>  >55 mites per 24 hours in early September...

And for your particular location, with your
particular type of bee, and your particular
mix of management practices, I'm sure that you 
can rely on continuing to take heavy losses if you 
ignore that sort of mite drop rate in September.

But what does someone 200 miles South of you do?
And when do they do it?

And what about someone 200 miles North?
What do they do, and when do they do it?

What would the >>>general case<<< be, I wonder?
What general-purpose tool might be used in a
consistent manner by all beekeepers, regardless
of the location of their hives, and the seasonal
weather progression where their hives are?

And what of migratory beekeepers?  What might
they do?

Well, they could take advantage of the experience
of EVERY OTHER segment of agriculture, and their
IPM programs, which are based on doing more than
one measurement of one variable.

> I'm roughly familiar with several studies that 
> "proved" the value of thresholds. 

That's the great thing about thresholds!  There
are so many different ones to choose from!  :)

Seriously, do a simple Google search for "varroa"
and "threshold", and just look at all the different
numbers being batted about as if they were authoritative.

And that's the wonderful thing about "studies"
they can go through all the rigorus steps of
proving a conclusion, yet ignore that the
data is inherently local in nature.

Of course one can, after the fact, see with 20/20
hindsight and say "hives with varroa counts higher
than x died", and conclude that hives with lower 
varroa counts that survived did not need treatment.
But even this hindsight is not 20/20, as mere
survival is not enough in beekeeping.  Worse yet,
the data is specific to location, weather, and
a host of other factors that tend to vary from
operation to operations.

So, the "knowledge" yields little or nothing in the 
way of a metric that applies anywhere else, or to 
anyone else's bees.  We end up with a different 
threshold for every USDA zone, or perhaps even zip code.

So, I'll insist again - thresholds are bunk.
An unscientific approach with no more value than 
a guess, at odds with the basic precepts of IPM as
practiced in every other aspect of agriculture.

We have no one to blame but ourselves.  Beekeepers
whined and complained that they "just wanted a number".
We can't really blame the extension community for
coming up with thresholds in response to those 
repeated demands.

Don't teach me basic concepts, don't help me to
understand the relationship between pest and host,
don't teach me to MANAGE the problem at all.
Just give me a number.

No wonder varroa still takes hives and frustrates
beekeepers more than 20 years after it first showed 
up in the western hemisphere! 

******************************************************
* Full guidelines for BEE-L posting are at:          *
* http://www.honeybeeworld.com/bee-l/guidelines.htm  *
******************************************************