Anobiid beetles

Structure-infesting anobiids (powder post beetles) occur primarily in older homes that have crawl spaces or damp basements. These beetles also infest outbuildings, such as barns or garages. Wooden support timbers, floor joists, and sub-flooring are commonly infested. The insects will attack new hardwoods (maple, walnut, oak) and softwoods (Douglas-fir, cedar, hemlock) or those that have been in service for many years. Larvae also feed on plywood.

New replacement wood attached (or scabbed) over old infested wood is more likely to be attacked and shows damage very quickly.

Here is an excellent pdf from WSU