Trees, which the beetles feed on, can become infected and die, proving to be a safety hazard for people hiking in the mountains.
Forestry experts say the mountain pine beetle epidemic that ravaged Colorado's lodgepole pines for two decades is over, but a second bug that attacks spruce trees is still spreading.
A yearly report on the state's forests released Thursday says mountain pine beetle activity has "subsided and remains low" after attacking more than 5,300 square miles of trees since 1996.
"The epidemic has ended in many areas of Colorado as mature pine trees have been depleted in the core outbreak areas," according to the Colorado State Forest Service and U.S. Forest Service.
However, in 2015, spruce beetle infestations were detected on 409,000 acres across the state, expanding onto 182,000 acres of previously unaffected forests.
Since 1996, spruce beetle outbreaks have caused varying degrees of tree mortality on more than 1.5 million acres in Colorado.
The report had good news about aspen trees, which splash mountainsides with bright colors every autumn: They're generally faring well after suffering worrisome die-offs from drought in previous years.
Read more in the 2015 aerial detection survey.
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