Archive for Sunday, May 23, 2004

Carpenter bees wreak havoc on structures

May 23, 2004


Wood is arguably the most used building material in construction. It's used to build houses, decks, furniture and other structures. If left untreated or unprotected, it will be damaged by wood rot or decay, termites, carpenter ants and carpenter bees. Although the latter are less common and the least damaging, carpenter bees are starting to show up in home landscapes.

Here's what you need to know to take the sting out of these wood-destroying insects:

They buzz, hover and look like bumblebees. However, carpenter bees are very different in appearance and habit. Bumblebees have hairy, yellow-and-black abdomens, whereas carpenter bees have hairless, shiny blue-black abdomens. Bumblebees are generally about a third larger than carpenter bees, which lack pollen baskets on their hind legs.

Carpenter bees are solitary, meaning they do not nest together. The female is capable of delivering a sting, however she will only do so if prodded or provoked. Male carpenter bees, meanwhile, are much more aggressive and will buzz around a person's head trying to defend themselves and their territory. The males do not have a stinger and are harmless.

Female carpenter bees have strong jaws that they use to bore into, primarily, unfinished wood. She will bore a perfectly round 3/8-inch hole straight into the wood. Usually the only sign of carpenter bee activity is the small hole and sawdust below the hole. Although the damage may appear minimal, the tunnels can extend into the wood as far as 6 inches. Damage caused by a single bee is slight. However, the cumulative efforts of many carpenter bees can be structurally damaging.

Carpenter bees overwinter as adults. They emerge in April and May to mate. Fertilized females lay their eggs within newly excavated tunnels or old ones that they have enlarged to reuse. An individual egg is deposited in each of six to eight cells off a main tunnel.

Developing larvae feed on "bee bread' made of pollen and nectar regurgitated by the female bee. Larvae become adults by late August and September but do not emerge until the following spring.

Wood can be somewhat protected by applying one or two coats of paint. For added protection, consider using pressure-treated lumber when constructing outdoor projects. Unfortunately, wood stains do not offer much protection. Aerosol insecticides or insecticidal dusts, such as carbaryl (Sevin) or a synthetic pyrethroid (permethrin or cyfluthrin), can be used to treat carpenter bee entryways. Sprays may only be effective for one to two weeks, so retreatment may be necessary. Excavated tunnels are best treated with an insecticidal dust that contains 5 percent carbaryl puffed into the tunnel opening. After carpenter bees have had an "in-and-out" access time of several days, holes can be filled with wood putty to discourage future use of already excavated tunnels.

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