there  were about ten percent double
> queens, but I saw no link to aggressive  behaviour.



Hi Tim,
 
Ron Brown used to lecture on his 2 queen system.  Copies of his  pamphlet are 
still available although he doesn't lecture much nowadays as he is  95 now.  
One of the benefits he cites for the 2 queen system is improved  temperament, 
which he puts down to the extra queen pheromone in the hive.
 
Chris

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