Why Do Pine Beetles Attack Old Trees?

Mountain Pine Beetle

• The mountain pine beetle has also been called the Black Hills beetle or the Rocky Mountain pine beetle. The beetles most commonly attack and kill ponderosa, lodgepole, limber and Scotch pines. Bristlecone and pinyon pine are less susceptible. While damage is most dramatic in places like South Dakota's Black Hills or Colorado's Rocky Mountain National Park, infested firewood can endanger landscape trees many miles from the mountains.

Southern Pine Beetle

• The southern pine beetle infests forests in the eastern and southern areas of the U.S. New Jersey has the most extensive damage -- southern pine beetles are killing 14,000 acres of forest there every year. The southern pine beetle attacks shortleaf, loblolly, Virginia and pitch pines most often. When an infestation is rampant, however, no pine tree is safe.

Susceptible Trees

• During the early stages of an infestation, the beetles attack older trees. Trees that have been weakened by drought, fire, overcrowding or other types of stress are also prime targets for these voracious beetles.

  Even majestic, century-old lodgepole pines -- once thought to be safe because the cold temperatures at higher elevations often kills the beetles -- are dying in droves (see References 2).

  Spraying can be challenging since the beetles often attack very tall, old trees. Chemical applicators need high pressure and specialized equipment to save mature trees. (See References 5)

Symptoms

• Trees that have been killed by pine beetles have rusty, reddish-brown needles that eventually fall off. Other signs of infestation include patches of white resin on the trunk, called pitch tubes, as well as sawdust at the base of the tree. Evidence of woodpeckers feeding on the trunk, blue-stained sapwood and live beetle larvae, eggs or mature adults also signal a significant infestation.

Long-Term Impact

• Dead, dry trees increase the danger of forest fires in an area. Water quality also suffers. Without tree roots to hold soil in place, streams and reservoirs can become clogged with sediment.

  Outdoor tourism suffers because campers, skiers and hikers find the dead landscapes to be less of a draw. Dead trees can also be dangerous for hikers as they can topple over in windstorms.