>I have never seen anything to indicate that OA evaporation harms the bees,
but reason insists that coating bees with acid has to have some deleterious
effects.

Best that I can tell, Allen, is that OA has a transient effect upon the bee
hemolymph pH and gut epithelial cells.  Bees exhibit a generic gut respose
to exposure to toxins--they shed the epithelial cells lining the gut,
through a process of intentional cell death termed apoptosis.  Those cells
are then quickly replaced.  Haemolymph pH also soon returns to normal.
 However, there are some European studies that suggest some degree of
colony setback due to OA treatment.

I personally don't notice any substantial degree of setback due to a single
fall/winter OA dribble, nor multiple summer dribbles.  I can't speak to
vapor.

>Has anyone here any data on the effects on wintering or spring performance
of colonies repeatedly dosed with OA vapour?

When I asked Heilyser this question a few years ago, they sent me some data
suggesting that multiple vaporizations were well tolerated.

>The exceptions from that average are what makes understanding and applying
'soft' treatments difficult to predict.

Boy, you got that right!  I'm freshly returned from the Oregon State
convention, at which I heard anecdotal reports of serious issues with both
Apiguard gel, and MAQS--neither of which I've experienced to any extent,
nor did the state apiarist, Ramesh Sagili, when he tried to replicate in
limited field trials.  As you say, the exceptions to the average can be
surprising, to say the least!

Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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