> Allen, I don't feel that the argument is circular-- washes are a
 > direct measurement of the mite infestation rate: natural drop
 > is merely a proxy

If you had said "a direct measurement of the mite infestation rate
of a _subset_ of the _adult_ population", I would agree, but washes are 
every bit as much a proxy as drops when it comes to measuring the
actual infestation of the _colony_.

Moreover, in spite of efforts to use either or both these proxies to 
predict what we really want to know -- the likelihood of economic damage 
or colony -- no one has been able to establish a benchmark that can 
predict the tipping point with any precision, outside of the 
experimental situation where it was derived.   The only safe threshold 
is zero, but that is no help.

IMO, Jean-Pierre Chapleau did a nice job for his location, his bees, and 
his varroa using drops. See
http://www.apinovar.com/articles/Varroa%20control%20with%20APINOVAR%20(...).pdf/articlesVarroa%20control%20with%20APINOVAR%20(...).pdf
or use http://tinyurl.com/8rkahzl if that URL breaks.

Pierre Giovenazzo presents an analysis that shows, for his situation, 
that drops had the best correlation in fall.  I posted that on my site 
some time back.
See http://www.honeybeeworld.com/diary/2011/diary021011.htm

 > ...that may or may not reflect the infestation rate, and may be 
influenced by a long list of factors.

... A criticism that can as easily be made of alcohol washes.  Alcohol 
washes are only comparable with other alcohol washes made under the same 
circumstances.

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