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 Frass that is yellow and caked is "old" and may indicate an infestation that is no longer active.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