Nice little experiment Charlie!  Good idea as far as gluing the mite in
place.
Clearly needs to be replicated with controls and different amounts of OA,
both crystalline, as well as in water, sugar, and glycerol solutions.

I'm not clear why folk continue to bring up OA degradation.  OA dihydrate
is pretty stable, as is OA dissolved in water.  The mode of action is
likely simply due to its acidity (since any other tested acid also kills
varroa).  That means that it is the free H+ (hydronium) ions (which define
acids) that do the trick.  So speaking of OA degradation is likely a red
herring (Dick can chime in if he feels that I'm off base).

Thus, in order for OA to exhibit a biological effect upon varroa, it likely
needs to dissociate in water to free the H+ ions.  This is why Nazzi and
others found that adding humectants such as sugar or glycerol increased
OA's efficacy.

I'm only talking of the chemical mode of action, not the biological reason
for its toxicity to varroa (actual organs or systems affected), which is
another subject.

What this discussion is about is exposure--how the OA physically comes into
contact with the mite, and then how it dissolves into the mite's body
(requiring the presence of water) so that it can exhibit a biological
effect.  The "wet" tarsal pads that Charlie speaks of would be an obvious
suspect route of entry.

I suspect that ambient in-hive humidity would effect the efficacy of
vaporized (and recrystallized) OA against the mite.

And Charlie, I'm completely clear on how agile varroa are.  I question,
however, whether the amount of time that mites spend walking on exposed
(outside of a cell) comb surfaces is more than a very small proportion of
the time that they spend upon bees.  I suspect that their exposure to OA
applied in the hive is predominately from their contact with the
contaminated cuticle of the bees.

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

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html