>
> >It would also make sense if what really happened was a local evolution of
> less virulent mites.


Mike, I've tried to make that hypothesis work mathematically.  The problem
is that if there are ANY colonies with virulent mites around, then they
will always outcompete avirulent mites.  This is apparently what happened
in Brazil when the Korea strain replaced the less successful ("virulent")
Japan strain.

>I was referring to the notion that small isolated populations of honey
bees can develop mite resistance and that this resistance can be passed
along by propagating the queens therefrom.

Dr. Denis Anderson and I discussed this at length some years ago.  His
study of varroa in Asia led him to believe that there is a continual
evolutionary adjustment going on between local populations of varroa and
their local race of Apis cerana.

What I'm seeing in practical application is what Tom Rinderer keeps
pointing out--that a local race of bees can develop resistance mechanisms
that work if that race is the predominant race in the area.  But if you
place hives of a more susceptible race of bees within flight range,
transmission of mites from them to the resistant hives overloads the
resistance mechanisms.

This brings us back to Charlie's question of a while ago about mite
immigration causing regression to the mean.  The recent study by Helen
Thompson confirms the substantial amount of drift between hives.  My own
data indicate that in a yard of hives, a few will likely exhibit mite
levels far above the mean--often 25-50x as high as those colonies with the
least amount of infestation.  Those few "mite bombs" may well tip the
balance in favor of the mite.

As Jose suggests, isolation (or more properly, genetic limitation of the
local breeding population) are likely critical for success.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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