Thanks for the arithmetic correction Charlie--so much for doing math in my
head : )
However, even at 1000 potential mite drift (I wasn't talking about
collapse, but rather pre collapse drifting), that's still a fair amount of
mites.

So much for theory.  I also observe the same as you--that one hive in a
group can have sky high mite counts (in one of our untreated mite test
yards two weeks ago, one hive had 120 mites in an alcohol wash of 300 bees
(the queen was a test queen from another source).  But a number of nearby
hives had zeroes to 5's.  So there was clearly not a robust flow of mites
from high density to low density hives.

As you know, I'm also frustrated in trying to figure out the math of the
drift issue.  It clearly occurs in the case of collapsing hives being
robbed out.  But absent robbing, if drift were a major distributor of
mites, we'd see mite counts equalize throughout the apiary.

But I just don't see that happening in the field absent collapses.  When we
do mite washes, it is not the least bit unusual to find adjacent hives with
widely different mite infestation rates.

BTW, I'm in complete agreement with your observation that the increase in
late summer mite infestation rate, as measured by sampling of adult bees,
is driven by the reduction in the hive bee population due to reduced
broodrearing,  The population of bees suddenly decreases faster than the
population of mites.

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

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