If you are having a problem with carpenter bees, it is best to get rid of them as soon as possible. carpenter bees do not really eat wood, but they chew out holes and makes nests inside, where eggs hatch and create more carpenter bees, increasing the destruction. The good news is that they are susceptible to most flying insect pesticides, and the holes can be filled fairly easily.
Step 1: Prevention Saves Time
If your wood is covered with a thick coat of exterior wood paint, you will probably not have much trouble with carpenter bees. The bees actually chew into the wood to make holes, and they don't like the taste of paints. The most likely reason is that the bees recognize their nesting material by taste, and painted wood does not taste like a nest should be flavored.
Step 2: Stained Woods
If your exposed wood has an exterior wood stain, but is not sealed with polyurethane or some other wood sealant, bees may still be a problem. Most stains only penetrate a few microns into the surface of wood, and bees will quickly chew through to the real wood, and begin nesting. If you want to use stained lumber, be sure to seal it appropriately to protect the wood from pests and weathering.
Step 3: Pesticides
When possible, avoid the use of chemical pesticides. In this case, they are the easiest solution, however, as you can simply point the nozzle at the hole, and release a short blast to kill all of the carpenters bees and their larvae. You do no have to drench the area, but simply get a little of the bug poison inside the hole. As you plug the hole, fumes will continue to kill any bees or eggs that remain inside the wall, including queens.
Step 4: Stuff It
Use newspaper and stuff the hole to within 1/2 inch of being full. Use a small stick or the head of a nail to compress the paper inside the hole. You can also use caulk, but since this is a completely non-visible repair, there is little to be gained from using more material than necessary.
Step 5: Plug the Hole
Using a putty knife, fill the hole with wood putty. Apply the putty firmly, forcing it as deep into the hole as possible, and packing it tightly. Allow the wood putty to dry for 4 to 6 hours before painting.
Step 6: Prevention Saves Time
As stated at the very beginning, your best recourse is to prevent any problems from happening. Seal all wood, including the edges and joints. Make it so that carpenter bees do not recognize your wood as a place to build nests, and they will find another location. Bees are not smart, and a millimeter or so of paint or polyurethane is all it take to confuse them and send them off in search of greener forests.