Aug 28, 2014 - 09:03 AM
Could be any number of wood infesting insects. Depending on the amount of dust, it could be a wood boring beetle. I would look and see if you can find any evidence of "kick out" holes, or holes that this dust is falling from. Also look for signs of live or dead beetles or ants.
I really can't give you much advice on how to treat until we figure out what the insect is. They are different and the control is different.