Vince,
I agree with your comment about the queens' genes and selection for the
appropriate destination.  However, I do not agree with your comment about
treating bees with antibiotic.  The point is that you are not treating the
bees but the bacteria.  By doing so you are subjecting them to a strong
selective pressure.  While bees will have about one generation a year in which
to evolve, the generations of bacteria are measured in minutes or hours and
evolution of resistant strains of bacteria to antibiotic will be
correspondingly faster than the resistance of bees to the bacteria especially
if they are relieved of the selective pressure by indiscriminate use of
antibiotics.  I am writing as a reasonably well read beekeeper, not as a
scientist.  Perhaps Garth or another scientist would like to comment on my
logic.
Chris Slade