I had Russians as well. They are a funny bees to me. Hard to re queen. Want to make their own. Been discussed before. I had a couple of Russian hives that were "mixed" with local that re queened themselves. I finally let them have their way. I think the stock was good and they contributed to the overall gene pool. The two I have left are quit the mix of dark and light bees. It actually seems to fluctuate. More light bees in the summer and more dark bees now. Just speculation. I guess my point is the Russians(any strain ?) seem to get assimilated and perhaps exhibit a collective collage of the genes in the area unless pure strain is put back in. Just thinking out loud.
Interesting study that seems to fit into this discussion.