The carpenter bees are doing a number to my deck and wheelchair ramp. This has been going on for a few years. I have tried spraying the wood and the burrows with all kinds of nasty chemicals like for carpenter ants with very little effect. I've tried treating the wood and the burrows with a mixture of neem oil, insecticidal soap, and pepper wax; with virtually no effect.
So far the most effective tactic I've used is to directly spray roach killer insecticide on the adults or otherwise physically kill the adults; then spray the burrows with a residual roach spray pesticide, make a paper capsule/tube of diatomaceous earth; ram rod the capsule of diatomaceous earth into the burrows as if I'm loading flintlock guns, then using a caulking gun and liquid nail to seal the holes.
That last method was a considerable amount of work for me, though it is fairly effective; I would hope that there would be an easier and more effective way of deterring or killing these guys.
It's treated wood that supposed to deter insects; but it's not the old fashion arsenic type of treatment that seemed to be fairly effective at deterring carpenter bees, the new more politically correct treatment does not seem to deter carpenter bees.
I first tried to use pepper wax to deter and/or kill wasps and the carpenter bees; but instead of being deterred or killed they seemed more happy like they enjoyed the extra spice.
I was hoping that I could find something that's more effective then carpenter ant and roach insecticide. They don't seem to be that effective on the carpenter bees, and I don't want to get any overspray on my garden or on other pollinators.
I wish there was some sort of hormone that I could spray on some pieces of wood so that the carpenter bees would go to those sacrificial pieces of wood. If the carpenter bees wouldn't do structural damage to my deck and wheelchair ramp I wouldn't mind having them.
If anyone is thinking about building a deck or a wheelchair ramp you might want to investigate and consider Fiberglas artificial wood for decking material; as you ought to be able to avoid damage from carpenter bees.