FORT COLLINS – Mountain pine beetles are getting ready to emerge and fly, which means Colorado residents should check their remaining firewood stock now to ensure they are not aiding the infestation of urban or neighboring trees.

“Wood that was properly dried, or seasoned, before last fall presents little risk of harboring the mountain pine beetle, as any beetles taking up residence in dried wood have already flown,” said Ingrid Aguayo, forest entomologist for the Colorado State Forest Service, a division of the Warner College of Natural Resources at Colorado State University. “However, wood that was green last fall, winter and spring should be checked for signs of infestation, and residents should take extra caution when replenishing wood stocks with green wood in the upcoming months, as most of the beetles will fly from July through September.”

The presence of small, BB-sized holes in the bark indicates that the wood was infested, but the beetles completed their development and have already flown from that piece of log, Aguayo said. However, bark from wood cut last winter and spring can easily be removed from the wood, and the infested wood can be readily identified.

The soft inner bark, or cambium layer, of trees is where the beetles breed and their larvae live. The one-third to one-fourth-inch larvae are white with small brown heads. Due to the long drying time pine require, larvae can live in the cambium from the fall through spring months after a tree is cut. At this time of year, much of the larvae may already have entered a pupal state or may be approaching adult status.

“The best treatment for infested wood is to debark or burn it,” Aguayo said. She noted that some firewood may also be infested with Ips beetles, which are difficult to distinguish from mountain pine beetles while in the larval stage. Ips beetles tend to breed in freshly cut green pine, but are much less likely to attack healthy pine trees. At any rate, they do provide a small risk and the wood also should be burned or debarked before July.

Solar treatment is an environmentally safe method of treating wood without burning; however, with less than a month to go before some beetles fly, it is too late for solar treatment this year. Solar treatment also is not recommended for high elevations, so mountain residents should consult their local Colorado State Forest Service district office for more information prior to treatment at

When buying wood in the summer, consumers should confirm that they are only buying and using firewood that is already seasoned, especially if they do not know the condition of the trees from which the wood was harvested.

“If the needles were already red when the tree was cut, then the beetles have vacated the tree, and that tree is no longer a threat in terms of mountain pine beetle,” Aguayo said. “If the needles are still green and pitch tubes (popcorn-sized patches of resin from where the beetles bored through the bark) are visible, or larvae, pupae, and/or young beetles (light brown) are present under the bark, then it’s very likely the beetles will develop before the end of the summer. This wood definitely should not be transported out of the area of origin from July through September.”

More information about the mountain pine beetle is available at