Parasitic nematodes might work as a control agent. (Steinernamatid Spp) Possibly parasitic wasps. They both parasitize grubs. Some parasitic nematodes will move around and look for prey. They Deposit their eggs in the grub, they hatch, the grub is eaten from the inside. They don't hurt animals or humans. Pine beetles are listed as a target population. (This variety of nematodes also take care of cut worms, white grubs and mole crickets too.) Unlike pesticides, which cant get inside the trunk, and has to be periodically reapplied, these biological controls reproduce as long as the food supply exists.
For a picture and information:
http://www.biologicco.com/orgpage.htm
and
http://www.vintagerosery.com/bugs.htm