Your Guide to POWDERPOST BEETLES

Your Guide To POWDERPOST BEETLES About the Author Understanding Dr. Michael F. Potter is a professor and entomologist at the Powderpost University of Kentucky, specializing in pests infesting buildings, people and property. Beetles Before joining UK in 1991, How to diagnose problems and develop a prudent plan for Potter worked in the pest management and customers. BY MICHAEL F. POTTER agrichemicals industry. He’s worked with wood- owderpost beetles are second only to termites in their infesting insects for many Pthreat to seasoned wood. Yet the pests still cause a lot of years, providing insights confusion. The chaos often starts with holes and powder ap- and advice to the public. pearing in flooring, cabinets or furniture. Other times, the damage is discovered during a routine wood-destroying insect inspection. Before you All photos, except as noted, arrive, the customer may have ©M.F. Potter. already received incorrect information about whether the PCT Media Group culprits are indeed powderpost beetles. Mistakes also are This educational aid is made determining if infesta- courtesy of PCT magazine, tions are active, and if so, how a monthly trade publica- tion distributed to pest they should be managed. This management professionals study guide will help you throughout North America. make better decisions when PCT magazine and its you encounter these pests. website, www.pctonline. com, is published by GIE Media, Valley View, Ohio. The Culprits. “Powderpost To order additional copies, beetle” is a term used to visit store.pctonline.com. describe several species of 1 3 small ( ⁄8- ⁄4 inch long) insects that reduce wood to a flour- like powder. The larvae make Figure 1. Powderpost beetles narrow, meandering tunnels tunnel through wood, producing in wood as they feed (Figure 1). fine powder and small exit holes. Powderpost Beetles Fact Sheet Your Guide To POWDERPOST BEETLES Bed bugs before and after engorgement. Figure 2. Lyctid powderpost beetles. The powder is the consistency of flour. Newly emerged adults mate and lay eggs the holes. Lyctids attack only wood products on or below the surface of raw, unfinished manufactured from hardwoods such as oak, wood. The eggs hatch into larvae that tunnel ash, walnut, hickory, poplar or cherry. Con- within the wood, emerging as adults, months sequently, problems typically arise in floors, to years later. Infestations are usually discov- cabinetry, molding, paneling and furniture. ered after noticing powder, accompanied by Tropical hardwoods (mahogany, obeche, small, round ‘shot holes’ in the wood surface. bamboo, etc.) are especially prone to infesta- These are exit holes where adult beetles have tion due to poor storage and drying practices chewed out of the wood after completing before importation. their development. Because the adults are Lyctid powderpost beetles do not infest active mainly at night, customers are more pine and other softwoods, so structural wood likely to see holes and powder than the members are generally immune from attack. beetles themselves. Occasionally a beetle may This is important to communicate to custom- be spotted emerging from an exit hole or on a ers, who often worry that infestations will windowsill, since some are attracted to light. spread into walls, studs, etc. Lyctids also The three most destructive groups of avoid construction plywood used for sub- powderpost beetles are the lyctids, anobiids, floors and sheathing (although plywood with and bostrichids. Each group contains several a hardwood veneer may sustain damage to species capable of damaging wood materi- the outer layer). als. Many similar-looking beetles that do After emergence and mating, lyctids locate not infest wood also appear in buildings. susceptible wood to lay their eggs. Ten to Correct identification is important to avoid 50 eggs per female are inserted into the tiny embarrassing, costly, and potentially litigious pores and vessels of unfinished hardwoods. mistakes (see sidebar, ‘Mistaken Identities’). Stained, varnished, or painted surfaces are immune from attack; beetles already within 1 1 Lyctid powderpost beetles are small ( ⁄16- ⁄4 infested wood, however, can emerge through inch), narrow and elongated, reddish-brown subsequently finished surfaces. Before de- to black beetles (Figure 2). Their emergence positing eggs, female lyctid beetles ‘test’ holes are round and about the size of a pin- the suitability of wood for the larvae, which head. The powdery dust feels like flour or fine require starches and sugars for development. talc and often accumulates in small piles near If the starch content of the wood is insuf- Powderpost Beetles Fact Sheet Your Guide To POWDERPOST BEETLES ficient (less than about 3%), the females will not use it for egg laying. Lower starch levels also make it harder for the larvae to com- plete their development. Lyctids are less particular about moisture than other types of powderpost beetles. Larvae can persist in wood with a moisture content as low as about 8%, which is common in temperature- controlled, indoor environments. However, at such low moisture