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Creepy critters resilient in Western Pennsylvania cold

| Monday, Feb. 3, 2014, 11:34 p.m.

This winter has been a bad one, but experts say it's unlikely that temperatures in Pennsylvania have been cold enough to slow the spread of invasive pests such as the emerald ash borer.

“Some of these insects are incredibly cold-hardy,” said Matthew Ginzel, a professor of entomology at Purdue University. “Whether ash borers die in significant numbers depends on the level of cold. There probably has been some winter kill, but it's confined to certain areas.”

The Asian beetle was identified in the United States in 2002 in Southeastern Michigan and found in Pennsylvania in 2007 in Cranberry. Tens of millions of ash trees have been lost to the pest, which usually kills ash trees within three or four years of an infestation.

The state estimates about 300 million are in ash trees in Pennsylvania, and the beetle has been reported in 47 of the state's 67 counties.

According to a study by the U.S. Forest Service, a temperature of 20 degrees below zero could kill about half of the larvae of the emerald ash borer. Temperatures of 30 degrees below zero would kill about 98 percent.

“That's significant in some parts of the country but probably not in Pennsylvania,” said Robert Venette, a research biologist with the Forest Service in Minnesota and the study's author.

The coldest official low temperatures recorded in Pennsylvania were minus 15 in Bradford, Indiana and Washington, according to Accuweather. The winter's low temperature in Pittsburgh was minus 9 on Jan. 7.

“The winter has not been as cold as many people think,” said Tom Kines, an Accuweather meteorologist. “We have had some cold days. But there have been some mild days thrown in.”

Green emerald ash beetles die in the fall, and larvae burrow inside trees during the winter. The larvae do something entomologists call “supercooling” when temperatures first begin to drop in the fall.

“They then produce an antifreeze-like substance so that the water in their cells does not crystallize,” Ginzel said.

Native to Northeast Asia and Eastern Russia, the beetles were accustom to cold weather before they arrived in the United States.

Cold snaps and heavy thunderstorms can reduce populations of the hemlock woolly adelgid, another non-native, invasive insect, according to the Pennsylvania Department of Conservation and Natural Resources. It feeds on hemlock trees in eastern North America, including Pennsylvania.

Rick Wills is a staff writer for Trib Total Media. He can be reached at 412-320-7944 or at rwills@tribweb.com.

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