Types of Bark Beetles
There are more than 600 species of bark beetles in the U.S., including 200 in California. California now has 20 invasive species of bark beetles, of which 10 species have been discovered since 2002. Bark beetle adults are small, cylindrical, hard-bodied insects about the size of a grain of rice. Most species are dark red, brown, or black. Additional information to help you identify bark beetles can be found here: Bark Beetles in California Conifers
Life Cycle of Bark Beetles
Bark beetles are attracted to trees that are stressed, diseased or injured. Adult beetles bore holes into the tree to deposit their eggs under the tree’s bark. When eggs hatch, the larvae feed briefly on the inner bark. They then continue to tunnel inward. The larvae become adult bark beetles and renew the cycle. Once beetles successfully attack a tree, it releases pheromones which attract other beetles to the tree, concentrating the attack and making it difficult for the affected tree to fend them off. Beetles are most active in the summer and warm spring and fall days.
A tree’s only defense against bark beetles is sap (pitch), which is produced by a healthy tree. The sap pushes bark beetles out, keeping them from being able to deposit eggs and kill the tree. But when a tree is diseased or stressed by drought, it may not be able to produce enough sap to protect it from being overrun by beetles. When bark beetles’ population is at epidemic levels they can still attack and overcome even healthy trees.