Q&A: Grass-carrying wasps and powderpost beetles


November 30, 2017

Email your questions about insect identification and pest management technologies to pmpeditor@northcoastmedia.net. Your questions most likely will be printed and answered in one of Pest Management Professional’s upcoming columns.

Q: I am finding small “nests” of grass in window frames in a home. I’ve seen this before, but have never found anyone who knows what causes this. Do you have an idea?
— Mike G., Virginia

A: I suspect you are looking at nests made by grass-carrying wasps (Isodontia spp.). These tiny wasps collect grass clippings to make the nest. They then find a suitable insect, sting it to paralyze it and stuff it into the nest. Eggs are laid, and the larvae feed on the paralyzed insect.

The wasps are relatively harmless. If control is needed, any residual applied to the window frames after removing the nests solves the problem.

Q: A homeowner has a powderpost beetle (Lyctinae) infestation in relatively new kitchen cabinets. Frass is everywhere. The cabinets are three years old. All surfaces have a finish. The bottom of all the drawers and shelves are infested. I’m looking for ideas other than ripping out the cabinets and replacing them. What are my options, and might the manufacturer be liable?
—Jan T., Louisiana

A: Because all of the surfaces are finished, the infestation most likely was in the wood before the cabinets were constructed. However, most cabinet manufacturers will fight and take the position that the infestation took place after the cabinets were installed. The infestation did not manifest itself until three years later, so a judgment could go either way. Therefore, I would not suggest the homeowner take the cabinet manufacturer to court for a long, drawn-out legal battle — although a letter from an attorney might be worthwhile.

Option No. 1: If the drawers and shelves are the only pieces infested, remove the drawers and shelves and fumigate them. Option No. 2: Heat the cabinets in place. The interior of the wood members must reach a temperature of 130°F to kill all stages. Option No. 3: Fumigate the house, which is relatively expensive and probably would exceed the cost of the cabinets.

Option No. 4: Ignore the infestation and let it run its course. Most emergence should take place this year. Next year, there may be a few isolated emergence holes, but that should end the infestation. Treating with a borate or other pesticide will not solve the problem because the wood is finished. Discuss these options with the homeowner.

Q: An old house has a powderpost beetle infestation that appears to be active. Can heat be used to control this problem? If so, how much heat is needed?
—Barry B., Connecticut

A: As mentioned in the previous response, heat can be used — but you must get the center of the wood up to 130°F to achieve total kill. Even 2x4s require several hours to reach this critical temperature. Thick beams — 6x10s, for example — might require days of heat to reach the critical temperature. Heat is a viable option for small wooden artifacts, which can be heated to the critical temperature quickly.

A borate treatment is less expensive, and provides residual protection as well if the infested wood is accessible. Another option is fumigation, which is expensive and provides no future protection.

If you find that a beetle in the Anobiidae family causes the infestation instead (deathwatch beetles, furniture beetles, etc.), drying out the structure so the wood has a moisture content below 12 percent also will eliminate the infestation.

You can reach Dr. Doug Mampe, an industry consultant, at dentomol@aol.com.


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