"Have you considered that the hives that swarmed had a low population of winter bees going into winter? That would not directly explain the nosema but winter may have been more stressful on "old" bees which made them more vulnerable to a Nosema outbreak?"
 
Yes, although it wasn't apparent from the activity at the entrance.  Sept swarms are almost a death warrent for the hive that swarms.  I have had some recover, but most don't.  These had laying queens going into winter, just not enough time to recover from swarming.  Then add on top of that the nosema, and it's a one two punch.  I have yet to figure out why they would swarm in the first place, as there was plenty of room.  Any ideas?
 
Jim  
 
http://www.northernqueens.com/
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