What Is The Mountain Pine Beetle?
The mountain pine beetle (MPB) Dendroctonus ponderosae, is a species of bark beetle native to the forests of western North America from Mexico to central British Columbia. It has a hard black exoskeleton, and measures about 5 mm, about the size of a grain of rice.
Mountain pine beetles inhabit ponderosa, lodgepole, Scotch and limber pine trees. Normally, these insects play an important role in the life of a forest, attacking old or weakened trees, and speeding development of a younger forest. However, unusual hot, dry summers and mild winters in Montana during the last few years, along with forests filled with mature lodgepole pine, have led to an unprecedented epidemic.
What Does It Do?
The beetles swarm individual trees in a coordinated mass attack. They release pheromones (natural beetle attractants) to bring in even more beetles. When the tree is full they release a different pheromone to tell the rest of the beetles to pick another tree. In historic infestations, entire mountainsides would be killed. Today, entire forests and entire mountain ranges are being attacked and killed.
Healthy trees can repel the attack by pushing the boring beetles from their holes with sap. Mature trees are the main targets of the bark beetles because the younger trees rapid growth allows efficient production of sap.
The beetles feed on the thin cambium layer between the bark and the sapwood. (This is the part of the tree that grows and carries water and nutrients from the roots to the leaves and energy from photosynthesis to the roots.) The boring beetles quickly girdle the attacked tree; their feeding destroys the conduits for water and nutrients, and it the tree dies. It difficult to tell which trees have been attacked until the year after their death because the needles stay on the tree and stay green for quite some time - like a fresh cut Christmas tree. The year after the tree is killed it turns the characteristic bright red color. Then within another year or two, all of the needles fall off of the tree and it turns a desolate gray.
What Is Being Done To Thwart Attacks?
The long-term remedy is to thin susceptible stands of trees, leaving well-spaced, healthy trees. The U.S. Forest Service recommends salvage logging, followed by prescribed burning, as a solution for preventing further beetle spread and wildfires. Bad Beetle follows salvage logging practices in Montana.