I think there's one in Baton Rouge, La. and for sure there is one in Beltsville, Md.
Yes, there is a USDA bee lab in Baton Rouge...Not sure, but I want to say there are three nationally, There use to be 4, but the one in Texas closed a little over a year ago...I know at that time there were three remaining, not sure if maybe they've gone down to two since then or not.
Anyway, the one in Baton Rouge is only about 20 minutes from me, I was scheduled to go to their annual field day this year but the government shutdown caused that to be canceled...But over the last year I've since members of their staff (currently at eight) speak at the Baton Rouge Bee club numerous times, as well as a number of their staff speak at the State convention this weekend.
My point is, I've never heard anyone on their staff, or anyone at either of my local clubs, or anyone at the state convention refer to the USDA lab as the place to go for any type of analysis of ones personal bees.
While it seems "logical"....I don't think the USDA Bee labs would be where you would go to get that done.