Q: We have a vacation home at Lake Anna. Last year, we got our dining room remodeled with wood cabinetry, a coffered ceiling and live-edge shelves (which include the bark or layer of wood immediately underneath). Our cabinetry guy had never done live-edge shelves and got the wood kiln-dried from a source he had never used previously. Fast forward to this summer and we started noticing small piles of sawdust on the floor below the lower shelf and on top of one of the shelves. Apparently we have some sort of powderpost beetle in at least two of the shelves. Our cabinet guy tented the room and fumigated it. But the next morning, another small sawdust pile appeared. I worry about another infestation. What should we do?
A: You probably don’t need to do much other than clean up the sawdust piles for a while. As long as your vacation house does not get really moist inside, there is little chance that the insects will spread into other wood, and they should die on their own, said Michael Potter, an entomology professor at the University of Kentucky who is often consulted about complex pest-control issues.
There are three main types of powderpost beetles: lyctids, bostrichids and anobiids. All leave wood peppered with pinholes. You’ll probably never see the adult beetles because they shun light. And anyway, it’s the larvae that produce the fine wood powder as they tunnel through the wood. A pest-control expert can feel the sawdust and make a fairly accurate identification, because lyctid powder feels like talc, bostrichid powder feels like cornmeal and anobiid powder feels gritty. But whether you even need to consult a pest-control expert is debatable, given these insects’ life cycles.
Anobiids are the only type that attacks both softwoods, which are commonly used in the framing of houses, and hardwoods, generally found in cabinetry, furniture and flooring. But they need really damp wood, with a moisture content higher than 14 percent, for larvae to develop. In houses with heating and air conditioning, the moisture level is usually around 10 percent. That’s why anobiids create structural damage primarily in damp crawl spaces or leaky attics.
Lyctid beetles lay eggs that develop into larvae only in bare hardwood that has been harvested and cut into lumber fairly recently. The larvae need wood with a high starch content, which declines as the wood ages. Even if larvae already in the wood emerge as adult beetles ready to mate, they will not drill holes to lay eggs in wood that has a finish of any kind, even just wax or stain, Potter said.
Bostrichids, too, are unlikely to come back because they need wood that has a relatively high moisture and starch content.
With live-edge wood, you might also see pinholes made by other kinds of insects, such as shothole borers or bark beetles, Potter said. But these insects attack trees when they are living. They won’t produce new generations within your home.
If you’re willing to wait for the infestation to die on its own, you should see the piles of sawdust peter out over the next year, perhaps sooner. The powder is usually most abundant from late winter to early summer, Potter said. But as the starch content of the wood declines, it takes longer for the larvae, particularly lyctids, to mature. So, you could still see the results of the initial infestation for up to five years. “Seventy-five percent might emerge the first year,” Potter said.
Waiting may seem too scary, particularly if you don’t heat or cool your vacation home while you are away and aren’t sure about the moisture content inside. “If you start seeing more and more holes and get more and more anxious about winding up with Swiss cheese, talk to the cabinetmaker about replacing the wood,” Potter suggested. Or try one of the other proven ways of killing powderpost larvae. But trying to treat the wood in place by somehow fumigating one room won’t work. “What the cabinet guy did is completely ridiculous,” Potter said.
For fumigation to be effective, your whole house would need to be tented and infused with sulfuryl fluoride, or you would need to take the shelves to a company that has a fumigation vault. Find these companies by searching online for “tent fumigation” or “vault fumigation.”
Or, instead of having the wood fumigated, you might be able to kill the larvae using heat. For bedbug infestations, many pest-control companies have invested in chambers where they can kill bugs by heating mattresses and other infested items. To kill powderpost larvae, the wood would need to be heated to 120 to 140 degrees for about 24 hours, Potter said. It’s also possible to kill the larvae by freezing them. Try finding a commercial freezer or meat company with a locker that’s big enough. The wood would need to be kept at zero degrees or lower for four to seven days.
There is nothing you can brush or spray on that will work, Potter said. Borates do work, but only on bare wood that is still moist. The moisture is needed to help transport the treatment deep into the wood.
But, as noted earlier, all of these complicated solutions probably aren’t necessary. “Wipe up the powder and keep an eye on it,” Potter said. “It likely will run its course.”