Bark beetles in California include western pine beetles on ponderosa pine; mountain pine beetles on lodgepole and sugar pines; and engraver beetles on Monterey, pinyon, and other pines. Trees already stressed by drought, disease, or mechanical damage are most likely to suffer. Insecticide sprays can’t save infested trees: remove infested trees and protect healthy ones.
Identifying bark beetles and their damage.
Adults are small, dark, cylindrical insects about the size of a grain of rice; they can fly from tree to tree. Larvae are tiny grubs that feed beneath bark on branches and trunks. Infested trunks and branches have many tiny holes where beetles have bored in or emerged. Tree sap or dust from boring can exude from holes. If you peel back bark on infested trees, you’ll see galleries, or tunnels, from adult or larval mining.
Bark beetles injure trees by disrupting the flow of nutrients.
Adults and larvae feed in the area of the inner bark that transports food through the tree. Infested trees can die in one season, causing limb drop and fire hazards.
Keep trees vigorous to reduce attacks.
Healthy trees defend themselves by releasing sap into holes before adult beetles can lay eggs. Drought, disease, and injuries reduce a tree’s ability to combat invasions. When possible, properly irrigate drought-stressed trees. Thin groups of trees or stands to keep remaining trees vigorous. Dense stands favor beetle attack. Avoid compacting soil and injuring roots and trunks during activities such as construction. Diversify your landscape. Avoid single-species stands.
Remove severely infested trees.
Inspect your trees for signs of bark beetle invasions. Remove infested trees and destroy infested material by chipping or solarizing to prevent emerging beetles from attacking healthy trees. Solarize infested wood by tightly wrapping small piles in thick (10 mil) clear plastic and leaving them in the sun for several months.
Insecticides aren’t recommended
Insecticides, including systemics, won’t control insects already inside the tree. Confine chemical use to protecting healthy specimen trees and integrate with other methods to improve defense.