Moni

But termites are not hard to see. So, I guess it could be some kind of borer. There are so many different kinds that I cannot begin to guess which ones. I think I might try first giving the tree a good long soak, just to get anything in the soil to come up for air. Then I might try to find all of the holes and stick a thin wire into them and wiggle the wire around a bit. That would help kill whatever is tunneling those holes. But I have to add that insects usually destroy what has already been weakened. You can often get borers in a healthy tree but the free running sap, etc. usually helps to protect that tree. And that is for "normal" trees growing in the ground. Bonsai tends to put some trees under stress, anyway. Just thinking out loud here. At least with bonsai, the trees are small enough where the wire method is not prohibitive. Give it a try.
Moni