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Beetle Infestations in Our Forests

While many people associate drought and forest fires with global warming, climate change is spreading another epidemic in North American forests. The mountain pine beetle, which is no bigger than a grain of rice in size, has destroyed millions of pine trees in the United States and Canada. The beetle is considered by some to be the most damaging insect blight ever seen in North America and there is little anyone can do to stop it.

Until the 1990s, the mountain pine beetle was listed as a beneficial insect. It only attacked weak, dying trees which allowed younger pines to gain a foothold on the forest floor. Under normal conditions, cold winters kept the population in check. But as winters have grown milder—and summers hotter and drier—the pine beetle has been cutting a swath of destruction through strong, healthy forests.

A mountain pine beetle attack can kill a tree within a year. The adults bore into the trees in mid-summer and lay eggs just under the bark. The beetles introduce the bluestain fungus to the pine. When the larvae hatch they feed on the tree tissue between the bark and the wood. The fungus growth assists the beetle in killing the tree. In addition, the fungus prevents water and nutrients from flowing through the tree. The larvae grow into adults and find new trees to lay eggs. Each female can produce about 80 eggs which allows the population of mountain pine beetles to grow rapidly. Insects emerging from a single tree can infect several other trees.

Pines that are infected by the beetle show popcorn-shaped masses of resin, called pitch tubes, where the tunneling begins. The foliage of the crown turns red or yellow as the tree is deprived of life-giving water and nutrients.

There is no effective means for controlling the beetle outbreak. Between 2009 and 2010 there was a 10-fold increase in pine beetle activity in Colorado’s Front Range. Millions of acres of trees in North America have died as a result. In British Columbia, more than 44.5 million acres of pine forests have been affected. The beetle has also caused extensive damage in Wyoming and South Dakota. Only sustained temperatures of around -15°F can slow the spread of the beetle. In addition to effecting timber harvests, watersheds, wildlife habitat, and scenic sites, the beetle-killed trees are causing a buildup of highly flammable fuel responsible for catastrophic wildfires throughout the mountain west.