Amy Gannon, hatchet in hand, sliced a slab of bark from a lodgepole pine tree near Wolf Creek, Mont., and quickly spotted a mountain pine beetle larva no bigger than her pinky fingernail.

"This tree's done for," said Gannon, an entomologist with the Montana Department of Natural Resources and Conservation.

As wildfires roar through tinder-dry forests in California, the mountain pine beetle is silently killing even more trees — hundreds of thousands of acres of towering trees, mostly lodgepole pine, according to Robert Mangold, director of Forest Health Protection for the U.S. Forest Service.

An epidemic of this magnitude hasn't been seen in the Mountain West in 25 years, he said.

In 2007, the beetles were blamed for killing 3.9 million acres of trees in Colorado, Montana, Wyoming, Oregon, Idaho, Utah and Washington, Mangold said.

By comparison, the fires in California had burned 640,847 acres as of July 14 this year, according to the National Interagency Fire Center. An average of 3.4 million acres has burned nationally each year since 2003, according to the center.

The current pine beetle infestation is the worst since 1981, when 4.7 million acres of trees were infected, Mangold said. He blames the outbreak on a perfect storm of drought, large stands of old trees and, possibly, warmer temperatures because of climate change.

"It's shocking," said Jeff Witcosky, an entomologist for the U.S. Forest Service in Lakewood, Colo. "We talk about the grieving process."

While the impact has been enormous, Mangold said, the mountain pine beetle is a native insect that, along with fire, does play a role in the regeneration of lodgepole pines.

The pines have a hard cone that won't open without a hot fire, he said. When the cones open, they dump out seed, creating a thick forest of trees of the same age. When the trees hit 80 to 90 years old, they weaken and become susceptible to the mountain pine beetle. The beetles kill the trees, creating more dry fuel for those fires, he said.

This month, the adult beetles are emerging from trees and looking for hosts they can bore into to mate and lay eggs, Gannon said. The beetles feed on the inner bark, severing the tree's circulation, she said.

The large number of affected acres is increasing the risk of large fires as the Northern Rockies enters the fire season, said George Weldon, deputy director of fire, aviation and air for the U.S. Forest Service's Northern Region.

"When there's red needles on the trees, those trees are a lot more flammable," he said.

After the needles fall off, the fire risk is reduced, but if the dead trees are not harvested, they create even more fuel for fires, he said.

Signs of bigger problems

The Northern Region of the Forest Service is spending $15 million a year to reduce hazardous fuels around communities, including trees felled by the beetle, Weldon said. The region is made up of Montana, northern Idaho and North Dakota.

Jesse Logan, a forest ecologist in Emigrant, Mont., sees evidence of a bigger problem in the beetle infestation than fire: global warming.

"This is one of the canary-in-the-coal-mine warning signs," he said.

The beetles are now moving into higher elevations, where bitter winter temperatures used to keep them at bay, Logan said.

Once there, the bugs are attacking species besides lodgepole with new vigor, such as whitebark pines around Yellowstone National Park and the jack pine in British Columbia, Canada, he said.

"It's like a new invasive species," Logan said

The whitebark pine produces seeds that are a critical staple in the diet of grizzly bears, Logan said. Fewer pines of all kinds also means less shade cover for cool-water mountain streams where trout thrive, he said.

The trees also hold snow in place, slowing mountain run-off so water is available for irrigation deeper into the summer.

Mangold agrees warming temperatures are playing a role in the current outbreak.

"But the forests are in a state where we'd have this kind of epidemic probably with or without these temperatures," he said.

Gordy Sanders, resource manager for Pyramid Mountain Lumber in Seeley Lake, Mont., which produces boards from logs, said the infestation is "devastating the countryside." Anyone who owns standing timber is losing aesthetic land value, he said.

Slowing the spread

To ward off the pests, chemicals that mimic those produced by the beetles, causing them to pass the trees because they sense they are full of other beetles, are sometimes applied to high-value trees around campgrounds and homes, but the treatments are expensive, said Ken Gibson, an entomologist with the U.S. Forest Service in Missoula, Mont.

Forestry practices, such as thinning thick stands of pure species of trees, can also slow the spread, he said.

"We don't have to sit around and watch trees die," he said.