my father made some ash cabinets a couple years ago and had the same problem. yours could just be one local bug that got into it, or it could be a whole colony like he had. he ripped it all out and started over, if you have more than just a couple that maybe be a good option.....
I believe boric acid was what a customer used on a heart pine floor , with powder post bettles. You will need to know what your dealing with first as far as insect goes.