[PCT on the Road] Mystery Holes in Wood

As their name indicates, wood-destroying beetles can damage the appearance of wood and cause structural damage. Because this group of insects is made up of different species, there are different approaches for their management. “The more you know about them, the easier they are to manage,” said USDA Forest Service Entomologist John Kyhl, in his 2007 Minnesota Structural Pest Management Conference presentation Mystery Holes in Wood, which focused on identification and management of wood-destroying pests, especially powderpost beetles.

Wood-destroying beetles feed on wood in any condition, from healthy and green wood in the forest to processed lumber. One group of wood-destroying beetles, the powderpost beetles, can be a particular challenge to identify and control because of their hidden harborages, small size, and their ability to readily survive for long periods of time in processed wood. These beetles are common in natural, wooded areas, Kyhl said, living in the dead wood of trees. Unfortunately, they pass freely from this setting, enter structures and feast on wood inside.

LYCTID LARVAE. Of the five main groups of powderpost beetles, the most common group is the “true” powderpost beetles: Lyctids. Adults are about one-quarter inch long, and live only a couple of weeks. These beetles are most damaging in the larval stage, when they feed on wood for several months to several years. Lyctids commonly re-infest wood from which they emerge, laying an entirely new generation of tiny, cylindrical eggs in its pores, emergence holes and cracks. From these pores, the larvae then burrow into the wood through tiny, virtually invisible, entry holes.

Keys to identification of true powderpost beetles are their preference for hardwoods and bamboo, but most importantly, the creation of a talc-like frass, with no grittiness to it. “They’re kind of picky,” Kyhl adds. They almost always infest sapwood and, though they can be found in older wood, they are most likely to seek out younger wood, of five years or less, which retains a higher quality and starch content on which they feed.

TAKE ANOTHER LOOK. Lyctids often are misidentified as stored product pests (grain beetles). For proper identification, this pest should be viewed from above, where the head can be seen and a large club at the tip of the antennae is evident.

As is common in our industry, the most critical aspect of management is proper identification. In this case, Kyhl said, it is not necessary to identify the species, but identification must extend down to the particular group, because different groups are managed differently. This is of particular importance in locating the beetle for elimination. Questions to be asked in identification include:

• What is the consistency of the frass?
• What is the size of the exit hole?
• Is the beetle infesting hard or soft wood?
• What is the condition of the wood — wet or dry, new or old?
• Is there an active population or is it old damage?

The answers to each of these questions provide clues to the specific identification and management of these beetles.

The author is a frequent contributor to PCT magazine.