This meek little fella is used as one of our most frequent scapegoats.
Scapegoat for what? Our inability to water our birch Trees properly. Nothing better
than having a bug to blame, especially if they can't defend themselves. The literature is full of quotes like this, "The borers' effects on mature Trees under STRESS that can be devastating". Key words, under stress. Another, "Drought conditions coupled with high temperatures lead to crown die-back and subsequent susceptibility to borer attack".
During my climbing career, I climbed and pruned many birch Trees, especially our favorite, the Cut Leaf Weeping Birch, CLWB. I have never once seen borer activity in healthy Trees. Show me a water-stressed, limp-looking, crown-full-of-deadwood CLWB and I may be able to show you some BBB.
The borer's life cycle goes like this. Adults emerge in late June and live approximately 3 weeks. They are about .5 inches long and have a metallic bronze appearance. Eggs are laid in the bark of weak or dying branches. The eggs hatch in two weeks and go through five metamorphoses, (instars) happily munching weakened birch tissue the while. Content, they overwinter as pupae to complete the cycle.
Birch Trees have the highest water requirements of any Tree planted in Calgary. Calgary is not a environment where any birch tree would choose to grow. The closest we come are two very tough birch shrubs.
If you love this Tree, love this Tree, water it.
If you do you will never see this insect.
See my article, Watering Calgary Trees.
(Photo credit: “bronze birch borer (Agrilus anxius)" by Whitney Cranshaw, Colorado State University, Bugwood.org, licensed under CC BY 3.0 US.)