Thanks for the reply Jerry.  It seems that there may be some
misunderstanding in semantics in this discussion.  When I am referring to a
"treatment threshold," I'm not referring to any single number at any single
time point.  That concept was dismissed by successful beekeepers long ago.

The most consistently successful beekeepers that I speak with keep a close
eye on the average mite infestation rate of their operation throughout the
year, and never allow it to get to worrisome levels. A mite level that
causes concern at any time of the season would indicate that it is over the
threshold of concern, and initiate action (treatment) on the part of the
beekeeper--thus a "treatment threshold."

Others, especially those relying upon off-label amitraz, may practice
simple calendar treatment, often gambling on the date of fall
treatment--the choice being between timely treatment or leaving their honey
supers on as long as possible (many operations later crash if they make the
wrong call).

 Although commercial guys use different methods for monitoring  mite
levels, it appears to me that the most reliable are ether rolls,  "wash"
samples, or "accelerated drops" (using a strong miticide, and then
adjusting for colony strength, which adds room for error)(the accelerated
drop would not technically be a "sample," since it is applied to the entire
colony population).

Although some get hung up on the inherent inaccuracy of any sampling
method, I don't understand why they get so distracted by this.  I have
published plenty of data on the consistency of mite levels of samples taken
from various frames from the same hive or on adjacent dates.  I don't have
a problem with the amount of inherent variation, especially considering
that I never allow mite levels to get to a point that such a small degree
of deviation would make any practical difference.  I see that Brion has
recently posted a small data set that strongly supports this claim.

Other than when robbing or drifting are involved, mite buildup follows an
easily predictable trajectory, based upon varroa's intrinsic rate of
reproduction when brood is present.  If one regularly monitors mite levels
in multiple colonies in the operation, one gains a good feeling as to how
that trajectory is progressing.  In a large beekeeping operation, one of
course cannot track every individual hive, so must deal with averages on a
yard-to-yard or area-to-area basis.

Some of us commercial guys discuss what we are seeing in early spring, and
if it appears that the trajectory is accelerated (perhaps due to a warm
winter, or lack of good control in fall), then we get onto treatment
earlier than normal.  If the trajectory is depressed (lower than expected
mite buildup), then we may be able to skip a treatment (some outstanding
Calif commercial guys may treat more than a half dozen times over the
course of the season; others treat only after almonds, and then again in
late summer).

All goes out the window in late summer and fall when collapse of nearby
hives can result in huge mite immigration.  In our operation, we sample on
a daily basis during that period of time so not to be caught by surprise.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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