Pine Trees and Beetles


Many beetles are associated with pine trees; however the most well-known are the bark beetles. Pine bark beetles require a pine tree to complete their life cycle. Some pine bark beetles are considered pests due to their ability to kill healthy trees. Many pine bark beetles are not pests, however, and only use trees that are unhealthy.


All pine bark beetles function in the same general way. They require a pine tree as a host in which to lay eggs and for their development into an adult beetle. Most beetles only use unhealthy trees in which to develop and, in doing so, contribute to the decline of the tree. Sometimes a tree will recover, but other times the tree will die. The loss of the unhealthy tree frees resources such as water, nutrients and sunlight for other healthy trees to use.


Adult pine bark beetles chew into the bark of a tree to mate and forming chambers in which to lay eggs. When the eggs hatch, the larval, grub-like beetles feed on the tree tissues under the bark that transport water and nutrients. These tissues are severed and in some cases this happens around the entire circumference of the tree so that no water and nutrient movement can occur. Additionally, many bark beetle carry fungi that will clog up these tissues, which accelerates tree decline. This often leads to tree death.


As with many insect and plant associations, bark beetle species are associated with specific pine tree species. In the southeastern U.S., bark beetles, such as the southern pine beetle and five-spined ips beetles, attack pine such as loblolly, Virginia and white pine. In the western U.S., beetles, such as the mountain pine beetle, also attack numerous pines such as lodgepole, ponderosa and sugar pines.


On individual trees in situations such as home landscapes, insecticide sprays can be used to reduce the number of beetles invading a tree. In a forested situation, sprays are often too costly and time consuming due to the number of trees requiring treatment. During severe bark beetle outbreaks, buffer areas consisting of wide areas of trees completely cut down are created in front of the beetle advancement in hopes of stopping them. In many home landscape situations, trees showing signs of beetle attack are under stress from other causes and are not the primary reason for decline.


Several misconceptions surround the bark beetles that attack pine trees. The tiny holes found in the bark of pine trees are usually thought to be entry holes for the beetles. Those holes are formed by the numerous emerging adults that have completed their development that started as an egg. Another misconception is that bark beetles crawl from one tree to the next. Bark beetles are often capable of flying several miles. Finally, it is claimed that bark beetles can often be heard chewing inside pine trees. Much larger beetles called pine sawyers are what is often heard chewing under the bark of pine trees.

Keywords: Pine trees, Beetles, Insects