>> So the question remains: why don't all hives keep spare queens trapped in
this way?

For the simple reason that hives do not all behave the same way under the
same circumstances, and especially do not all behave in a predictable
fashion when it comes to reproduction of the colony. This unpredictability
is one of my favorite things about bee colonies, though, and makes them
almost as interesting as people. A royal pain to make a living from, though. 

Peter B

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