It seems that this is an extraordinary year for Carpenter Bees or homeowners are extraordinarily sick of them. In either case, we are posting information that comes from the Ohio State Agricultural Extension Service report on Carpenter Bees.
Use WD 40, wasp/hornet killer spray, spray a liquid in the entry hole and plug with steel wool. PLEASE DON’T.
REAM out the chamber/tunnel with a wire. This breaks up the waxy pockets that house the larvae and serve as “condos” for the adults during the dormant periods.
DUST the entry hole with a powdered type insect killer such as Drione or Sevin Dust. The dusts are superior for killing carpenter bees because the dust gets on their bodies and they carry it into the back of the chamber to kill the entire nest. It is almost impossible to get a liquid all the way to the back of the tunnel.
LEAVE the hole OPEN for a few days at minimum.
CAULK the hole.
ADD NBS30 to your paint or stain and proceed.