Dusky Birch Sawfly
Q: My small ‘Whitespire’ Japanese birch has been defoliated each fall for about the past three years. No permanent harm because it comes right back every spring. I just found these hungry little guys on it and wonder if they are butterflies or moths to be because of their close proximity to my butterfly bushes.
A: They are the larvae of neither butterfly nor moth. They are the children of the dusky birch sawfly, a wasp-like insect.
Since they are not caterpillars, products containing Bacillus thuringiensis won’t kill them.
The contact insecticide carbaryl (click for sources) offers good control if sprayed on the entire tree. Imidacloprid (click for sources) is a systemic insecticide which can be applied to the soil around the tree before feeding activity is noticed.