>Within the limits of our study and at the application rates used, we did
not find that dusting colonies with powdered sugar afforded significant
varroa control.

Thanks, Pete,

I've been corresponding with the authors. The key words are "within the
limites of our study" and "significant."

Someone could look at their Figure 4 and come to the conclusion that sugar
dusting was very effective, since after a year's treatment, the dusted
colonies had less than a third the mites that they started with, whereas the
control colonies returned to the original mite levels.  However, the
differences were not *statistically* different (although when looking at the
standard errors I couldn't understand why).  Unfortunately, the authors
declined to share the original data with me to analyze independently.

Note also that this trial was held in Florida, and the mite population
dynamics were very different during this trial than those for most temperate
areas.  Note that the mite populations in both the test and control groups
dropped during the summer, which is the opposite of what happens in most
temperate areas.  This factor alone made any test of efficacy difficult.

This was an excellent and meticulous trial, but it may not really tell us
anything new beyond what I have already posted to my website.  Top dusting
with powdered sugar at the frequency they used (every two weeks), during
periods of brood rearing will decrease mite population increase to some
extent, but may not drop the level below the initial level (although their
Fig 4 shows a substantial intial drop).

Sugar dusting is a useful tool in mite management, and may well see improved
application methods that will result in greater efficacy, but it is not a
panacea.

Randy Oliver

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