Bill, I've now got mite count data from 6 test hives.  Two hives have
received 8 vaporizations at roughly 10-day intervals (I used a Varrox for
one hive, a ProVap 110 for the other).  The other four hives have received
4 vaporizations (ProVap 110) at 10-day intervals, with final mite counts
taken 10 days after the last vaporization.

I was surprised that compared to the Control hive, we obtained only roughly
75% efficacy at varroa control.  One of the hives vaped 4 times actually
had its mite level go up.   That said, the repeated vaporizations
eventually got mite levels low in all the rest of the hive, and the
colonies look healthy and their brood looks good.

The unexpectedly-poor efficacy may partially be due to our low
humidity--I'd like to see data from a more humid area.

The first thing that I hear when I present the data is that I should have
vaporized more frequently.  This is based upon the misunderstanding of
logarithmic growth curves--the way that a varroa population increases.  In
such a growth curve, the timing of a percent kill of the total population
doesn't make any difference upon the final outcome.

However, in the case of OA vaporization, which hits the phoretic
(dispersing) mites, one could argue that if you kill them before they can
reenter a cell, then treatments at 5-day intervals could nearly eliminate
the mite population.  Unfortunately, the math doesn't work that way.

I created a mite model (described at
http://scientificbeekeeping.com/the-varroa-problem-part-15/) that
calculates mite population growth on a daily basis, accounting for daily
mite invasion and emergence in the cells.  I ran a simulation this morning
for a colony with 18 frames covered with bees, 4 frames of brood, and a
daily mite immigration of 5 mites--all held constant.  I started with a
total mite population of 5000 in the hive.  Then I entered a 90% kill of
the phoretic mites every single day for 15 days straight.  Those treatments
dropped the total mite population to only 1000.  But by 30 days later, it
was up to 2000.

My point is that we can try to intuit how well a treatment strategy will
work, but for real-life application, the math needs to work, and we need to
collect field data from a number of hives.  I find this subject to be of
interest, and plan to follow up next season with field trials of repeated
vaporizations and dribbles in order to collect hard data.  If anyone in a
humid area would like to collaborate (you'd need a fair number of similar
hives), let me know next spring, and I'll share a protocol.

I'm not at all critical of vaporization per se.  However, I'm concerned
that it's been oversold as a treatment when there is brood present in the
hive.

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

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html