In response to Rob Biddleman's query for Ormond Aebi about varroa, I
don't claim to be an expert, but I'll be glad to pass on what I gleaned
from a pamphlet distributed at our local beekeepers association
(unfortunately, I no longer have the pamphlet and I forget the source,
although I seem to recall that it's the producers of Apistan).  I'm
thrilled to pass on to Ormond what I know, in a small attempt to
return what he has passed on to me through his book, which I thoroughly
enjoyed!
   The life cycle of Varroa is such that varroa eggs and nymphs are
laid/hatch/wait for their host in individual cells in the comb.  When
bee pupae are capped, the adult varroa attach themselves and hence are
already on the emerging bee.  The mites have a preference for drone
cells, but I haven't a clue as to how they distinguish drone cells from
worker cells.
   The only treatment I have used is Apistan (something Ormond would
disdain).  I lost two hives this winter (even though I treated in the
fall) and dead mites were left all over the bottom boards.  I would
assume that once varroa decimate an area they will die off.
Unfortunately, it would take MASSIVE die offs on a large scale to
eradicate mites from an entire area.  Even if one's entire apiary is
wiped out, starting over from scratch gives no guarantee that there
won't be mites in hives in the next county over.  My question would be,
how do mites spread from hive to hive?  If the mites enter bees in the
cell, then how does a mite-less hive pick up the first mite?  The best
guess I can take at this one is drifting, but that's just a SWAG.
   So, I've written what I know and have ended with a question.  I hope
this will help, or at least lead to a more boisterous discussion.