• The word "borers" applies to all wood-boring insects, including moths, beetles, sawflies, horntails and flies. Most of the damage is done when they are in the larval stage.
• Borers attack urban and rural forest trees, causing wood defects and weakening the tree.

• Dead tree, dead top of tree, dead limbs or branches, or branches that lack vigor.
• Exit holes, where the insect has left the tree, that range in size from a pinhead to 3/4".
• Sawdust at the entrance of exit holes, or on the ground beneath.

• Adult boring insects deposit their eggs beneath the bark by piercing or chewing through it.
• Once hatched, the larvae feed by tunneling through young shoots, branches, trunks, or roots.

• They kill trees, both old trees and young trees.
• Loss of terminals, branches and trunks weakens and deforms the entire tree.
• In municipal settings, trees with borers become hazardous when their wood is weakened.

• Trees suffering from environmental stress such as prolonged drought or site that is not suited to the species.
• Storm-damaged trees: their weak condition and open wounds are inviting to insect borers.
• Transplanted trees, especially when not watered the first year or two.
• Young nursery plantings growing near infested areas.
• Common examples include white birch, European mountain ash, crabapple, and black locust.

• Plant the right tree in the right location in the first place.
• Minimize environmental stress, especially on young trees (e.g., with summer watering).
• Get a positive identification. There are many different species of insect borers, and each one has a different life cycle, therefore requiring different timing on treatments.
• Remove dead or damaged wood, and be sure pruning cuts are made properly.
• For details on treatments, consult a current Cornell Recommends: Trees & Shrubs.

Warren T. Johnson and Howard H. Lyon, 1991. Insects that Feed on Trees and Shrubs. 2nd edition, revised. Ithaca: Cornell University Press. If you want to consult this reference book for a discussion of a particular species, or to get other information on this and related insect topics, call your regional DEC or Cooperative Extension, or us directly at the Community Forestry Education Project, 716-461-1000.