It could just be cosmetic surface moisture damage. Poke around a bit with a sharp object and see if the wood has softened to any real depth. Termites would be numerous, in the hundreds or more, and easy to spot. Is that a dead ant in your picture? Use a wire brush to remove loose particles.

I'll try that (it's been raining all day here so I'll wait until it dries out a bit, hopefully tomorrow) ... there's lots of funky looking stuff under that fabric liner and I would love NOT to have to move the whole trug to another location (it's close to a garage with wood clapboard now). There are also several creamy white clusters like these, which may be completely unrelated to the wood slat damage; they look like eggs to me and may be perfectly harmless -- even beneficial??