Bill Truesdell asks about a concoction of different oils of essence (a more
correct name for essential oils).

> 100 gram bottle of thymol, Add 1/2 ounce of menthol and 1/2 ounce of
> champhor...
> This treatment was developed by Nick Calderone when he worked at
> Beltsville....

Nick's work was initially very promising, his concoction appeared highly
effective and there was quite a stir in the beekeeping community.  There
were others doing similar work (James Armine in West Virginia for one) on
oils of essence.  I believe Jim's work is available online, although I don't
recall the url, but it's in the BEE-L archives.  Calderone was doing his
work right around the time he succeeded Roger Morse at Cornell.  Subsequent
experiments had less promising results.  Conclusions were that the treatment
can be highly effective, sometimes, but not reliably.

This seems to be a common theme in the varroa saga.  A treatment looks
effective, but doesn't stand up to scrutiny.  It's a long list including
oils of essence, mineral oil, screened bottom boards, smoker fuels (many of
which have been touted - cedar shavings, stag horn sumac, grapefruit leaves,
...).
Most of these treatments have been discussed and disseminated on BEE-L, have
been quickly picked up by the beekeeping community and have subsequently not
stood up to field laboratory studies.  The rapid dissemination of "shaky
science" has been an oft heard criticism of BEE-L and internet lists in
general, which is why you have to be cautious of what you read and try.

And this is not to say that none of the treatments discussed here or
mentioned above are useless.  Many are included in the arsenal of IPM.  The
problem with these treatments is that they don't achieve the levels of
control that did Apistan or does for the time being (resistance is already
showing up in where else? Italy!) Coumophos.  That the above mentioned
treatments do not achieve 99% knock down of varroa has had them looked upon
with lesser favor from the commercial ranks, where time of treatment (labor
costs) is a big part of the considerations.  However, ever 99% knock down is
being reexamined as a goal, as it's that remaining 1% that breeds the
resistance to the treatment du jour.  The latest aim is to reach the
"economic threshold", defined as the level of varroa a hive (or yard) can
tolerate without causing economic loss.  I understand the concept, but find
it laughable.  With the dynamics of varroa populations, the economic
threshold this week can grow exponentially to crash level and severe
economic losses in a very short time.

But anything that can knock back (not eliminate) the varroa population is a
good thing.  A round of drone trapping is a set back in an exponential
curve.  A less than 99% knock down achieved by an oils of essence treatment
is a set back in an exponential curve.  Mesh bottoms alone, still show an
exponential curve, although the rate of increase is not as dramatic.
Combinations of the above treatments give continual set backs in the
exponential curves, and can keep varroa populations below the "economic
threshold" if the threshold in your operation does not include the labor
costs to employ the method(s) of control.

Aaron Morris - thinking like a mathematician!