Adult bronze birch borers are olive to bronze-colored beetles approximately 1/2″ long. They lay their eggs in bark cracks or under flaps of bark. The larvae bore into the branches or trunk after hatching and bore winding galleries along the cambial layer (between the wood and the bark). The larvae grow to about 1″ long and are creamy to white in color with a head wider than the body. The galleries may heal with swelling showing on the outside of the tree (lumpy bark), or may girdle and kill branches or trunks. Leaves may be yellow (chlorotic) as a result. The adults may feed on leaves, but cause little damage. Bronze birch borers attack trees weakened by age, environmental stresses, or previous insect attacks.

Select non-chemical management options as your first choice!

• Woodpeckers and parasites are important controls of bronze birch borers in rural areas. Keep trees healthy. Vigorous trees are much less susceptible to borer attack. Prune out dying branches. Prevent injury and insect damage. Chemical controls are in the early spring and often ineffective once severe damage has occurred  Signs and symptoms of BBB damage are easier to detect than the actual insects, which spend most of their lives inside the tree. Wilted leaves near the tree’s top are often the first identifiable sign of BBB, followed by twig and branch dieback. Larval development takes 1 to 2 years, depending on the climate (temperature, humidity, drought, etc.) and the length of the growing season. After growing to about one inch in length, larvae pupate inside the tree. Adults emerge from the tree, leaving a hole in the tree like a sideways capital “D”. Adults feed on birch leaves. Because the adult stage only lasts a few weeks, little damage is caused by adult feeding. The D-shaped exit hole made by the adult emerging from the tree is a sign of BBB infestation.