A tiny pest is sucking the life out of old-growth hemlock forests from Maine to Georgia.

The hemlock woolly adelgid likes to settle on tender needles, form sticky white sacks resembling a dusting of snow and begin to feed. Five years later, the depleted tree is dead.

An Asian pest thought to have arrived on ornamental plants in the 1920s from Japan, the adelgids went largely unnoticed until their numbers exploded in the 1980s.

Carried on the wind, birds' feet, backpackers' gear and landscapers' tools, the nearly microscopic aphidlike insects spread north from Virginia and more recently south into the Carolinas and Tennessee.

In Great Smoky Mountains National Park, the country's most-visited park, a five-man crew is working exclusively on combating the adelgids.

Kristine Johnson, the Smokies forestry supervisor, watched recently as the crew fired a soapy pesticide spray onto infested hemlocks in scenic Cades Cove.

"The tools are very limited," she said. "And there is no way to predict how successful or how comprehensive the controls will be."

Besides the sprays, chemicals are injected into the soil or directly into the infected trees. But this is time-consuming and impractical for hemlocks deep in the backcountry.

The best hope may be the introduction of a predator beetle called Pseudoscymnus tsugae. Also a native of Japan, the "Pt beetle" is the size of a poppy seed and lives solely to eat hemlock adelgids.

"I think it is going to help save some of the trees," said Jim Hart, executive director of the Friends of Great Smoky Mountains National Park support group. But "I don't think enough beetles can be produced to save the entire forest."

The Friends are pouring nearly $300,000 into the adelgid effort in the Smokies, paying to outfit the spraying crew and acquire the beetles.

Yet an estimated 7 million beetles are needed to rid the pests from the 520,000-acre national park straddling the North Carolina-Tennessee border. At $3 apiece, that is nearly $21 million.

Smokies officials say the beetle program and other controls may reach only 10 percent of the hemlocks.

Foresters compare the adelgid threat to the blight that killed off American chestnuts in the 1930s and 1940s, attacking trees of all ages, from saplings to centuries-old treasures.

Although beneficial oaks supplanted the chestnuts, "there is not another evergreen that is going to replace hemlock in many settings," Johnson said.

Hemlocks provide much of the shade to cool mountain streams. "When you lose that overstory component of hemlock, you have a cascading effect on other species," Johnson said.

From the wood thrushes that nest in the trees to the insects and minnows that feed trout in once-canopied habitats, the ecological balance could be changed forever.

In Virginia's Shenandoah National Park, 80 percent of the hemlocks have died since the adelgid was first identified in 1988.

"We have an overlook called Hemlock Springs Overlook," park spokeswoman Karen Beck-Herzog said. "We recently took down the sign because there are only dead hemlocks now. It had become a kind of joke, 'Dead Hemlock Springs Overlook.' "

Shenandoah managers are working to save 100 to 200 acres of trees -- down from 3,000 acres -- with hopes of preserving a seed stock for replanting.

The adelgid reached the North Carolina side of the Smokies in 2002. It has now spread to the Tennessee side as well.

More than 70 infested sites have been confirmed among the Smokies' 8,500 acres of hemlock. Some trees are more than 400 years old.

The National Park Service, the U.S. Forest Service, state governments and local volunteer agencies are making "an aggressive, concerted effort" to fight back, Smokies spokeswoman Nancy Gray said.

The problem has been a lack of predator beetles, with only three private or state labs supplying them in Pennsylvania and New Jersey. Clemson University and the University of Tennessee are now producing beetles, too.

At the UT lab in Knoxville, about 50 miles from the park, beetles are raised in warm, humid comfort in specially designed clear plastic cases with plenty of fresh-from-the-Smokies adelgids -- the only food they eat.

"The beetles are not hard to rear. It takes about a month from egg laying to becoming an adult, but it is quite labor intensive," said entomologist Ernest Bernard, who runs the UT lab.

More than 52,000 beetles have been released in the Smokies, and the UT lab hopes to increase production to about 100,000 beetles next year.

The beetles are voracious. Tests in Connecticut and Virginia found the beetles can reduce an adelgid population in a test site by half in five months.

The tiny predators were unknown to science until Mark McClure of the Connecticut Agricultural Experiment Station found them during a trip to Japan in 1992 and brought them back to Connecticut, where adelgids first appeared in 1985.

After three years of study, more than 170,000 beetles were released in Connecticut from 1995 to 1999. Today, not enough adelgids are left to support another beetle release, said Carole Cheah, a colleague of the now-retired McClure.

"We have a slightly more positive attitude today because we are seeing trees recover," Cheah said. But she wonders whether an unusually cold winter did as much to kill the adelgids as the beetles.

"I still think the jury is out as to the effects of the biological controls," Cheah said.

Although it looks as if it is dusted with snow, this hemlock in the Smokies is infested with adelgids. "The tools are very limited," Great Smoky Mountains National Park forestry supervisor Kristine Johnson said of combating the hemlock woolly adelgid. University of Tennessee entomologist Ernest Bernard looks at an adelgid in his laboratory. Bernard grows predator beetles to counter the adelgids.