Bark beetles are common tree pests that can damage and kill trees. They are most damaging to pines and other conifers, especially those already stressed by drought, disease or damage. Signs of infestation include small holes in bark where beetles have bored in or emerged, galleries under the bark, and tree sap or dust coming from holes. To reduce bark beetle attacks, keep trees healthy through proper care like irrigation, thinning dense stands, and avoiding injuries to bark and roots. Remove severely infested trees and protect healthy trees through good cultural practices rather than insecticide use, as chemicals cannot save infested trees.

1. Bark beetles are common pests of many
trees. Some of the most damaging attacks
occur to pines and other conifers. Trees already
stressed by drought, disease, or mechanical damage
are most likely to suffer. Insecticide sprays can’t save
infested trees. Instead, promptly remove infested trees
and protect healthy ones with proper cultural care.
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 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.
Shothole borer is common on broadleaf trees.
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.
✦ Needles turn yellow and drop off infested trees.
✦ 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.
BBaarrkk BBeeeettlleess
University of California
Statewide Integrated Pest
Management Program
Remove severely infested trees.
✦ Regularly inspect your trees for signs of bark
beetle invasions including dust from boring, small
holes exuding sap, and tree decline.
✦ Promptly 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.
✦ Protect healthy trees through good cultural care.
Insecticides generally aren’t recommended.
✦ Chemicals can’t save infested trees.
✦ Insecticides, including systemics, won’t control
insects already inside the tree.
✦ Chemicals aren’t effective unless applied before
adults land on the tree.
✦ Confine chemical use to protecting healthy
specimen trees and integrate with other methods
to improve defense.
✦ Effective insecticides are available only to licensed
applicators.
Minimize the use of pesticides that pollute our
waterways. Use nonchemical alternatives or less
toxic pesticide products whenever possible. Read
product labels carefully and follow instructions
on proper use, storage, and disposal.
For more information about managing pests, contact your
University of California Cooperative Extension office
listed under the county government pages of your phone book
or visit the UC IPM Web site at www.ipm.ucdavis.edu.
See Pest Notes: Bark Beetles
at www.ipm.ucdavis.edu for more details.
What you use in your landscape
affects our rivers and oceans!
University of California
Statewide IPM Program Cooperative Extension March 2012
Larval galleries of
European elm bark beetle.
Ips bark beetle (actual
size 1⁄8 to 3⁄8 inch long)
Engraver beetle holes
and sap.