Todd said:

> ...have not found any simple rule of thumb for what I would call an
> "action" threshold.

> When doing a 24 hour mite drop count (with varroa screen/sticky
> board), is there any consensus on what count should prompt treatment?

Well, there is one, and it has even been tweaked a few times, but I feel
that it will do you more harm than good.

Keith Delaplane and Mike Hood did a series of studies that prompted
them to offer a current treatment threshold" of 59 to 187 mites.
(See http://www.ent.uga.edu/bees/Research/archives.htm for abstracts,
#8, #10, and #22 are the ones to read.)

I attended a talk he gave yesterday on this very subject at the VA/MD
joint state meeting.  He talked about the study summarized in #22
on the web page.

But think for yourself a moment.  What meaning does a number have without
a point of reference?  How can you ever use numbers without comparing them?

Colonies vary in bee population, amount of brood, and levels of infestation.
Colonies also vary in ALL things over time.  Let's take some fictional "cases",
and see how far down the rabbit whole an "absolute number" can take us.

Let's assume that you have a mite count of "50" for each of four colonies.
Using the "single number" approach, you walk away happy.  But you won't
be happy for long.

Here's some cheap-and-dirty estimates of "the rest of the story":

                        Colony 1        Colony 2        Colony 3        Colony 4

Mite Count              50              50              50              50
Brood Frames    4               5               8               11
Estimated Bees  25,000  35,000  60,000  70,000

Ummmm... which colony needs treatment?

Clearly, some standard method of estimating bee populations
and comparing to mite drops is mission-critical to the effort.

One can go further, and say that "You don't know" unless you know what
the mite count was last week, (or last month, if you are really lazy)
and you can compare both mite counts to a bee population estimate done
at the same time as the mite counts.

One can go even further, and say that the numbers above have completely
different meanings in early spring ("April") versus early summer ("June")
versus late summer ("August").

Note that the numbers I listed above for the Colonies are completely
"made up", but my point is that the same "threshold" number or range
cannot possibly apply to all colonies at all times.

I'd suggest that natural mite drop counts tracked over time are much
more useful, as one can more clearly see a "jump" in the counts, and
compare to an indicator of bee population (frames covered with bees,
frames of brood, whatever).  If varroa spikes "up", and bees have not
"spiked up", then one is approaching the "danger zone".

In regard to the Delaplane/Hood numbers, their studies were done over a less
than
2-year period, so they did not follow colonies over even the period that many
hives have survived without any treatment at all.

So, a true "threshold" is not a single number, but a difference between "this
time"
and "last time", both compared to bee population, and referenced to some sort of
seasonal constant.  Something like:


        (Mite Drop Now)        (Mite Drop Last Time)     (Delta Mites)
      ------------------  -  ---------------------  =  -------------
      (Brood Frames Now)     (Brood Frames Then)        (Delta Bees)


Now, if the Bee/Mite ratio "last time" is much smaller than the Bee/Mite
ratio, "this time", you have a real understanding of the situation, and
can compare the ratios of different colonies to get a feel for which are
the "badly infested" ones.  One can also get a feel for "typical" mite
to bee ratios at different times of the year if one keeps a notebook.

Let me stress that Delaplane and Hood are doing important work, and that
they are uncovering much that is useful (for example, they have shown that
even "hygienic queens" and screen bottom boards will not control varroa
when used together).

But my lack of enthusiasm for a "single number" approach to IPM is so strong
that I feel that the "single number" approach is "Idiotic Pest Management"
rather than "Intelligent Pest Management".

As far as true "Integrated Pest Management" goes, I think that the best that
can be said is that we can now alternate between a "hard" chemical (Apistan or
Check-Mite) and a softer approach, like Api-Life VAR, and PERHAPS skip treating
some colonies at all some years.

But no one can say (yet) exactly what sort of mite/bee ratio a colony can
"live with", and more important, no one can say much about long-term survival
of colonies where a threshold ratio is not exceeded, and a decision to not
treat in fall is made.

Wyatt Mangum is doing very interesting things.  He is looking at both "natural"
24-hour mite drop AND 24-hour Apistan strip drops over more colonies, and over
a multi-year period.  He is also building a good dataset on "drifting mites",
brought in by drifting bees.

Wyatt's numbers may allow the creation of a good model for relative bee and mite
populations, ongoing re-infestation via drifting, and seasonal growth.  He may
even be able to give us a "baseline" infestation rate due to drift, which would
be very valuable.

So, just as it was last year, and the year before, and the year before that...

        "the price of honey is eternal vigilance".


                        jim

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