Mountain pine beetles inhabit Montana pine trees such as the Ponderosa Pine and Lodgepole Pine. During early stages of an outbreak, attacks are limited largely to trees under stress from injury, poor site conditions, draught, fire damage, overcrowding, root disease or old age. As beetle populations increase, the beetles attack most large trees in the outbreak area.
The beetles kill the trees by boring through the bark into the phloem layer on which they feed and in which eggs are laid. Pioneer female beetles initiate attacks, and produce pheromones which attract other beetles and results in mass attack. The trees respond to attack by increasing their resin output in order to discourage or kill the beetles, but the beetles carry blue stain fungi which, if established, will block the tree resin response. Over time (usually within 2 weeks of attack), the trees are overwhelmed as the phloem layer is damaged enough to cut off the flow of water and nutrients. In the end, the trees starve to death, and the damage can be easily seen even from the air in the form of reddened needles. Entire groves of trees after an outbreak will appear reddish for this reason.
The beetle is responsible for massive damage to Lodgepole pine forests in Montana, Colorado, Wyoming, Idaho, Washington, Oregon, California, and Canada where a reduction in the severity of winters has allowed the population to explode.
Higher average temperatures would assist the beetle to increase in population and range. However it was unusually cold in northern Colorado through the 2009/10 winter, and some people with mountain properties thought their pine beetle problems were over. Unfortunately, cold winter weather can kill off the insects, but it has to be extreme: 30 below zero for five days or more.
In winter months, pine beetles are in the larval stage, snugly settled in beneath the bark. The larvae actually produce antifreeze in their bodies, and as it gets colder, they produce more of the chemical. That’s why they’re well protected from the cold. However, sudden cold snaps in fall or late spring can do them in, because the antifreeze protection is weaker at those times.