CHEYENNE, Wyo. — After killing millions of acres of trees across Wyoming over the past 16 years, the mountain pine and spruce beetle epidemic is nearing the end of its course, mainly because the pests don't have much more left to eat.
"They've run out of food," state Forester Bill Crapser said Friday. "So they're on the decrease."
An aerial survey indicates that both mountain pine beetle and spruce beetle activity slowed last year across Wyoming's forests, except for the Black Hills National Forest area in the northeast part of the state, according to the U.S. Forest Service.
Statewide, the number of new acres with mountain pine beetle declined from 719,000 in 2011 to 180,000 acres in 2012. The mountain pine beetle outbreak in Wyoming has affected 3.4 million acres of forest since 1996. In 2011, the total acreage for the epidemic was 3.3 million acres.
Spruce beetle activity statewide has declined from 76,000 acres in 2011 to 32,000 acres in 2012. Since 1996, 558,000 acres have been affected by spruce beetle in Wyoming.
Declines in beetle activity have been seen in the Medicine Bow, Shoshone, Wasatch-Cache and Bridger-Teton national forests as well as the Sierra Madre, Snowy Range and Medicine Bow mountain areas.
"They've gone through so much of the acreage that we're seeing a real decrease in the amount of expansion," Crapser said.
Areas attacked by the beetles stand out because of the thousands of dead, brown trees they leave standing among the remaining healthy, green trees that escaped the bugs.
Crapser said the Bighorn National Forest is the only area in north-central Wyoming that was relatively unharmed. However, there are small pockets of beetles in the Bighorns that could expand, he said.
While the mountain pine and spruce beetles are declining, foresters have noted a slight increase in the ips beetle in Wyoming, Crapser said.
In addition, foresters are watching an outbreak of emerald ash borer in the Great Plains to see if it spreads into Wyoming, where ash trees are mainly located in cities and towns, he said.