Powderpost Beetles

Genuine infestations are fairly easy to spot. Real powderpost beetles are usually first discovered when the adult eats a hole in the surface of the wood from within. The (flight) hole will be pin-size (1-3 mm), and when fresh is surrounded by a tiny ring of white powder (frass). The flight holes are perpendicular to the surface and tunnel walls and show a bright raw wood color. Positive identity of the infestation is necessary and is best left to a qualified entomologist, by submitting an insect specimen (taken when the adult beetle exits the hole), or by removing a board suspected of infestation, for laboratory examination.

False alarms: All Oak flooring grades allow the presence of pinworm holes in the face of flooring strips. These holes are in the wood before the lumber is dried and made into flooring. When flooring containing the pinworm holes is sanded and finished, sanding dust and/or filler sift into the holes. As the finish is applied a film is formed over the holes. With traffic, normal expansion/shrinkage, vacuuming, and cleaning the film breaks and the pinworm holes are revealed. They are often about the size of powderpost beetle emergence holes and are sometimes mistaken for real infestations -- often with the help of an unscrupulous pest control agent.

The home owner, seeing these holes suddenly appear, often assumes some sort of live insect is in the wood, and takes measures to treat the floor, generally by calling in a local pest control firm.

Unfortunately, many pest control personnel are not well qualified in identifying insects of this sort, since active infestations seldom occur and the exterminators have little or no first hand experience. As a result an "erroneous" identification of a powderpost beetle infestation is made even if neither the tell-tale ring of white powder nor active adults have been seen. For protection, a pest control operator may recommend the most stringent and expensive treatment, usually complete fumigation. The operator also points out instances of infestation showing extensive damage not only to flooring but other wood articles in the home. Thus the expensive treatment is initiated and the flooring is blamed for the problem. The home owner is now determined to recover the cost of the treatment.

For all these reasons it is in the best interest of all connected with suspected beetle-infested floors to respond immediately to reports of a powderpost beetle complaint. The first order of business is to determine whether the report is genuine or a false alarm. If the tell-tale rings of powder and/or adults are not in evidence and have not been noticed by the home owner the report is almost certainly in error. But if the home owner is unconvinced it is best to have the assessment verified by an entomologist. State university entomology departments are a potential source of help in this regard. Or the NOFMA office can submit samples of suspect wood or captured insects to an entomologist in Memphis for examination for a modest fee.

Infestation:
With proper kiln drying practices, which are required for the manufacture of domestic Oak flooring, it is impossible for any stage of the insect, (egg, larvae, adult) living inside the lumber to survive the kiln heat. The kiln schedule requires temperatures much higher and longer than the insects, eggs, or larvae can withstand. Most mills also kiln dry all dunnage lumber used in pallets and packaging to insure that no lumber leaving the flooring mill can be a source of powderpost beetles. Proper kiln drying, however, does not prevent infestation later.

A genuine powderpost beetle infestation can originate near the house where it occurs, or in storage areas where flooring is kept prior to job site delivery. Small decorative grape vine wreaths have many times been identified as a primary source of the beetles. Other possible sources are imported woods made into moldings, bamboo and other wooden household items. Many of these imported woods and bamboo do not require the strict kiln drying schedules used for Oak flooring. Thus it is possible for any stage of the insects to survive the lower temperatures used to dry these wood species. This makes imported wood a prime suspect as a source for beetles infesting any part of a home, particularly with the increased usage of these imported products.

The cycle begins as the adult lays it eggs in the open sapwood pores of a suitable hardwood, generally; Oak, Ash, Hickory/Pecan etc. Diffuse porous hardwood woods such as Maple, Beech, and Basswood and all softwoods are not suitable sites for egg laying and are not attacked. Stored unfinished flooring and installed unfinished flooring are tempting targets for egg laying. The longer flooring is exposed in these uncontrolled conditions the greater the opportunity for infestation, so long as the area is accessible to a tiny ( 1/8" long) flying insect.

Clues to the infestation's source can sometimes be found in the pattern formed by emergence holes in the floor surface. If, for example, emergence holes occur in roughly a circular pattern spanning several boards the infestation almost certainly occurred after the floor was installed. On the other hand, if the pattern is isolated to individual boards with little overlap, and those are randomly spread about the room, the infestation probably occurred before the flooring was installed, either before or after delivery to the home.

TREATMENT: After an active infestation is determined, control measures may then be performed. Minor problems, where a few scattered boards have been infested, may simply call for spraying the piece with the proper insecticide killing the active beetles and plugging the flight holes as they appear. CAUTION: The insecticide may soften the finish.

In this case a wait and see approach is often recommended since re-infestation is unlikely.

A more extensive problem may require removal of the finish from the infested area and treating with a penetrating insecticide. In more severe cases removal of infested strips and treating the exposed surrounding wood with an insecticide may also be an alternative.

The following reasons make re-infestation unlikely so only a minimum treatment, if any, is necessary in most cases. Aging wood is less likely to be a viable food source for Lyctid beetles, since the starch content in wood declines with age. A limited number of beetles emerge at one time so that there is difficulty with finding a mate and mating. The finish on the wood clogs the open pores and eliminates suitable egg laying sites. Only hardwood sapwood is considered a viable food source. The low moisture content of the wood within a home slows and prolongs larvae activity so the larvae die before maturing.

Treatment by general fumigation, or the removal of flooring, or the removal of the finish and using a penetrating insecticide is required only in the most extreme cases where large numbers of powderpost beetles emerge from all areas of the flooring at one time.

Use of insecticides -- consult a qualified applicator for product recommendations and use, follow label directions, and check for interference with finishing materials.

For more information on this subject consult the NOFMA headquarters or write-
Wood Science & Technology
Mississippi State University
P.O. Box 9820
Mississippi State, MS 39762-9820.