>I don't think anyone argues drift at all,  but there are many of us still
pretty skeptical of the math involved for this to be a major factor.

Let's say that 1 colony out of 10 collapses in an area.  A late-summer
collapsing colony can contain 30,000 mites.  If only half those mites drift
to the other 9 hives, that would be, on average, roughly 1700 mites
invading each of the other hives.  That number could easily tip colony
health of the other hives.

A November collapse involves a smaller number of mites per hive--perhaps
13,000.  Using the same parameters as above, that could cause the drift of
an average of 722 mites to each of the surrounding hives, a post-treatment
addition that could easily put many of them over the tip point for winter
survival.

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

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