I think if it were me I would follow Karl's advice on the borate
solution anyway, just to make sure there wasn't *something* in there.
About 5 years ago I turned a large bowl with long sweeping sides on it
for a friend from an old ash stump I had. That stump was about 3-4
years old, and had been sitting on a cinder block outside the house
aging (read: in the firewood pile).
I turned it, sanded it, admired all the inclusions to that gave it so
much character and gave it away. In two weeks there were little bits
of sawdust around the bowl, and after that it got worse. I mounted
the bowl and cut the walls thinner and there were some kind of borers
that has been there all along. I didn't know they could last that
long, but they were quite healthy.
As for the floor, I have used different approaches depending on what
the end result was to be used for. For nail holes and other small
occlusions, i have use a small forstner bit in an electric hand drill,
and drilled out the offending area and plugged it with a dowel.
Worked great. I got that idea from when I was a helper and it was my
job to go behind the carpenters that counter sunk the screws in the
work, and I had to back behind them and put a plug in, cut it off with
a chisel and sand it smooth.
I used store bought dowels then. But with this you could actually
match the grain and just about make your plug disappear:
This is my favorite for fixing larger problems and again, you can
match the grain pretty easily depending on the wood. One of my amigos
has this set and just loves it. He wound up buying a couple more of
the patterns, since he had way too much fun playing with this: