> Hybrid vigor usually refers to "a lack of inbreeding weakness".

I don't think it means that on this side of the pond.  Here we 
differentiate between inbreeding, outbreeding and cross breeding.  We 
would only look for inbreeding when trying to fix lines in order to get 
recessive genes to be expressed so that they can be culled out or to 
subsequently outbreed for one generation to take advantage of the 
resulting vigour.  I see outbreeding as mating between unrelated bees 
but from the same race.  That is a sustainable option and the one most 
of us try to adopt. It provides a "lack of inbreeding weakness" without 
producing hybrids. Then there is cross breeding which involves the 
crossing of different races.  In my experience you then the get the 
hybrid vigour that leads to aggressive behaviour in the next 
generation.  The first such cross gets the honey but the second gets the 
aggression.  The only person I have known who did this regularly was 
very careful to requeen every year.  Unfortunately he used to sell some 
of his old queens and the unsuspecting purchasers found themselves in 
all sorts of trouble the following year.

Steve Rose, North Wales

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