Male and female carpenter bees are becoming active after spending winter in last year’s tunnels. These large yellow and black bees have shiny, bare abdomens (Figure 1) in contrast to the ‘hairy’ ones of bumble bees (Figure 2).
Female carpenter bees can sting if handled roughly, but they do not aggressively defend their nests or otherwise pose a threat. They focus on developing nesting tunnels and collecting pollen. Males, recognizable by the yellow spot on their face, stay near nesting sites and often investigate intruders who enter ‘their’ space. While an intimidating sight, they do not have stingers.
Carpenter bees are important wild pollinators. However, their nesting habits can cause unacceptable damage to structures. They nest in plant material; the soft or weathered wood of structures provides a desirable resource for them. Females use their strong mandibles to chew 1/2-inch diameter entry holes into soft, dry wood and then turn 90o to chew along the grain. A season’s work result in 6 to 10 inches of tunnel and can contain 6 or 7 cells in which individual larvae develop. Each cell is stocked with a ball of pollen, which is food for the grub-like larva. Over the years, galleries may become several feet long. While carpenter bees are solitary, many can accumulate over time in wood that meets their requirement or is near good pollen sources.
Carpenter bee control is a challenge. Their tunnels may be in inaccessible places or so abundant that it is impractical to treat all of them. The best tactic is to initiate control early when the overwintering insects are just beginning to prepare their galleries for the season’s brood.
Dust formulations of insecticides applied into tunnel openings has been the traditional option. In this approach, bees are exposed to the dust as they enter and leave the gallery. They may ingest the product during grooming or the insecticide may enter through thin areas of the exoskeleton. Example dusts include boric acid dust, or products such as Bonide Termite & Carpenter Ant Dust (deltamethrin). Diatomaceous earth and combinations of dusts with desiccants are also possibilities.
Insecticide sprays can be applied in tunnels, but bees may not pick-up of the dried residue as rapidly as dusts. 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), Spectracide Bug Stop (l-cyhalothrin).
About a week after treatment, plug tunnel entrances with a piece of dowel rod so these sites are not used next season by bees looking for nesting sites.
By Lee Townsend, Extension Entomologist