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CHEYENNE — The mountain bark beetle epidemic may be slowing in southern Wyoming, forest officials say, as the insects are running out of adult lodgepole pine trees to infest.

But the mountain bark beetle continues to ravage through western and northeastern Wyoming, though it is disputed whether the recent cold snap may have helped slow their pace.

The beetles have infested more than 700,000 acres of forest in southern Wyoming and 2.9 million acres in Colorado, according to a U.S. Forest Service aerial survey released Friday. That’s up from 2.5 million acres infested in 2008.

The beetles kill pine trees by boring into them to feed and reproduce, leaving behind large stands of dead trees in their wake. While pine beetles have always been a part of Rocky Mountain forests, warmer temperatures and drought have caused the beetles to flourish in recent years.

While the spread of bark beetles can’t be stopped, the worst of the epidemic may be over in Medicine Bow National Forest, as there are few stands of lodgepole pines — the beetles’ tree of choice — left to infest.

As of 2009, the beetles had either infested or killed 571,000 acres of forest in Medicine Bow — up about 116,000 acres from 2008, said Kathy Roche, a Forest Service ecologist at Medicine Bow.

By now, almost all the national forest’s stands of lodgepole pine have been affected, she said.

As a result, the hungry beetles are now turning to young lodgepoles, isolated lodgepoles mixed with other types of trees, and other types of pine trees that aren’t as popular with the insects, Roche said.

“They go, ‘Oh, I can’t find what I want, I’ll go to a nearby tree and try attacking it,’ ” she said. “And they can be successful in killing that tree, but they’re not successful in raising a brood of beetles that can go out and attack the next year.”

Roche hesitated to say that the end is in sight for the bark beetle epidemic in Medicine Bow, as it is unclear how many isolated lodgepoles are left in the national forest to pick off.

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But, she said, “I would not expect another million acres added next year for this whole area (of southern Wyoming and Colorado).”

However, the beetles show few signs of stopping in western Wyoming and the Black Hills region in the northeastern part of the state. In Shoshone National Forest alone, an estimated 823,000 acres have been affected, according to a U.S. Forest Service media release.

The recent run of subzero temperatures across Wyoming earlier this month may have slowed the spread of bark beetles by killing its larvae, said ecologist Duane Short, wild species program director for the Laramie-based Biodiversity Conservation Alliance.

But several Forest Service officials and other forestry experts disagreed, saying the weather needed to be colder for a longer period of time to affect beetle populations.

Mountain pine beetles spend the winter lying dormant in trees and produce a natural antifreeze.

Contact Jeremy Pelzer at jeremy.pelzer@trib.com or 307-632-1244.

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Total acres of forest killed or infested by mountain pine beetles in southern Wyoming:
County20082009
Albany131,000202,000
Carbon362,000444,000
Converse5,80010,000
Laramie3003,300
Natrona34,00038,000
Platte90150
Source: U.S. Forest Service