Puffing an insecticidal dust into nest openings that coats the sides of the tunnel is an effective method of removing carpenter bees from an area. Plugging the holes immediately prevents the bees from flying inside and spreading the dust to the rest of the hive, so it is not recommended.
To prevent carpenter bee infestations, homeowners should spray treatments in the spring, mid-summer and early fall. The timing targets bees that are just maturing, bees that may have escaped the initial dusting and bees that may be preparing to winter. After the last dusting, plugging the holes with wood putty or wooden dowels and then painting and varnishing the wood can prevent further infestation.
Caution should be used when treating carpenter bee holes, urges North Carolina State University. The preferred time for dusting is night time, and protective clothing, including a respiratory mask, will minimize stings and exposure to chemicals. In addition, standing upwind of the dust is recommended, and all clothing should be laundered separately as soon as the process is complete.
Sprays are generally not considered an effective treatment method. Even when repeated often, the sprays provide limited protection for wood surfaces, and the bees are rarely exposed to fatal amounts of insecticide. Carpenter bees can also target any wood in a house, making sprays an impractical and potentially dangerous method of population control.