Carpenter bees are buzzing

March usually brings the first sightings of carpenter bees in north Florida. While they do resemble the well-known bumblebee, they differ in appearance and behavior.

Carpenter bees are large and robust. The upper surface of their abdomen is bare and shiny black. Bumblebees have a hairy abdomen with at least some yellow markings.

Bumblebees usually nest in the ground whereas carpenter bees tunnel into wood to lay their eggs. Carpenter bees are so named because they excavate galleries in wood to create nest sites. They do not actually consume the wood; rather, they feed on pollen and nectar, making them important pollinators of flowers and trees.

Bare, unpainted or weathered softwoods are preferred especially redwood, cedar, cypress and pine. Painted or pressure-treated wood is much less susceptible to attack. Common nesting sites include eaves, window trim, siding, wooden shakes, decks and outdoor furniture.

Carpenter bees spend the winter as adults within their old nest tunnels. After emerging in the spring, the adults mate and the female begins excavating a gallery with her mandibles (mouthparts) at the rate of one inch in six days. The gallery has a clean-cut, round entrance hole that may be up to one-half inch in diameter.

Damage from a pair of bees is slight, but if the gallery is used over several years, damage can be more severe. Once the gallery is completed, the female begins to provision a brood cell with bee bread, a mixture of pollen and regurgitated nectar. After laying an egg on top of the mass the female closes the cell with chewed wood pulp. Each female may have six to eight sealed brood cells in a linear row in one gallery as she backs outward.

Larvae develop on the pollen/nectar food provided, with the life cycle completed in 30 to 40 days. After the new adults chew through the cell partitions and emerge, they collect and store pollen in the existing galleries, which they use for hibernation during the winter. The previous year's adults die. They are not social insects and there is one generation per year.

Males do not drill tunnels, but they are territorial. Male carpenter bees can be quite aggressive, often hovering in front of people who are around the nests. The males are quite harmless however, since they lack stingers. Female carpenter bees can inflict a painful sting but seldom do unless they are handled or harassed. The males can be distinguished from females by a whitish spot on the front of the face.

The best way to deter the bees is to paint all exposed wood surfaces, especially those which have a history of being attacked. Wood stains and preservatives are less reliable than painting, but will provide some degree of repellency versus bare wood. Preventive sprays applied to wood surfaces are effective only for a short period, meaning that you would have to repeat the application about every two to three weeks.

Once nesting activity has begun, damage may be reduced by treating the entrance holes with an insecticidal spray or dust. Products containing carbaryl (Sevin), cyfluthrin or a number of other pyrethroids (bifenthrin, cyfluthrin, deltamethrin, permethrin, etc.) also are labeled for use against carpenter bees.

Send your gardening questions or comments to: Brunswick County Master Gardener Column, P.O. Box 109, Bolivia, NC 28422, or call 253-2610. Answers may be printed in this column.

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