levels, beetles develop more slowly, as occurs in older wood with declining starch content. In newly seasoned wood with abundant starch and other nutrients, egg to adult development takes less than a year. Con- versely, as wood ages, starch content de- clines and development slows to the point where some beetles may not emerge for two or more years, if at all. Consequently, lyctid infestations eventually cease and die off even without intervention — an important factor Figure 3. Bostrichid powderpost beetles often have when weighing options (see section, ‘Remedy- rasp-like bumps behind the head. Some species ing Infestations’). Small numbers of lyctid also have a pair of projecting spines at the end of the body. beetles already in the wood may continue to emerge for up to five years, in rare cases, even a bit longer. Customers should be unusual habit of boring directly into wood apprised of this possibility, and that the in order to lay eggs. These holes are devoid prolonged emergence is due to diminished of powder. Conversely, holes formed by suitability of the wood rather than re- beetles upon completing their development infestation by other beetles. are packed with powder. The powder/frass is more meal-like than lyctid powder and tends Bostrichid powderpost beetles vary in size to remain tightly packed in the holes and feed- depending on the species. Those most associ- ing galleries of the larvae. ated with wood products are reddish-brown Bostrichid powderpost beetles are more 1 1 to black ranging in length from ⁄8- ⁄4 inch. serious pests of hardwood than softwood, Compared to lyctids, bostrichids are less and there is little risk to structural framing narrow-bodied and flattened, and the head within homes. Similar to lyctids, bostrichids is oriented downward, appearing ‘hooded’ usually attack newly processed wood with (Figure 3). Many species also have tiny, high starch and moisture content. Tropical rasp-like bumps behind the head, sometimes hardwoods, including bamboo, are espe- accompanied by a pair of projecting spines cially prone to attack, which often occurs at the end of the body. Bostrichids create before importation. Like lyctids, bostrichids 1 1 circular ⁄8- ⁄4 inch holes in wood like other seldom re-infest wood after the first genera- powderpost beetles. Female beetles have the tion emerges. Nonetheless, extensive damage Powderpost Beetles Fact Sheet Your Guide To POWDERPOST BEETLES to infest moist wood; a 13-30% moisture content is required for development of the larvae. Besides needing wood moisture for larval development, high humidity is essential for egg hatch. At 65-95% relative humidity, more than 80% of eggs successfully hatch; below 60% humidity, hatch is reduced to zero. Consequently, infestations are most severe in damp crawl spaces, basements, garages, and unheated outbuildings. Buildings with central heating and cooling seldom have sufficient dampness to support beetle development in living areas or attics. Anobiids occur throughout much of the country. Structural infestations are more common in the southeastern and coastal states where humidity and temperature are high and crawl space construction is abundant. Unlike lyctids and bostrichids, anobiid powderpost beetles can digest the cellulose within wood, and are less dependent on starch and other nutrients that decline over Figure 4. Anobiid powderpost beetles can re-infest time. This enables them to attack and in- damp wood repeatedly. Massive damage to this fest wood regardless of age. In Europe, for beam occurred in a bourbon warehouse in Kentucky. example, some anobiid species continue to infest wood in buildings that are centuries old. can occur the first year due to a high initial Larval development occurs slowly, exceeding population and rapid development. 2-3 years if conditions are suboptimal. As a result, infestations are seldom obvious in Anobiid powderpost beetles are convex, red- buildings less than 10 years old. Although dish to dark brown beetles capable of attack- damage occurs slowly, the ability of emerging both hardwoods and softwoods (Figure 4). ing beetles to re-infest wood year after year They are sometimes confused with drugstore can lead to serious problems requiring treat- and cigarette beetles that also occur in homes ment and repair. but infest stored foods. The emergence holes Emergence of adults usually occurs dur- 1 1 are ⁄16- ⁄8 inch. Rubbed between the fingers, ing spring and summer. In nature, the beetles the powder feels gritty (although when the dwell in dead tree limbs or bark-free trunk source is oak or another hardwood this is scars. The adults are strong fliers and some are not the case). Unlike the groups discussed attracted to lights. Infestations within build- previously, anobiid powderpost beetles can ings may originate from infested lumber, fire- seriously damage beams, joists, and other wood, or from beetles entering from outdoors. structural components of buildings. Moisture is the most crucial factor affecting the destruc- Is the Infestation Active? Powderpost beetle tive potential of this beetle.

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