>The compounds which are most effective in controlling varroa -- kill them.

Not necessarily.  A behavioral disruptor such as amitraz does not need to
kill any mites to be effective, if applied before the mite level gets too
high.

Any chemical that messes with mite olfaction (such as formic vapors,
possibly oxalic acid, and perhaps some essential oils) could reduce varroa
reproductive success, leading to control over time.

>either solid or powdered thymol would be very difficult for the bees to
physically remove, assuming the carry it out in their mandibles

I need to watch closely to confirm, but suspect that bees would have no
problem with small crystals.  They eagerly tug at fibrous material treated
with thymol.  And quickly remove the polyacrylate particles interspersed
with thymol (the thymol does not dissolve to any extent in Apiguard gel).

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

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