It's hard to confirm the identification of this insect from this photo (not sure on the coloration and the size of this insect).  If these bees are noticeably smaller than yellow jackets that you're used to seeing then it is likely a totally different species. (Yellow jackets & bees don't continue growing once they are in their adult form.)

A couple of possible options to help with an identification: You can drop off samples of dead insects at the OSU Extension Benton County office.  Our Master Gardener volunteers will be able to do some research and get you back an answer.

Another option is to compare what you're seeing to some photos. This link is from a Christmas Tree publication, but the photos are great to compare different species of yellow jackets.  Scroll down and then click on the photos to enlarge them.  Does this look similar to what you are seeing?

Hope this helps at least sort out if what you are seeing is or isn't a yellow jacket!
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