The carpenter bees have been especially active this year. I have a wooden structure over my back door, and there is sawdust on the walk daily. I know their eggs winter over in the holes and emerge in the spring. I'm not into killing -- but -- is there any other way?
The only way to tackle them without using any pesticides is to plug the hole and recoat the wood surface with paint or stain just when they first emerge in spring (it takes a while for them to mate and start laying eggs again.) That window of opportunity has passed.
The longer you wait to address the problem, the more bees will potentially be killed because more eggs will be in the tunnels and you will eventually need to address it. Looked at that way, the sooner the better. Here is our website info about carpenter bees: http://extension.umd.edu/hgic/carpenter-bees You can use a spray or a dust.