Earth Notes: Bark Beetles in a Warming West

Jun 6, 2012

For many residents of the mountain west, warmer temperatures may not sound too bad.

But small differences in temperature can make a big difference.

Consider bark beetles. They’re native to the region’s conifer forests. Normally, the insects emerge in summer. Females bore into the cambium layer of trees and sever vessels that contain resin, releasing a sticky flow that “pitches out” the beetles. But in weaker trees that lack sufficient resin swarms of beetles can quickly chew enough wood tunnels to kill their hosts.

Over the last decade, drought and unnaturally dense forest stands have stressed trees so that multitudes can’t defend themselves against the bugs. A huge die-off of piñon and ponderosa pines has resulted.

But it’s not just drought that foresters worry about. With the coldest winter temperatures higher than they once were, more bark beetles can survive the winter. That means a double whammy for the region’s pines, says Northern Arizona University forest entomologist Rich Hofstetter.

Researchers in Boulder, Colorado, recently witnessed adult mountain pine beetles taking flight and laying eggs in June and July instead of the usual August. For that region, it meant two, instead of one, generations of that beetle species that year—with significantly more bugs available to attack trees.

A similar increase in insects could spell trouble for pines and other conifers on the Colorado Plateau. That’s why Hofstetter and his students are closely monitoring the region’s beetles—so that they can learn what the future might hold for pines on the plateau.