Pine Beetles

by Nick Gromicko, CMI® and Kenton Shepard

The pine beetle, also known as the mountain pine beetle, is an insect native to the forests of western North America. Periodic outbreaks routinely kill Mountain pine beetle large stretches of pine forest and are a concern for homeowners in certain mountainous regions.

A few facts about the current pine beetle outbreak: 

  • The pine beetle primarily attacks lodgepole pines, ponderosa pines, Scots pines and limber pines. Of these species, the lodgepole pine is the most affected. Within the next three to five years, almost every lodgepole pine in the state of Colorado will have succumbed to infestation.
  • The pine beetle is a significant problem in parts of Colorado, Wyoming and British Columbia. The beetle affects all other western states to varying degrees.
  • As a result of warmer temperatures in recent years, beetle populations have grown unchecked and are the largest ever in known history in North America. For freezing temperatures to kill larvae during the middle of winter, temperatures of at least 30° below zero (Fahrenheit) must be sustained for at least five days.
  • In Colorado alone, pine beetles have killed more than 2 million acres of trees statewide since the outbreak began in 1996, with most of it in the past two years. In British Columbia, more than 9 million acres of forest have been substantially damaged or destroyed since 2002. Provincial and federal government scientists are predicting that more than 80% of all pine forests in British Columbia and Alberta will be killed by 2013.
  • Pine beetles can travel many miles per day, depending on air currents. They appear poised to sweep east to the Atlantic through Canada’s Jackpine Boreal Forest.

How are trees damaged?

Female pine beetles bore into a tree's vital inner bark, and then tunnel vertically, creating galleries. Upon entry into the bark, the female introduces aPitch tubes are signs of mountain pine beetle infestation fungus that impairs the tree's circulatory system and reduces its ability to repel the attack. The primary purpose of this fungus is to provide hatched larvae with a food source. Females emit a pheromone to attract males for mating, which also attracts other females, causing a mass attack. After mating, females lay eggs that hatch into larvae in several weeks. The larvae feed on the host tree as temperatures warm up the following spring. They tunnel horizontal galleries from the vertical egg chambers and eventually girdle the tree, killing it. By summer, the larvae emerge as adults and find new trees to infest.

Infected trees can be identified in the following ways:

  • Smaller-diameter trees are less likely to be attacked than larger-diameter trees. Pine beetles rarely attack trees smaller than 5 inches.
  • Popcorn-shaped masses of resin, called pitch tubes, may grow on the trunk where tunneling begins.
  • Boring dust may be visible in bark crevices and on the ground immediately adjacent to a tree base.
  • Galleries or tunnels can be found under the bark of the tree. Of course, removal of the bark to inspect for galleries may further damage the tree.
  • The tree may have discolored foliage. Pine needles usually turn red as the tree dies.
  • There may be evidence of woodpeckers feeding on the trunk. Woodpeckers and other small birds feed on pine beetles.
  • The sapwood may appear blue-stained. As a result of fungi introduced by the beetle, some of the wood may turn blue.

Defensible space and other concerns for homeowners:Map of areas affected by mountain pine beetle

Unfortunately, the most serious damage inflicted by pine beetles has nothing to do with aesthetics or lost tourism revenue. Wildfires, while natural and necessary, become far more devastating and widespread during pine beetle epidemics. Felled trees litter the forest, dry out, and make fires more likely. For this reason, individual property owners as well as whole communities have begun enlarging existing areas of defensible space to protect their homes. This summer, fire crews in the Colorado mountain towns of Vail and Aspen have cleared many acres of trees that had been killed by pine beetles in order to protect the communities from wildfire. Homeowners who live in areas affected by pine beetles need to examine their trees periodically for evidence of infestation in order to take steps to protect their homes from the potential spread of fire. Fire is not the only hazard posed by dying trees, however; they can shed their branches and needles on rooftops, clogging gutters. Falling trees can cause injury, death or property damage, especially on heavily forested properties. 

Tips that InterNACHI inspectors can pass on to their clients:

  • Do not store felled timber infested with pine beetles near healthy trees. It is possible for pine beetles to spread from infected firewood to adjacent trees. Experts advise that in order for felled trees infected by the pine beetle to be stored safely, they should be stripped of bark or burned before the beetles emerge in late spring. People have lost valuable trees by stacking infestedSwath of pines killed by the mountain pine beetle firewood on their property. Homeowners can also cover leftover firewood with two layers of clear 6mm plastic during the growing season (April to October). Plastic thinner than 6mm may be bored through.
  • Trees that are heavily infested must be removed and burned immediately, or wrapped in 6mm plastic. To allow a tree to succumb to pine beetle infestation would guarantee the growth of even more beetles that would eventually emerge from the tree and infect neighboring trees. 
  • Clear out all felled and dead trees from the property. The beetles can still complete their life cycle in trees that have died.
  • Trees with light infestation might be saved if treated with insecticide. Insecticide can also be used to protect trees that have not yet been affected by pine beetles. Carbaryl, permethrin, and bifenthrin, known by their brand names as Sevin, SL, Astro and Onyx, respectively, are labeled for use on mountain pine beetles. Homeowners should be warned that these chemicals are dangerous and can potentially contaminate water supplies and kill benign wildlife, such as bees and fish.
  • Walk the property and assess the general health of your trees. Homeowners who learn to identify tree species will know where to concentrate their observations.
  • Replace lost trees with trees that are not susceptible to bark beetles. 
In summary, pine beetles are a threat to homeowners who live in certain regions.