Hi Grant and Peter,

I wanted to wait until I processed all data before I published
results. Take anything below as a rough estimate of my preliminary
perusal of the data.  Unfortunately, I got distracted by Nosema
ceranae before I could crank all the numbers.

I found that dusting at 4-day intervals did not result in any *major*
drop in natural mite fall after 12 days.

Dusting singles weekly kept mite levels from increasing midsummer, but
was not effective at making levels drop.

Yes, dusting makes lots of mites drop quickly--I've seen 200 mites
drop in less than a minute from a 5-frame colony!

So sugar dusting does indeed drop a lot of mites (about half the
phoretics, it appears, but I need to reconcile some data before I
stand behind that number).  Unfortunately, the remaining mites in the
brood make up for the drop to some extent.

So sugar dusting is useful to slow the exponential growth of mite
populations, but was not effective in my trials at *dropping* mite
levels.

Yes, you are entirely correct about the individual situation.  I have
not tested in a high humidity area.  Local hobbyists claim great
success with dusting, but some also claim great success doing nothing!

One thing is clear to me in California--varroa is more of a problem in
large apiaries than in a hobbyist situation with a few colonies.
Don't know why, it seems that drift and robbing issues should be
similar.

The mite drop for the first hour post dusting is an extremely accurate
assessment of mite level in the colony--it appears to be far more
accurate than natural mite drop, and likely more accurate than the
alcohol was of 300 bees.

Even the 10-minute drop had a 42% correlation with the alcohol wash.
This method is an extremely fast way to compare mite levels in all
colonies in a yard.  We can test a yard of 36 in about 20
minutes--providing that all colonies have screened bottoms.

We use dry corrugated signboard to catch the mites--no sticky.  Then
the boards can be slapped against the side of a hive to remove the
sugar, and reused time and again.

We glance at the boards and do a simple triage--zero to a few mites,
5-10 mites, more than 10.  This sorts our colonies into potential
breeders, normal treatment, or immediate treatment and mark to
requeen, depending upon the time of season.

Mite levels vary so much year to year that I dare not extrapolate
management recommendations.  Last year, most of my colonies did well
with an oxalic dribble just after Christmas, dustings every second
month or month as I checked mite levels, and a single Apiguard thymol
gel application in August.  Some required a second application.

Some colonies required no thymol at all.  However, there was
considerable loss of colonies that I thought has low enough mite
levels to make it without.

I should add that I practice only minimal drone trapping in my
management, since we nuc all colonies after almonds, and need large
drone numbers in early spring for mating queens.  I have been trying
to perform a trial of drone trapping plus sugar dusting for the
season, but have not yet been able to.

Randy Oliver
Ningaloo Reef, Australia

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