to discolor from deep green to grayish green, and to drop prematurely. The loss of new shoots and needles seriously impairs tree health. Defoliation and tree death can occur within several years. It is a serious threat to the hemlocks not only of Hemlock Gorge, but all of New England.

It has advanced into Southern Massachusetts, and it has appeared in the Gorge and in nearby forest. The threat it poses is serious, and the Friends of Hemlock Gorge are working with the MDC to develop a strategy that could be implemented now that the woolly adelgid has appeared in Newton. The approval of $60,000 by the legislature (July 31, 2000) to grow and release ladybugs (see below for sites that describe their use) holds out the promise that meaningful control may be achieved in time to save some of the hemlocks in the reservation.

Knowledge is power, and here are some sources of information about the woolly adelgid.

Finally, we quote here a news story on the adelgid published by the State House News Service in September, 2000 and reprinted here with the permission of the author..


September 12, 2000

By Elisabeth J. Beardsley
[email protected]


The Bay State's official bug could soon wing to the rescue of one of the state's favorite native trees.

Under a $60,000 pilot program included in this year's budget, an army of Japanese ladybugs 10,000 strong will be brought to bear on the woolly adelgid, a nasty little insect that's killing hemlock trees in this state and others along the East Coast.

The sap-sucking Asian aphids were introduced into North America in the 1920s, and have slowly been spreading northward. The woollies have ravaged Connecticut forests for years, and turned up in Massachusetts after being blown across Long Island Sound on the winds of a hurricane five years ago.

The pilot project will begin in Hemlock Gorge in Newton Upper Falls, an area particularly beset. Sen. Cynthia Creem (D-Newton) helped secure the money for the ladybugs, which are natural predators of the aphids, after taking Senate President Thomas Birmingham to the gorge to see the damage.

"You can see that the trees are dying, that the leaves don't look good. You can see where they've changed color," Creem said, adding that the 23-acre reservation is "gorgeous" and "means a lot to a group of people."

In addition to the threat to the forest, Creem said local officials are being whacked with the cost of removing dead trees. Brookline spent $10,000 last year removing dead hemlocks from the gorge, she said.

Newton Alderman-at-Large Brian Yates, president and founder of Friends of Hemlock Gorge, said pesticides can be sprayed or injected into trees' root balls, but it's a temporary solution that can't be used near water or on very large trees. Chemicals can be effective for a small number of trees, such as in a yard, but the risk of re-infection makes pesticides impractical for forests, Yates said.

The Friends of Hemlock Gorge hit upon the ladybug idea after a Connecticut researcher traveled to the adelgid's native Japan in 1992 to find out why the hemlocks there were healthy, Yates said. He discovered that a poppy-seed-sized black ladybug, previously unknown, was keeping the adelgid population under control by eating the aphids' egg sacs, which look like strings of fluffy little white balls.

The Japanese hemlocks "never got to such a stage that they would be vulnerable to dying because there were natural predators there," Yates said. "In Japan, they're in perpetual balance. We're trying to establish the balance."

After two years of research, the US Department of Agriculture issued a permit for the introduction of the ladybugs. Since 1995, 18,000 of them have been released into six hemlock forests in Connecticut and one in Virginia, reducing the adelgid populations by between 47 and 100 percent.

Sen. Stephen Brewer (D-Barre), whose district is also suffering an aphid infestation, has called a hearing on the menace this Thursday before his Special Commission on Forest Management Practices. With the virtual extinction of the American elm in mind, Brewer said, environmental managers must act now to stop the bugs' northward march. They have already reached the Vermont and New Hampshire borders.

"They don't pay any attention to political boundaries. Nature has its own agenda," Brewer said. "They go into other areas and will upset the economy and strike an aesthetic blow to our environment."

Hemlock fans are anxious to get the ladybug breeding project underway, hoping to release them into Hemlock Gorge next spring, Yates said. But the Metropolitan District Commission, which oversees project funding, has not yet chosen a breeder, he said.

MDC spokesman Chuck Borstel said Commissioner David Balfour and agency officials are discussing project priorities. The ladybug pilot is in limbo until the agency decides whether lawmakers appropriated enough money for it, he said. "Sometimes legislative estimates are not always accurate," Borstel said. If the project gets a green light, he said the MDC would likely hand the money over to the Department of Environmental Management to figure out the details.

Not everyone is thrilled about the prospect of turning Massachusetts into ladybug-land. The Massachusetts Audubon Society is wary of the untrammeled use of "biological control agents" insects released to kill other, peskier insects. It's suspected that such attack bugs had a hand in the extirpation of the Regal Fritillary butterfly from Nantucket and Martha's Vineyard.

Christopher Leahy, director of Mass. Audubon's Center for Biological Conservation, said environmentalists are worried about the fact that Eastern Hemlocks are "next on the storm track" for the woolly adelgids, but they're also concerned that the ladybugs might attack "good aphids," as well.

"The worry is always that the foreign control agent may be worse than the species it was placed there to control in the first place," Leahy said. "It's a fairly new science, this biological control thing. The intricacies of biological interactions are such that we can't possibly get our arms around them and know them well enough to predict accurately what's going to happen."

But Yates said the habits of the Japanese ladybugs are well known, and they only prey on woolly adelgids and one other type of insect, the latter of which makes the ladybugs infertile. "This is a very species-specific predator," Yates said.

Brewer said he's anxious to hear the pros and cons of biological agents, but he noted that natural predators are probably better than spraying noxious pesticides, which can seep into the water table and cause further harm to plants, animals and humans.

And Creem added, "What's the other answer? Let all the hemlocks die?"

As these resources make clear, there is a solution may be at hand for the woolly adelgid, but the battle is far from won. If you share our concern with the Woolly Adelgid, please consider participating in, and contributing to, the activities of the Friends of Hemlock Gorge.

Page last updated March 17, 2002

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