Key Features
- Decline and dieback of canopy
- Small holes in trunk, sawdust
- Wasp-like moth (with clear wings)
Symptoms
Injured trunks or branches have loose or pealing bark. Sawdust-like excrement can be seen from holes where borers have attacked portions of the tree that are above ground. Caterpillars beneath the bark are usually creamy white in color. When adults emerge from the trunk, the brown straw-colored skin of the transitional stage known as a pupa is left hanging out of the trunk, or branch. Borers that attack at the tree base or just below the soil line may have excrement pellets and pupal skins hidden from view. Infested trees have dead limbs or twigs. The clear wings, slender bodies and flight habits of adult moths in this group cause them to superficially resemble wasps. Unlike wasps, adult moths lack chewing mouth parts and have bodies that are covered with scales. Adult moths have straw like mouth parts that are used for sucking nectar. Clearwing borers are found on many species of trees.
Biology
Late instar caterpillars spend the winter beneath the bark of infested trees. Larvae turn into a transitional stage called pupae in the tree bark before they become adults. Just prior to emergence, the pupa pushes its way out of the bark. When the adult emerges from the pupae it leaves the pupal skin in the branch or trunk. Soon after females emerge, they crawl a short distance on the bark, arch their abdomen and release a scent into the wind. This scent helps the female find a mate by attracting males who are down wind. After mating, eggs are laid on the bark. Eggs hatch into caterpillars that chew a hole in the bark. Depending on species, moths can have 1-2 generations a year. Oak borers take 2 years to develop into an adult.
Management Recommendations
Reduce water stress to prevent borer injury. Be sure plants receive at least 1" of rain or water per week. Avoid mechanical injury to trees during the mowing season. Improper use of plastic trunk wraps can make trees more susceptible to clearwing borers that attack tree trunks. Tightly coiled wraps keep bark moist, and can protect borers from parasitic wasps that normally attack them through the bark surface. Loosely coiled plastic wraps with at least 1/4 inch of air space do not cause this problem.If borers have been found, apply a long lasting insecticide (bifenthrin, permethrin, or chlorantraniliprole) to the trunk and branches at the beginning of the flight period listed in the links section.
Effective Pesticides
Active Ingredients include: Bifenthrin, Chlorantraniliprole, Cyantraniliprole, Lambda- cyhalothrin, Permethrin
Resources
