Two colonies, ESBA1 at the association's place and one of my own, have Buckfasty bees in them now which I don't think were raised by the resident queen. Both are the westmost colonies at their sites, and in one at least the bees at the east side of the original box seemed uniform and dark but the intruders (if that is what they were) were at the other side. Frames at rt angles to the entrance and boxes facing south.

Am I witnessing the contamination of the area with imports? Will drones from them now cross with my queens? Is this subsidised from the public purse? Or is this coincidence and the queens are now finding different packets of sperm from the corner of their spermathecas?

Here are dark bees from ESBA1, close-up and more distant, and a frame with some very different looking bees from the same colony (the split with the original queen). Also Jon's plot (posted in the 'Your gallery' thread) from the sample of bees taken from the E side of the box and which were all dark.