Once you get the beetles killed off this would be a good application for Bix staining putty. You can mix stain with the powder and once you get the desired consistency, fill the holes with it. If you do a search for "Bix stain putty" you'll find a lot of information.
Here's a review of a few putties also.
http://eclecticproducts.com/_media/AWW_Jun1997.pdf
Most of the firewood I have outside is infested with powder post beetles. When I was renting, my landlord had some firewood stored in the garage and it was infested with death watch beetles. It's amazing how loud the clicks are that they make.
John