How storm damage can lead to wood-boring insect pests

As summer storms roll through they often damage our trees by snapping limbs, breaking them in half, and uprooting them. When trees are damaged by high winds, hail, or even lightning they become weakened and stressed. Stress and wounding induce trees to produce airborne chemicals that signal they are distressed. Unluckily for trees, certain insects have adapted to detect these chemicals and use them to their advantage. Stressed plants are easier to infest since their defenses are already compromised, so female insects looking for egg-laying sites will head towards these storm-damaged plants. Two of the most commonly found groups of insects performing this behavior are the wood-boring beetles and clear wing moths.

Wood-boring beetles most often are either round-headed borers or flathead borers. Roundheaded borers have larvae that are canister shaped and that mature into longhorn beetles as adults. Some famous examples would include the cottonwood borer, pine sawyers, and poplar borers. Roundheaded borers are part of the natural cycle of decomposition and feed on dead and dying trees. Many people find them in their firewood or in stacks of unprocessed wood. When the beetle exits the tree they leave a circular hole in the bark. On the other hand are the flathead borers which are flattened in appearance (sort of like a tapeworm) and mature into metallic wood-boring beetles. Some famous examples would be bronze birch borer, flatheaded apple tree borer, and the emerald ash borer. These insects cause a “D” shaped exit hole in wood.  Most of the time flathead borers do not cause serious damage to trees but species like the emerald ash borer can induce tree mortality.

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An adult cottonwood borer

Clearwing moths are pests as caterpillars, during this life stage they live under the bark and feed on the tree often causing extensive damage. As adults they are wasp mimic, their wings are see through and most are colored black and yellow to mimic stinging insects such as yellowjackets. When these moths emerge from trees they leave behind their pupal case which looks like an orange, papery cigar. Some notorious example of clearwing moths are the lilac-ash borer and the peachtree borer.

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Pupal skins sticking out of a tree infested with clearwing moths

Since most of the beetles are not harming healthy trees, management is not required. Proper maintenance and care of trees will lead to higher health and fewer run-ins with beetle borers. Clearwing moths on the other hand can cause damage to trees we would like to see stick around. To prevent pest problems with these moths, an application of a pyrethroid insecticide to the lower trunk will control egg laying females. Timing of this application varies by tree species and location. You should consult your local extension service’s materials on clearwing moths for more precise information.


Photos courtesy of Jim Kalisch; UNL Entomology Department


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