SPRINGFIELD, Mass. – The region’s bitterly cold winters may be hard on New Englanders, but they have been even harder on an Asian insect that’s threatening to destroy hemlock forests from Maine to Georgia.

The wooly adelgid – an insect no bigger than the period at the end of this sentence – sucked the life out of 95 percent of the hemlocks in Virginia’s Shenandoah Valley and has pushed north into New England’s hemlock forests.

It arrived in Massachusetts about 15 years ago, but so far the damage has been spottier, with scattered pockets of dead trees marked by the signature clusters of white tufts on the undersides of branches.

Researchers believe successive winters of below-normal temperatures have slowed the adelgid’s northward progress. This summer, researchers found that 86 percent to 99 percent of the adelgids in central and western Massachusetts have been iced.

“We haven’t had a population this low since it was first discovered in 1989,” Bob Childs, director of the Urban Forestry Diagnostic Laboratory at the University of Massachusetts said.

Scientists have long suspected adelgids (pronounced ah-DEL-jids) were susceptible to below-freezing temperatures, which may explain why the damage has been less severe in the insect’s northern range.

“We’re not seeing the widespread devastation in the southern forests. We are not even seeing the damage that Pennsylvania and southern Connecticut have received,” Charles Burham, head of forest health for Massachusetts said.

A wet spring also helped the water-loving hemlocks that were damaged to recover, he said.

“It’s definitely been slowed, but there are still concerns,” Dennis Souto of U.S. Forest Service’s Durham, N.H., office said.

In Connecticut, where researchers discovered an Asian ladybug that has proved to be one of the best defenses against the adelgid, the winter kill has been so severe that officials are importing adelgids from Pennsylvania to keep their research stock of poppy-seed sized ladybugs going.

“It’s a message of hope,” said Carole Cheah, who has been working with the beetles at the Connecticut Agricultural Experiment Station since 1992.

Similarly, New York foresters have found the adelgid confined primarily to the warmer southeastern section of the state, except for an isolated outbreak near Rochester, Souto said.

Still, Maine, Vermont and New Hampshire have established strict quarantines to protect one of the signature trees of the northern forest. And they have been vigilant in searching down and burning hundreds of infected trees, Souto said.

By any measure, the adelgid, which was accidentally introduced from Asia in the 1920s, is a strange creature.

Unlike most native forest insects, it’s dormant in the hot summer months of July and August and active during the fall and winter.

All wooly adelgids are female, reproducing asexually to lay broods of eggs in cottony masses on the underside of hemlock branches.

The tiny larvae attach themselves to the base of the needles and prevent new growth while at the same time sucking the life out of the tree. Most adults are wingless and remain on the hemlocks, but a few sprout wings. However, they can only reproduce on certain Japanese spruce, and in American forests they die when they set off looking in vain for the spruce.

Despite their tiny size adelgids can kill a hemlock in five to 10 years with trees on rocky ridges, and those subject to dry conditions, most vulnerable, Souto said.

With its feathery dark branches, the hemlock is one of the most common trees in the eastern forest and is also popular for landscaping.

“I can’t think of another insect except the gypsy moth that has generated such interest,” said Cathy Sparks, a forest health specialist for Rhode Island, who is surveying nurseries and residents to determine the economic impact of the adelgid on the state.

Homeowners can use oil sprays to combat the wooly adelgid on ornamental hemlocks, but options are few in the forest.

And, while encouraging, the jury is still very much out on whether the adelgid will remain susceptible to below-freezing temperatures.

“If we are removing 95 percent of the population every winter, then the 5 percent that survive could develop a more cold hardy population,” Souto said. “Insects are very adaptable and there are a lot of questions in dealing with exotic species that we don’t have an answer to.”

On the Net: U.S. Forest Service: www.fs.fed.us/na/morgantown/fhp/hwa/hwasite.html