Dr Marion Ellis and Nick Aliano tested dusting bees in screened cages, which
would be somewhat analogous to packages.  They found that having a solid,
rather than screened, bottom greatly boosted efficacy at removing mites.

The data from our preliminary experiment indicate that 29.7 ±
5.4% of the varroa on adult bees are removed when bees are
dusted with powdered sugar in a box with a screened bottom
and top. We increased percentage mite fall to 76.7 ± 3.6% in our
secondary study by adding solid bottoms to our bee boxes. We
did not succeed in removing 90% of the mites from adult bees
isolated from their nest material as reported by Macedo et al.
(2002). One reason we did not achieve 90% mite fall may be
attributed to not using screened bottom boards to monitor mite
fall after returning bees to their colonies following treatment.
For this reason, the 76.7% mite removal may be an underesti-
mate because mites continue to fall for several hours after dust-
ing adult bees with powdered sugar (personal observation).
However, the 76.7% mite removal represents a level of control
that is comparable to other treatments used to reduce mite pop-
ulations.

We believe that the bee boxes used in the second study were
more effective at knocking off mites from adult bees because
they had a solid bottom, thus ensuring even distribution of pow-
dered sugar on adult bees. Additionally, our solid bottom bee
boxes retained heat, which may have contributed to mite drop.
Three of our treatment colonies in the Pawnee Lake apiary had
100% mite fall, but these colonies also regurgitated honey due
to temperature stress. Subsequent treatment colonies were
checked periodically during their 20–30-minute period in the
bee box to prevent heat stress. In contrast, the boxes used in
our preliminary study had screened bottoms, which allowed
much of the powdered sugar to pass through without sticking
to the bees. We noticed that bees dusted in boxes with screened
bottoms were not as evenly covered with powdered sugar as
those in our solid-bottom bee boxes. The screened bottom also
allowed more ventilation, and such boxes could be left inverted
for over an hour without reaching temperatures high enough to
cause regurgitation. Our results suggest that higher tempera-
tures may increase mite fall when bees are isolated from their
nest material and dusted with powdered sugar.
Journal of Apicultural Research 44(2): 54–57 (2005)

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