University of Maryland Extension

Bark Beetles

Back to Common Problems of Trees and Shrubs

elm gallery
Evidence of bark beetle activity

Bark beetles are very small insects, usually less than 8mm. They are brown to black in color and cylindrical in shape. The beetles generally attack shrubs that are stressed or weakened. Often several beetle species will attack and individual plant.

Bark Beetles on needled evergreens

Needle color will turn from bright green to light green, then to yellow and finally to reddish brown. The initial signs of attack are pitch tubes and/or boring dust. The pitch tubes are small masses of pitch (sap), which are usually whitish in color and often mixed with reddish boring dust or frass.

Borers that attack evergreen trees and shrubs are primarily long-horned beetles (round headed borers), such as the southern pine sawyer. These beetles are much larger than the bark beetles (an inch or more with long antennae). They are stress pests and generally attack stressed plants. Symptoms include branch dieback due to feeding damage, and exit holes. Exit holes of long horned beetles are oval and about 1/4 inch or larger in diameter.

yellow pine
Initial symptoms are fading and yellowing of needles

pitch tubes
The pitch tubes are small masses of pitch (sap),
which are usually whitish in color and often
mixed with reddish boring dust or frass

southern pine sawyer
Southern pine sawyer adult

southern pine sawyer damage
Southern pine sawyer damage

mugo pine dieback
Damage on mugo pine
 

Bark beetles on deciduous trees 

The beetles generally attack stressed or weakened trees (oak, elm, birch, ash, hickory, hackberry, beech, sweetgum, maple cherry, pear, etc.). The immature beetles construct galleries as they feed on the cambium, under the bark. Healthy trees can usually withstand bark beetle attacks by literally trapping the beetles in a sticky flow of pitch. Bark beetles emit a chemical signal, or aggregation pheromone, which attracts more bark beetles to the tree under attack. Beetles often carry pathogenic fungi such as Dutch elm disease and oak wilt, which are deposited in the vascular system of the tree. These fungi quickly multiply and clog the water conducting vessels of the tree which hastens its death.

Management

The best control for bark beetles and borers is prevention. Healthy plants are able to withstand most bark beetle attacks. Insecticidal sprays will not kill the beetles or larvae inside the shrubs and sprays will not reverse the damage that has already occurred. Plants should receive adequate water in times of summer drought. Dead or dying shrubs should be removed to eliminate breeding sites for additional beetle generations.

Additonal Resource

(PDF) HG1 Conifer Bark Beetles

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