> I poured powdered sugar
> liberally on each seam of bees.  The drop was 39 mites.

My understanding is that to treat properly with powdered sugar, one must
remove the frames one at a time and dust all the bees on both surfaces, not
just pour sugar along the top of the interspaces. Very small particles of
sugar must contact pretty well everything on each surface for the technique
to work, I should think.  I remember this detail because I was concerned
about open brood when I read about the technique.

Another consideration, particularly in damp environments, is that powdered
sugar will clump.  That clumping may not be obvious to the naked eye, but
when we used to mix OTC with icing sugar, we checked under magnification and
could see were not getting very good mixture due to this clumping.  As a
result, we wound up using a flour siftter to ensure the particles were
separated.

Talc or some other very fine dust might be worth a try, too, but the
dehydrating effect of the sugar particle -- if it actually contacts a
mite -- may be what gets the mite to let go.

allen
http://www.internode.net/honeybee/diary/