Agricultural publication G7424
— Reviewed October 15, 1996
Darryl P. Sanders
Department of Entomology, University of Missouri-Columbia
The name carpenter bee applies to
several species of bees found in the United States. The only one
of importance in Missouri is a large species, Xylocopa
virginica (L.), which is widely recognized as the carpenter
bee. Like a bumble bee, it is about 1 inch in length and black
with some markings of yellow hair. Unlike that of the bumble
bee, the top surface of the carpenter bee's abdomen lacks yellow
hair markings. It is almost hairless and appears to be entirely
black and rather shiny.
Carpenter bees often fly near
eaves and gables of houses. Residents may become frightened by
this activity because male bees patrol these areas and may fly
near people. They are unable to sting. The females do not
actively defend the nest but will sting if handled.
Habits
Carpenter bees generally are
beneficial insects because they pollinate numerous species of
plants. They may become destructive, however, through their
habit of digging nests in wooden buildings.
People may become alarmed when
holes, about 1/2 inch in diameter, begin to appear in exposed
wood. In addition, unsightly defecation stains are usually
present near these holes.
The entrance hole is a nearly
perfect circle. It usually goes straight into the wood a short
distance, then makes a 90-degree turn and runs with the wood
grain. Several galleries may lead from a single entrance.
The female builds individual
brood cells in the gallery, stocking each with pollen and nectar
before laying an egg and sealing the cell. The new bees emerge
in late summer, feed and then re-enter the galleries for the
winter. In spring they reuse existing galleries or build new
ones. Infestations may persist for several years.
While carpenter bees attack
many species of dried, seasoned wood, they seem to prefer
softwoods such as pine, fir, redwood and cedar. They may damage
porch and shed ceilings, railings, overhead trim, wooden porch
furniture, dead tree limbs, fence posts, wooden shingles, wooden
siding, window sills and wooden doors. They prefer unpainted or
well-weathered wood to painted or hardwood timbers. The wood
preferred is at least 2 inches thick.
Control
Carpenter bees should be treated
after dark when bees are calm, preferably on cool nights. Use a
pressurized can of spray that shoots a stream of liquid for
quick knock-down of bees. This spray is good only for
immobilizing the bees so you can place a residual (longer
lasting) insecticide inside the galleries. Use only one of the
following residual insecticides:
- bendiocarb (Ficam) 1%
dust
- carbaryl (Sevin) 5%
dust or 1% spray
- chlorpyrifos (Dursban)
1% dust or 0.5% spray
- cyfluthrin (Tempo)
0.1% spray
- cypermethrin (Cynoff,
Demon) 0.2% spray
- permethrin (Flee) 0.5%
spray
Dust is most easily placed in the
gallery opening using a hand duster. A flexible lotion bottle
with nozzle makes an acceptable duster. A pin stream of spray
should be used to apply the liquid. Cotton soaked in one of the
liquid insecticides and then placed into the gallery is an
effective application method. Wear rubber gloves while handling
such material.
After treatment, fill the outer
holes with caulking compound, plastic wood or a tight-fitting
wooden dowel glued in place. If paint on the wooden surface is
not undesirable, painting will discourage further attack by
other carpenter bees.
If the bees pose no particular
threat, you might consider delaying preventive measures, since
treating existing nests is easiest and most effective early in
the year. Treat nests before the bees become active. This way
you can be sure that there are no stragglers outside the
treatment area that might start a new nest at a nearby untreated
location.
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