Larvae: Larvae hatch from eggs on birch leaves. The larvae are white and flat with a black head. After 10 to 15 days, they are 6 mm in length and will cut a hole in the leaf and drop to the ground, where they pupate.
Adult: After 2 to 3 weeks, adults emerge as black, wasp-like insects and climb back up the tree to lay more eggs on birch leaves. This cycle may occur up to 4 times over the summer.
Leaf holes: As larvae “mine” and eat the tissues inside the leaf surfaces, they leave small holes. These holes soon join together to form a single large, hollowed-out blotch on the leaf where the larvae can drop to the ground.
Healthy birch trees can resist this damage; therefore, regularly water, fertilize and prune your birch trees.