WOOD BORING BEETLES IN TREES

James R. Baker, Extension Entomologist Emeritus

Five kinds of wood boring beetles infest trees and shrubs in North Carolina: roundheaded wood borers, flatheaded wood borers, weevil grubs, ambrosia beetles and bark beetles such as the southern pine beetle. Many common wood borers are the roundheaded and flatheaded borers. The azalea stem borer, carpenterworm, locust borer, southern pine beetle, granulate ambrosia beetle and the whitepine weevil are discussed in more detail in Ornamental and Turf Insect Notes on trees. It should be noted that many of these borers are secondary invaders of trees that are dying or dead.

Roundheaded Wood Borers

 The adults are called longhorned beetles because of their long antennae. Body length varies from 1/4 to almost 3 inches. The larvae have no noticeable legs and are white or yellowish and are usually slender. Beetles emerge from infested trees from late spring to early fall. After mating, females seek egg laying sites, often under bark scales, in crevices or in wounds of trees under stress or in poor health. Some of the longhorned beetles chew elliptical niches in the bark to lay eggs. After hatching, the larvae of some species may feed beneath the bark in the cambium region for a time before entering the wood. Other species do not bore into the wood but remain under the

bark. Life cycles of the different species vary from several months to 2 or 3 years.
 

Flatheaded Borers

 Beetles emerge from most trees in the early spring and summer and lay eggs around cracks and wounds. After hatching, the larvae bore first in the cambium region beneath the bark and then enter the heartwood. Their elliptical tunnels are long and winding and are packed with fine borings arranged in concentric layers so that arc-like bands appear when the galleries are exposed. Most species complete their life cycle in a year, but some require 2 to 3 years. Dark, dead areas of bark, often with sap exuding, result from their burrowing. Tunnels made by the larvae do not have outside exit holes, although the sawdust-like frass may be visible in cracks in the bark or where the bark sloughs from the trees.

 Borers are particularly damaging to newly transplanted trees and those weakened by various causes such as drought, sunscald of the bark, mechanical damage, ice storms, and fire damage. Diseases, frost damage, pesticide injury or defoliation by leaf feeding insects can weaken trees. Filling, excavating or compacting soil beneath trees can hurt their health. Installation of utility pipes and lines may also damage roots.

 Since weakened trees are more susceptible to borer attack, the best way to avoid borers is to keep trees in good health. Provide plenty of water during drought periods. Have the soil analyzed and apply the correct kind and amount of soil amendments. Try not to injure roots or above ground parts of plants. Remove and destroy dead wood and prune during the winter months for most trees (prune peach and apricot trees in spring). Choose trees suited to your growing area. Where possible, select varieties less susceptible to borer attack. Newly transplanted trees with thin bark should have the trunks wrapped for a year or more with burlap or other material (wrapping prevents egg-laying of many borers and reduces injury from sunscald).

 To prevent borer infestation, use one of the following pesticides and follow label directions carefully. Do not apply to wet bark. Note that the pesticides Dursban and Lindane are no longer available for use around homes. Imidiacloprid products are being commonly used for flatheaded borers.  This is a systemic and not just a protective bark spray.  See the NC Agr. Chem. Manual for more pesticide choices and here for a partial list of homeowner sprays.

 ENT/ort-26  April 1994 (Revised)

Web page last reviewed January, 2011 by the webperson.