The mountain pine meetle (MPB) is a small insect that has had a major impact on forests throughout Colorado. Although it is only about the size of a grain of rice, the MPB can kill large numbers of pine trees during population outbreaks. This beetle is native to western North America and normally plays an important role in forest ecology by helping remove older or weakened trees. However, in recent decades, unusually large outbreaks have killed millions of acres of forest across Colorado and other parts of the Rocky Mountains.
MPB mainly attack species such as lodgepole pine and ponderosa pine. Adult beetles begin an attack by boring through the outer bark of a tree and tunneling into the inner layer known as the phloem. This layer carries nutrients throughout the tree. Female beetles lay eggs inside these tunnels, and when the larvae hatch, they feed on the phloem, creating winding galleries beneath the bark. As they feed, the beetles also introduce a fungus known as blue-stain fungus. This fungus interferes with the tree’s ability to move water and nutrients, which weakens the tree even further. Together, the feeding damage and fungal infection usually kill the tree within about a year.
A key sign of an active infestation is the presence of pitch tubes on the outside of the bark. Pitch tubes are small blobs of sticky sap that form when the tree attempts to defend itself against invading beetles. The tree pushes sap toward the entry holes to trap or force the beetles out. These pitch tubes are usually white, pink, or reddish-brown and resemble small clumps of popcorn or hardened sap attached to the bark. When pitch tubes appear fresh and numerous, it often indicates that beetles are actively attacking the tree.
Managing infested wood is also important when trying to slow the spread of beetles. When infected trees are cut down, the freshly cut trunks should be chipped, fully removed from the location, or tightly wrapped in clear plastic and left sealed for at least one year. The plastic traps heat from the sun, creating temperatures high enough to kill developing beetles living under the bark. By preventing the insects from emerging and spreading to nearby trees, this method can help limit the spread of infestations in forests or residential areas.
People can also take steps to help protect healthy trees before beetles arrive. One common method is spraying preventive insecticides on the trunk of high-value trees before the beetles begin flying and searching for new hosts in the summer. However, these treatments must be applied by a certified pesticide applicator, since specialized equipment and training are required to apply the chemicals safely and effectively. Another strategy involves placing pheromone patches on or near trees. These patches release chemicals that disrupt the beetles’ natural communication signals, helping repel them or reduce the likelihood of a mass attack. Monitoring trees regularly and acting early can make a big difference. Getting ahead of an outbreak helps protect healthy trees and can reduce long-term damage to forests and communities.
