What is a Bark Beetle?
In the western U.S., bark beetles are the most destructive insects in conifer forests. Hundreds of different species of bark beetles can be found in the Rocky Mountain region as well as California. Bark beetle attacks wreak havoc on healthy trees, causing them to die in a short period of time.
Where are Bark Beetles Found?
Bark beetles can be found all over the world. In the United States, conifer forests are experiencing particularly bad outbreaks, resulting in swaths of dead trees and threatening forest health. According to the U.S. Forest Service, in Colorado and Wyoming alone, spruce beetles and mountain pine beetles (also called Dendroctonus ponderosae or MPB), have impacted more than 4 million acres. These beetles tend to develop in several species of trees, including lodgepole pines as well as Scotch, limber, and ponderosa pines and spruce trees.
Bark Beetle Life Cycle
Mature bark beetles are small, hard-bodied insects that are about the size of a grain of rice. Most are red, brown, or black in color. The adult beetles bore holes into trees to lay their eggs under the bark. When the eggs hatch, the larvae feed on the tree’s inner bark or phloem. The small, white grubs then continue to tunnel inward, eventually killing the sapwood. When beetles successfully attack trees, chemicals called pheromones are released that attract more beetles, strengthening the attack. Bark beetles only leave the tree when they become adults and fly to another tree to lay their eggs and continue the cycle.
Signs of Bark Beetle Infestation
Host trees will begin to turn from green to yellow to reddish brown at the crown anywhere from a month to two years from the initial attack. This is an indication of a dying tree. Inspection of the bark may show small globules of resin called pitch tubes, small exit holes throughout the bark, and reddish boring dust in the bark’s crevices or at the base of the tree trunk. Bark removal will reveal bark beetle galleries where the eggs and larvae exist in the tree.
Bark beetles prefer to prey on trees that are weakened by drought or other unfavorable conditions, but when bark beetle populations are high, they will attack healthy trees as well. A tree’s only defense against bark beetle outbreaks is to produce sap, or pitch, which pushes the beetles out, preventing tree mortality. If the tree is unable to produce enough pitch, it cannot fend off the attack.
Bark Beetle Management
Unfortunately, large bark beetle outbreaks are very difficult to manage. The best way to prevent them is by thinning overly dense stands of trees to promote tree age and vigor and to reduce competition. Small outbreaks can often be controlled by immediately removing infested trees. Preventative insecticide sprays can also be applied to reduce the likelihood of an attack. Pheromone packets containing verbenone are sometimes used to disrupt the attraction of incoming beetles.
The bark beetle epidemic continues to threaten the economy and natural resources of the western United States. Concerned about bark beetles? Integrated Lawn Care can help. To learn about how to protect your trees, contact us today.