What Is It?
This beetle (Agrilus anxius), native to North America, is 7-11 mm in length and dark green-bronze in color.
What's the Problem?
This insect is often considered a secondary pest that attacks birch trees already stressed by things like drought. If populations build high enough on stressed trees, however, the beetle may move on to attack healthy trees.
Attacks result in progressive dieback of the crown and death of the tree within a few years. Injury is caused by the larvae feeding under the bark.
What Can I Do?
A healthy birch tree is most resistant to borer attack. Proper and frequent tree care including watering should be maintained.
If a tree exhibits top dieback symptoms, dead branches should be pruned out in the fall 30-50 cm below the dead wood or any signs of successful beetle attack (D-shaped emergence holes). All pruned material should be destroyed to prevent any beetle emergence the following spring.