Sawyer Beetles vs. Powderpost Beetles in Timber Frames

Wood-Boring Beetles in Eastern White Pine: Know the Difference

Finding live grubs in ½-inch holes in freshly cut timber frames raises alarm. The critical question: will emerging adults reinfest the structure?

Sawyer Beetles (Monochamus spp.)

• Roundheaded borers; larvae feed under bark and in sapwood of dead/dying conifers.
• Make loud chewing noises (“sawyers”).
• Adults emerge from firewood/logs but do not reinfest seasoned structural wood.
• Nuisance only; no structural threat.

Powderpost Beetles (Anobiidae, Lyctidae, Bostrichidae)

• Flatheaded or roundheaded; larvae bore into dry, seasoned wood.
• Prefer high-moisture softwoods (pine, fir) in poorly ventilated areas.
• Can reinfest if wood moisture remains high (>14–16%).
• Exit holes: round (1/16–1/8″) with fine flour-like frass.

Your Situation

Live grub extracted from a ½″ hole in green timber suggests a sawyer or other roundheaded borer that infested the log before cutting. Since the frames are now drying, reinfestation is unlikely if moisture drops below 12–14% quickly.

Immediate Actions

1. Kiln-dry or air-dry frames to <12% MC ASAP.
2. Small pieces: microwave 1 minute to kill larvae.
3. Heat-treat entire timbers to 136°F core for 30 minutes (commercial kiln).
4. Apply borate spray (Tim-bor, Bora-Care) to surfaces for residual protection.

Long-Term

Keep frames dry, well-ventilated, off ground. Monitor for fresh frass. Sawyer beetles won’t return; powderpost beetles only if moisture creeps up.