> When you do an alcohol wash you get a 
> pretty decent count of mites per bee, 

But this is not mites per bee for the colony, it is a valid count only for
that sample.
The sample is a different percentage of the colony population for each
colony, as no two colonies have the same population.
But that's just for starters - if you go back the next day and follow the
same process on the same colonies, you will get different numbers of mites
too.

> representative of the whole colonies infestation level.  

This is the assumption that so many people make.
If it were true, we'd all have no problem with varroa.
See Jerry's comments earlier in this thread.

In my view, 300 bees scooped from those shaken from a few frames does NOT
represent the colony as a whole, which is why varroa control continues to
prove so problematic even after so many years.  It is "mites in the sample",
that's all.  The only way to salvage some utility from these measurements is
to track the change in the number of mites found per sample, using the same
method consistently.  It is a sharp upward change in the number of varroa
found per sample that should prompt action.

Perhaps there is a better method out there.  But what we have been doing for
decades clearly isn't working well.

A single measurement just isn't cutting it.  I don't know how to say it any
clearer.  Multiple samples of the same colonies is much more useful, as one
can plot a curve and see where the varroa infestation level really is.  The
slow linear build up is "tolerable", but the start of the ramp-up is the
danger signal.

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