Injury is due to larval feeding tunnels under the bark which girdle the trunk or branch of the tree. Generally, the most susceptible trees are those weakened by disease, age, defoliation, adverse weather conditions, or previous borer infestations. Healthy, young trees are rarely attacked. Infestations and dieback usually start at the top of the tree and work downward. Infested branches often are somewhat swollen and brown, with ridges appearing around the smaller ones.
Branches die because of the girdling effect of the larval feeding tunnels.
They are also packed with sawdust left over from feeding. External signs of these hidden feeding tunnels are conspicuous scarred areas or zigzag ridges caused by the healing process in infested trees. In early spring, when tree sap begins to flow, overwintering larvae begin to feed and migrate close to the surface of the bark. Adult emergence in Missouri is typically in late spring and lasts for six weeks. Newly hatched larvae then bore into the bark and begin feeding.