|Carpenter Bee, Xylocopa sp. (R. Bessin, 2000)|
These beneficial pollinators can be intimidating. They are relatively large in size and can cause considerable structural damage over time.
Carpenter bees spend the winter as adults in their gallery homes. Now, they are starting new tunnels or expanding old ones in order to raise a brood of about six larvae during the summer. Accumulations of sawdust may be the first sign that their work has begun.
|Carpenter Bee Tunnel with Larval Cells (USDA Forestry Service, Wood Products Insect Lab Archives)|
Carpenter bees prefer weathered softwood but will chew into stained, treated, or painted wood. Eaves, window trim, facia boards, siding, wooden shakes, decks, and outdoor furniture are satisfactory choices, too. Even pressure-treated, stained, or painted wood is not completely safe from attack.
Carpenter bees are solitary insects, each living in individual tunnels. However, large numbers can build where there is an abundance of suitable nesting material.
Carpenter bee control is not easy, so prevention is the best long-term strategy. Use of hardwoods when practical or covering softwoods with flashing or screen will prevent inijury to areas that are chronically attacked.
Closing barn and shed doors while the bees are establishing new galleries should help to reduce infestations. General maintenance helps because carpenter bees exploit rough areas on wood surfaces to begin a nest. Filling cracks and crevices, and painting or varnishing exposed wood will make it less attractive.
There are some insecticide options but accessibility and dimensions of infested surfaces can make treatment impractical or limit its success. The use of dust formulations of insecticides, applied directly into tunnel openings, has been the favored option. In this approach, bees are exposed to the dust as they enter and leave. Ultimately, they should receive a lethal dose.
Example dusts include boric acid dust, or produces such as Bonide Termite & Carpenter Ant Dust (deltamethrin). Diatomaceous earth and combinations of dusts with desiccants are also possibilities.
Insecticide sprays can be applied into tunnels but pick-up of the dried residue may not be as rapid as with dusts. Insecticide applications to wood may provide some preventive effect but bees are not ingesting the wood, only gouging it away so they can work quickly through the treated surface.
Example sprays include Bayer Home Pest Control Indoor & Outdoor Insect Killer (cyfluthrin), Bonide Total Pest Control Outdoor Formula (permethrin), Bonide Termite & Carpenter Ant Killer Ready to Use (deltamethrin), and Spectracide Bug Stop (1-cyhalothrin).
After treatment, tunnel entries should be filled and sealed so they are not attractive to bees next season.