Insects that bore into trees
Insects that drink sap and eat plant parts typically attack the leaves or fleshy portion of the tree, which generally does not kill the plant. Boring insects, on the other hand, bore into the main truck or side branches, causing much more serious damage such as branch dieback, structural weakness or decline and death of the plant.
Some insects will bore into healthy trees, but in many cases, the borers are attracted to weak ones. Insects that only bore into weakened trees are known as “secondary attackers,” because they strike trees that have been weakened by another stress. When borers attack trees, they normally leave behind telltale signs such as holes in the tree, patches of resin, gummy substances exuding from the bark, sawdust or waste products, commonly known as “frass.”
Here are some insect borers that are of local concern:
Walnut twig beetle: The walnut twig beetle is an insect native to the Southwest. This insect bores into the branches of Western walnuts. This tunneling activity does not do much harm to the walnut. The harmful part of this feeding activity is that the twig beetle can carry the fungal spores of thousand canker disease. Thousand canker disease has impacted walnuts in the West since the 1980s, and may eventually cause the death of the host walnut tree. This disease complex was confined to the West until 2010, when it was observed in some black walnuts growing in Tennessee. Following this observation, most states have been monitoring for the presence of walnut twig beetle or the fungus that causes the disease. In 2013, walnut twig beetles were trapped in Cecil County; in 2014, the fungus was identified growing in one of the impacted walnut trees. Cecil County is now under quarantine for walnuts.
Article by Mike Kay, Frederick County Forestry Board