Termite and Wood Boring Insects - Termites in panel doors?

Six months ago we moved into a 4-year old townhouse and recently noticed small piles of sawdust under the two sliding panel doors for the closet in my son's room. I took the doors off and saw that the dust comes out of the crack on the bottom where two panels meet (same place on both doors), especially if I shake the doors. There are no other holes in the doors.

The room is not unusually humid and there is no source of moisture anywhere close to the doors--is it possible that there is some wood eater inside the door? If so, how do we determine what kind and how to treat?

It could be that the doors are rubbing on the track and creating the sawdust, especially since you report that the occurrence is in the same place on both doors and that there are no signs of insects or entry or exit holes.

Many thanks, but the doors don't sit in a track, they use sliding wheels at the top. Plus when I shake door, the sawdust seems to be falling from inside. Any other suggestions?

Have you taken down doors and investigated the top of them for insect holes or other possible causes? The frass (sawdust), if there is an insect problem, could be from any one of a variety of woodboring insects. Have you seen signs of ants? Carpenter ants often nest in hollow doors.

http://citybugs.tamu.edu/FastSheets/Ent-1001.html