Bark beetles

Bark beetles get their name from tunneling in the wood of woody trees and shrubs just below the bark. Generally they are small beetles only 1/16 to ¼ inch. Bark and twig beetles are most apt to be found in stressed or dying plants but some species may attack healthy trees. Dead and dying branches in an otherwise healthy plant may also be attached. In addition to disrupting the plant’s vascular tissue a more serious threat to the plant can be the introduction of a vascular disease by pathogen-infested beetles. Dutch elm disease is a serious disease of many elms that find entry into trees this way. Oak wilt is also suspected of being transmitted similarly by bark beetles.

Exit holes in the bark where adult beetles have emerged often accompanied with sawdust generally indicate the presence of bark beetles. In advanced stages, dead and/or loose areas of bark may be seen.

Some common bark beetles include the shothole borer (common on fruit trees), the ips beetle, elm bark beetles, ash bark beetle, pine and spruce beetles, and ambrosia beetles (a wide host range.)

Control of Bark Beetles:

Since dead and dying branches on otherwise healthy plants can provide an entry point for beetles, prune out these branches on a regular basis. Burn or otherwise dispose of prunings as beetles can complete their lifecycle in the cut branches and move on to infest new trees.

Maintain good plant vigor. Water trees during periods of drought and fertilize if the plant’s growth rate is substandard. Monitor newly planted trees closely as slow establishment can make plants more vulnerable to attack. Adult beetles are attracted to stressed trees where they lay their eggs on the bark. The eggs hatch and the young larvae tunnel into the bark. Once inside the tree they cannot generally be killed by pesticides. To be effective pesticide must be applied to the trunk of the plant to kill the emerging young before they tunnel into the bark.

In the case of serious diseases such as Dutch elm disease and oak wilt, prompt removal of diseases trees before the beetles emerge and spread the disease is necessary. See information on these diseases for further recommendations.

Other images

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What appears to be shotholes in the bark of this red cedar (Juniperus virginiana) are in reality the emergence holes of bark beetles (Coleoptera)
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The exit holes of bark beetles (Coleoptera) in red cedar (Juniperus virginiana) are so numerous they resemble shotholes from a shotgun blast
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