Powderpost Beetles
We use the term "powderpost beetles" for several
groups of small woodboring beetles. In North Carolina, our primary
concern is with anobiid ("an-oh-be-id") powderpost
beetles, which attack the "softwoods", such as spruce,
pine and fir, that are used to make floor joists, wall studs
and other structural lumber. Lyctid ("lick-tid") powderpost
beetles attack only hardwoods, such asoak, hickory, and maple.
They tend to be a problem with antique furniture,
cabinets, wooden floors and some moldings in houses. The term
"powderpost" refers to the type of damage caused
by the beetles. Infested wood may look fine on the outside.
Only months or years later do we discover the damage. We rarely
find the actual beetles. Typically, the only indication of
a powderpost beetle infestation are small round holes, about
 1/32
- 1/16 inch in diameter, scattered over the wood surface.
In some cases, only one or a few boards are infested. In other
instances, several joists may show sign of powderpost beetle
activity. At first sight, people often assume that these holes
are made by insects boring into the wood. The holes are actually
made by adult beetles exiting the wood after they complete
their life cycle. As it emerges from the hole, the beetle
pushes out light-colored flour-like "frass" (yellow
arrows) that will be found streaming from these holes or on
the ground beneath the infested boards. The frass of the lyctid
beetles looks and feels like talcum powder. The frass of anobiids
is powdery, but has a gritty texture. Frass that is yellow
and caked is "old" and may indicate an infestation
that is no longer active. You may find exit holes and frass
almost any time of the year, particularly in heated buildings
or in crawlspaces. However, the peak time to watch for emerging
beetles occurs in May through August.
You cannot simply look at a piece of wood to determine
if the damage is severe enough to require repair or replacement.
Probing the wood may give you some indication of the extent
of the damage. If you are concerned about the condition of
structural wood, such as floor joists, you should contact
a structural engineer.
Powderpost Beetle Control Many
powderpost beetle problems
are related to high moisture (near 20%) in the wood, particularly
in crawlspaces. Moisture readings should be taken from floor
joists by a pest control operator when he/she inspects your
home. You can reduce moisture in the crawlspace by improving
the ventilation and/or installing a 6-8 mil plastic moisture
barrier covering 70-80% of the soil. Spraying the wood with
an insecticide is the most common method of chemical control
for powderpost beetles. Pesticides containing "borate"
are especially effective against powderpost beetle because
they penetrate the wood and kill beetles within wood, as well
as killing adults entering or exiting the wood surface. If
you are concerned that wood behind walls or in other inaccessible
areas is infested, then it may be necessary to fumigate. If
you find activity in late fall or in the winter, you might
want to wait until spring before treating so you can tell
if the problem is limited only to that area or is more extensive.
Prepared by
Michael Waldvogel, Extension Entomology Specialist and
Larry Jahn, Extension Wood Products Specialist
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