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W.Pa. trees get reprieve from gypsy moth attacks; other regions not so lucky

| Sunday, March 24, 2013, 12:01 a.m.
Cynthia Walter, an associate professor of biology at Saint Vincent College in Latrobe, and her students have been researching the health of woodlands near the Laurel Summit and Powdermill Nature Reserve. Portrait taken on the Saint Vincent College campus in Unity Township on February 28, 2013. Guy Wathen | Tribune-Review
A female Gypsy Moth and egg mass on the Saint Vincent College campus in Unity Township on February 28, 2013. Guy Wathen | Tribune-Review

The gypsy moth caterpillars that have feasted on Western Pennsylvania's trees for 24 years won't defoliate the region's forests this year, sparing the oaks and other hardwoods that have recovered from the heavy toll exacted by serious infestations, experts said.

“The trees are healthy, and no defoliation of hardwood trees was noted last year,” said Edward Callahan, district forester for Forbes State Forest, which has 60,500 acres in Fayette, Somerset and Westmoreland counties.

But that doesn't mean the end of the destructive insect with the voracious appetite that caused the timbering of some infested trees from Ligonier Township to Mt. Davis in Somerset County.

Despite intensive spraying programs that cost more than $17 million from 2006 to 2009, state foresters said they can't eliminate the pest.

“The gypsy moth will continue its cyclic population with ups and downs, and we cannot eradicate the insect. It's too well established, and is here to stay,” said Secretary Richard J. Allan of the Department of Conservation and Natural Resources.

“Five years down the road, we might see (gypsy moths) again” in Forbes State Forest, Callahan said from his office in Laughlintown.

Ferocious attacks

The 2-inch gypsy moth — it lives about a year and eats leaves during its caterpillar stage — feeds on more than 200 species of trees and shrubs. It defoliates oak, apple, birch, poplar, willow and other trees common to Western Pennsylvania.

Foresters believe the pests will strike this summer in northcentral and northwestern Pennsylvania, said David A. Schmit, a forest health specialist for the state Bureau of Forestry.

To combat the impact of the growing gypsy moth population in that region, state, federal and local governments plan to spend as much as $2 million this spring to helicopter-spray Bt, or bacillus thuringiensis, a biological insecticide, over about 43,100 acres of state forestland, parkland and game commission land in Cameron, Clarion, Forest, Jefferson, Lycoming, Potter and Tioga counties.

The insecticide, which kills the caterpillars when consumed, also will target 65 acres of private forest in Venango County.

Spraying has not been necessary since 2009 because the gypsy moth's natural enemy, a fungus, caused populations to decline across the state, said Daniel Devlin, forestry bureau director.

In 2009, the state sprayed more than 178,380 acres in 25 counties. That was done on the heels of a 2008 program that spread Bt over 221,221 acres of private, state and federal woodlands in 27 counties.

The severity of an outbreak in the spring can be predicted by an egg mass count the previous fall, barring the use of a fungus, spraying or other predators to control gypsy moths, Callahan said.

Each small, tan egg mass that clings to a tree might contain 400 to 800 black pellet-like eggs, according to Penn State's College of Agricultural Sciences.

The forestry bureau tracks the defoliation of woods through aerial mapping, then conducts a ground inspection to determine what is causing the damage, Callahan said.

“We don't predict what is going to happen; we map the actual defoliation,” he said.

A healing process

About 700,000 acres of woodlands in Pennsylvania were defoliated by the gypsy moth in 2006, according to the state conservation department.

At least half of all oak trees in the state were lost in the initial infestation. Fewer died in the next year, because there were not as many leaves to eat and natural predators attacked the gypsy moth, according to Kurt W. Gottschalk, research forester for the U.S. Forest Service in Morgantown, W.Va.

Gottschalk, a project leader for the service's Ecology and Management of Invasive Species and Forest Ecosystems unit, said some areas east of Forbes State Forest have endured four gypsy moth outbreaks during nearly three decades.

The insects hit the ridges of Laurel Hill in Westmoreland and Somerset counties with ferocity from 2006 to 2008, defoliating forests south of Route 30, then moving to Mt. Davis, the highest point in the state, in southern Somerset County, Callahan said.

After Forbes State Forest lost about 1,500 acres of trees in the last defoliation, some damaged trees were cut for timber, Callahan said.

Cynthia Walter, an associate professor of biology at St. Vincent College near Latrobe, has headed a gypsy moth research project and worked on long-term ecological studies in forests and streams for more than 25 years.

Trees don't die because of the loss of leaves. Rather, “they often succumb to a fungal infection,” Walter said. The stress of growing new leaves and trying to ward off pathogenic fungi can be damagaing for weakened trees, she said.

A tree begins to suffer when 30 percent or more of its leaf surface is lost, leaving it susceptible to disease, drought and attack by other insects. Walter compares stress on trees — caused by droughts, high temperatures and pests such as the gypsy moth — with a boxer taking a punch.

“The fighter has not gone down yet. Some of the oaks are still standing. They are nice and strong. A lot of red maples are coming back to our forest,” Walter said.

The affected areas in Forbes State Forest have recovered because of the variety of trees in Pennsylvania, along with fungus, pesticide spraying and wasps that were introduced to kill the moth, Walter said.

At Powdermill Nature Reserve near Rector, Ligonier Township, there was “a little bit of mortality, but our diversity helped Powdermill recover,” Walter said. She has worked with her students over the years to monitor the forest at the nature reserve.

“The Powdermill forests are quite vigorous,” Walter said.

That diversity of trees also helped Forbes rebuild. “They never experienced a huge die-off,” she said.

Joe Napsha is a staff writer for Trib Total Media. He can be reached at 724-836-5252 or jnapsha@tribweb.com.

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