Oxalic acid has a strong short-term effect in bees.  When applied in syrup
(dribble, spray, or feeder) it causes short-term apoptosis of gut cells and
a temporary drop in haemolymph pH.

I haven't seen data on what happens when applied as vapor, which results in
the formation of jillions of tiny crystals of oxalic acid condensing on all
hive surfaces, including the bees' bodies.  I'm not sure whether those
crystals are sharp enough to penetrate the soft integument at the joints.
But they would likely be consumed during grooming.

There's a small margin of safety with oxalic.  It's easy to overdose your
bees.

As far a bees "being back to normal" after oxalic vaporization, I'd
strongly suspect that the effects of treatment actually last for days.
-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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