Put Mike Blumenthal among that icicle-thin group of Pennsylvanians hoping for more subfreezing weather, the colder the better, stretching into March.

	Linda Spillers, Associated Press The woolly adelgids are the white clumps seen on a hemlock branch at the Rapidan Camp, the former presidential retreat of Herbert Hoover, in Shenandoah National Park near Syria, Va. Click photo for larger image.

Blumenthal, state Department of Conservation and Natural Resources forest health supervisor, said the second shivering winter in a row will help slow the spread of the hemlock woolly adelgid, (pronounced a-DEL-jid) a tiny aphid-like insect that is sucking the life out of Pennsylvania's state tree.

"The adelgid is the No. 1 threat to forest health in the East, and a winter like this one that we've had so far should really knock it back,'' Blumenthal said. "If the low temperatures we've been experiencing so far continue, that can put a hurt to it."

The hemlock woolly adelgid hitchhiked into the United States from Asia in the 1950s, probably in a shipment of plants, and is now well-established throughout the Appalachian Mountains from North Carolina to Maine.

The soft-bodied insects, only 1 millimeter long, overwinter on the underside of the flat hemlock needles. They secrete a white, waxy covering that looks like a tiny tuft of cotton candy or wool in which they lay eggs, and for which they are named.

Hemlocks are also harmed by other bugs -- mites and loopers -- and by drought. But the adelgid, which feeds on the sap in young branches, causing needles to drop prematurely and branches to die, can be the fatal blow.

Blumenthal said the Eastern hemlock, which makes up 5 to 10 percent of Eastern forests, is not a commercially important tree, but it does fill an important ecological niche in the Appalachian Mountains and forested regions stretching west into Wisconsin and northeastern Minnesota.

"The value of the hemlock, which is often found in stands along streams, is measured more in terms of water quality, wildlife cover, aesthetics and recreation,'' he said.

In Virginia, hundreds of thousands of hemlocks are dying along the ridges and in the eastern foothills of the Appalachian Mountains. All of the hemlock stands in Shenandoah National Park are infested, and 90 percent of the trees are dead or dying.

New Jersey has lost half of the 26,000 acres of scattered hemlocks in its forests.

The adelgid first appeared in southeastern Pennsylvania in 1969, and has been spreading north and west, moving rapidly into new territory, especially during and after warm winters, ever since. It has been found in 43 counties, up from 32 counties just four years ago. Allegheny County is among the recent additions.

The adelgids had moved west of the Susquehanna River near Harrisburg in the mid-1990s, Blumenthal said, but were knocked back by a particularly cold winter.

"It took them years to recover from that one,'' he said. "But now about half the state is infested, east of a diagonal that runs through State College to Somerset County. Eventually it will invade the entire state, but the speed of the assault will depend on the weather.''

After the mild winter of 2001-02, woolly adelgids were discovered in 17 additional counties in Pennsylvania. Following the cold winter of 2002-03, infestations were found in only two new counties, said Brad Onken, an entomologist in the U.S. Department of Agriculture's Forest Health Protection Division in Morgantown, W.Va.

"The adelgids are moving from nymphs to maturing adults from now to the end of February, when they will start laying their eggs,'' he said. "At that time they are the most sensitive to colder temperatures."

A winged form of the insect develops early in the year and migrates to other hemlocks in the area. That, along with wind and birds, plus the biological quirk that all adelgids are female and therefore egg-layers, accounts for the insect's rapid spread.

Attempts to control the adelgids, which have few natural enemies in North America, have had limited success. Silvaculture control methods, such as timbering some trees to reduce the density of hemlock stands, don't work.

And although pesticides, horticultural soap and oil applications can be effective on ornamental plantings, they are too expensive and ecologically damaging to other plant and animal species for use in a widespread forest spraying program.

Several species of lady beetles in Asia feed on them and have been imported and released with some success. Blumenthal has overseen a program that has released more than 110,000 of the lady beetles in 18 counties since 1999. They appear to be overwintering well and reproducing, but control of the adelgids remains a distant goal.

The state and the U.S. Department of Agriculture are also experimenting with the introduction of a smaller black beetle that will actively feed on the adelgids during the fall and winter.

"The new beetle is native to the northwestern U.S. and has done a good job in Canada and China,'' Blumenthal said. "We hope it will move us toward solving this problem and bringing the adelgid into some balance.''