Ted Fischer mentions that Varroa mites like all biological organisms make up
a population of widely varying individuals. While not disagreeing with this
statement it is worth pointing out that the typical varroa mite is the
product of a brother/ sister mating.  This must dramatically reduce their
genetic variability compared to honeybees where the opposite is the case.
From this it follows that once resistant traits appear among honeybees, as
they surely will in the fullness of time, the difference in mating habits
will have a multiplier effect enabling bees to out-evolve varroa mites.
Chris Slade
Thinking it's not like me to be an optimist: pessimists have all the pleasant
surprises.