>
> >I do not understand why OA would damage mites but not bees.  Can anyone
> explain?


This is a good question, and a couple of possible answers come to mind:

1.  That it is simply a matter of surface to body mass ratio--a varroa mite
has far more surface relative to body mass than does a bee.  This
explanation assumes that the OA is absorbed over the entire body surface,
which is apparently dependent upon humidity, as well as any humectants
added to the OA.

2.  That the mite's sticky tarsal pad is more prone towards absorption than
is a bee's arolium (http://www.pnas.org/content/98/11/6215.full.pdf).  And
this may also relate to (1) above, since the arolium: body mass ratio of a
mite would be greater than that of a bee.  A question is whether the bees,
when walking on comb, predominately use their tarsal claws, or whether they
extend their arolia.

3.  That bees, due to their evolutionary exposure to oxalic acid in plant
products, may be better adapted to deal with (metabolize) OA than are
varroa, which are adapted to contact and consume only honey bee proteins
and hydrocarbons.

4.  And there is the possibility that the mites' sensory papillae are more
sensitive to damage by OA than are those of the bees.

5.  OA-treated bees absorb some of the acid into their bodies, where it
shows up in their haemolymph (
http://revistas.inia.es/index.php/sjar/article/viewFile/270/267).  It's
possible that varroa feeding on those bees may be sensitive to this acidity.

I'd appreciate hearing any additions to the above list!

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

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