>
> > all colonies where either in same yard or very nearby ones, which is
> wrong also.


Dee has a valid point here.  With most trials, you want all colonies in the
same yard to avoid another variable due to location.  But when in trials
testing varroa, the drift of mites from colony to colony can be a problem.

Such drift would presumably follow the diffusion model, in which the net
drift of mites would tend to to be from areas of high concentration to
those of low concentration.  In other words, from colonies with high mite
levels to those with lower levels.

This process might mask the effect of subtle mite resistance.  But if the
treatment (e.g., small cell) had a robust effect, the result should still
be evident.

Dr. Rinderer's group deal with this effect in their trials of Russians and
VSH vs. commercial stocks.

If one is isolated from major mite immigration from outside (non resistant)
stocks, varroa management is much easier.  I see this regularly in the case
of hobby beekeepers who purchase nucs from me--the nucs often survive for
years with out any mite treatments.
-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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