Question
Jim,
   If you're a "disease" guy, not an "insect" guy, could you pls pass our question to the right person, if you know one?
   We observe relatively large, bee-like insects eating the bark from the young river birch trees in our Northern Virginia yard.  Colored like yellow jackets - dark "upper body", yellow "lower body", length one to one and a quarter inches, they appear to have stripped the bark at various heights above approx six feet on both trees.  Work in groups.  These are not the bronze borers or leaf mites I saw on an arborist's web page.
  Trees show no signs of distress yet, but it doesn't look good.  Do we need a pro to spray, or is there another route?  Any advice much appreciated.  Thanks.

Answer
From your discription it would be hard to guess what insect is your problem. I would suggest you call the Va. State Forestry Agency and ask one of their Foresters to come to your place and diagnose the problem. This is a free service and IF the local forester can not determine the cause ask him to send the sample to Va. Forestry Pest Management Chief Tim Tigner, He should be able to help.  Good luck!