Powder post beetles cause damage to wood structures, floors, millwork, and furniture. They can infest and cause damage in well air-dried and kiln-dried lumber. Generally, they do not attack green lumber or logs. Powder post beetles include several species of small insects (1/16”– 1/4” long) that are not often seen, but infestations typically are discovered by the presence of adult beetle emergence holes and nearby flour-like powder or frass. The frass is produced by larvae as they tunnel into the wood to feed and develop. They emerge from the wood as adults, mate, lay eggs on or beneath the surface of unfinished wood, and then die. The eggs hatch and the larvae tunnel into the wood, typically emerging as adults about one to five years later.
The adult emergence holes on the wood surface are small, round “shot holes.” The size of the holes is an indicator of the type of powder post beetle infesting the wood.
The exit holes of lyctid powder post beetles range from 1/32” to 1/16” in diameter, with damage being confined to sapwood. Lyctids attack only hardwood lumber such as ash, cherry, hickory, oak, pecan, and sycamore. Lyctid infestations also can occur in tropical hardwoods and bamboo. They do not eat the cellulose found in wood; instead, they require starch to develop and grow. Newly dried lumber has abundant starch for lyctids, and they can mature in less than a year, making it likely that powder post beetle damage in a new home is caused by the lyctid beetle. As wood ages, starch levels decrease and lyctid development slows to the point that it may take up to five years. Lyctids can attack wood having a moisture content between eight and 30 percent.
The anobiid powder post beetle makes a slightly larger exit hole ranging from 1/16” to 1/8” in diameter. Anobiid damage occurs mostly in the sapwood, although rarely it may occur in heartwood.
Anobiid powder post beetles can attack softwoods such as pine, spruce, and fir, in addition to hardwoods, making them a problem for structures that typically are built with softwoods. Anobiids can eat the cellulose and are not so dependent on starch that declines over time. Hence, they can attack old wood as well as recently manufactured wood. Anobiids need higher wood moisture content than lyctids: the ideal moisture content for anobiids ranges from 13 to 30 percent.
It is probably an understatement to say that having a powder post beetle infestation in flooring, lumber, or other wood products is unpleasant. A powder post beetle infestation can be challenging for the homeowner, installer, supplier, and manufacturer.
There are six suggested approaches to manage a powder post beetle infestation.
1. Prevention. Powder post beetle infestations happen after wood has been sawn and dried and then sits in storage, or during transit and distribution. Lyctid powder post beetles typically enter buildings on manufactured goods such as flooring and molding. They will not attack finished surfaces that have been varnished, waxed, or painted. An important step in preventing a lyctid infestation is to maintain kiln-dried lumber at kiln-dried moisture content during storage. As previously noted, lyctids prefer wood at moisture content greater than eight percent. Remember to practice first-in-first-out (FIFO) with your inventory when warehousing lumber or flooring. Wood that sits for an extended period of time has a greater chance of being found by powder post beetles that will lay eggs on the wood.
Anobiid powder post beetles, unlike the lyctids, can damage structural components of buildings, especially in damp crawl spaces, basements, and garages. Moisture content of 13 percent and lower will discourage anobiid growth. A plastic moisture barrier in the crawlspace covering 70-80 percent of the soil will reduce moisture in the crawlspace and help prevent an anobiid infestation.
2. Replacement. If the infestation is limited to a few pieces of flooring or trim, replacing the infected and adjacent pieces of wood is an effective approach. This works well if lyctids are the culprit since they do not readily re-infest finished wood indoors that has low moisture content and declining starch content found in older wood.
3. Elevated Temperatures. Properly kiln-dried lumber will kill powder post eggs, larvae, and adult beetles. Effective kiln drying, however, does not prevent re-infestation during shipment or storage. Infested furniture and similar wood objects can be placed in a heat chamber that can heat the wood to 135°F for up to 24 hours, depending on the
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4. Moisture Content. Low moisture content discourages the development of powder post beetles, hence moisture control is an important tool. This is especially important in the crawlspace to prevent anobiids, as previously discussed.
5. Borates. If the wood is not finished, a borate spray can be applied which can, to a limited extent, penetrate and kill powder post beetles in the wood. The higher the moisture content, the deeper the borate will penetrate. A finished floor must be sanded before the borate spray is applied. Since re-infestation of finished flooring by the emerging adult lyctids is unlikely, especially if the moisture content is low (10 percent or less), sanding and borate application may not be necessary.
6. Fumigation. In structures where powder post beetles have spread into areas that cannot be reached for surface treatment or removal, fumigation may be an option. For structures, this would involve enclosure with a sealed tarp and the evacuation of people and animals for about three days, during which time the gas concentration is monitored. Unfortunately, fumigants currently available are not as effective as those used in the past, and there is a chance that the fumigation will not be successful. For items that can be moved, some pest control companies have chambers in which fumigation can be done.
In summary, the best management tool is prevention by good inventory management, the control of moisture content in kiln-dried wood, and application of a finish to the wood surface.
Dr. Phil Mitchell is associate professor and wood products extension specialist at North Carolina State University in Raleigh, North Carolina. He has taught industry-oriented workshops covering a variety of topics including: lumber drying; lumber cut-up optimization; lumber grading: wood gluing, wood-moisture relations, lean implementation, and CNC manufacturing. He is author of “Rough Mill Improvement Guide for Managers and Supervisors, and Strategies for the New American Furniture Industry.” For more information about the NC State Wood Product Extension, visit https://sites.cnr.ncsu.edu/wpe.