> However, as soon as there is a virgin queen, who can easily get through a
> queen excluder, the swarm will leave with her!

The virgin will not get through the excluder any easier that the old queen.
It's the thorax of the queen that's bigger than workers, not the abdomen.
Actually, the method of using an excluder for swarm prevention is used by
many beekeepers. It's a simple way of avoiding swarms to leave the hive.
But it has it's draw backs. Firstly, all drones will get trapped above the
excluder and finally die there and reduce the ventilation of the hive. Workers
will chew them down and dispose of them, but there will be less drones in
the air for mating and it might be a problem when working with breeding.

When the first swarm try to leave, the old queen will soon be killed by the
first
emerging virgin. She will then try to leave in a swarm, and the bees will fly
in and out of the hive for some time without being able to get the queen with
them. After some time, there will only be one virgin left in the hive. At that
stage
the excluder HAS to be removed in order to let the virgin fly to mate.

This system works well, if timed properly. It's draw backs are the amount of
dead drones on the excluder blocking ventilation, and the difficulty to keep any

record of the genetics.

--
Regards

P-O Gustafsson, Sweden
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