Looked at my notes on this... there's data in them thar hills.

An ad-hoc workshop by Marion Ellis on Oxalic dribbling took place at EAS in
the early 2000s, when he was working to get EPA approval.  (2002?  2005? I
forget)  He stressed that Oxalic was toxic to both varroa and bees, and that
very careful measuring and dosing would be key to making it all work.

Marion's later EAA paper listed the toxicity at various doses for both bees
and mites, so there is inevitable bee mortality when using oxalic to kill
mites, and the dose matters.  So, ideally, the bees have a certain tolerable
level in their bodies as a result of feeding, and the mites are poisoned
when the feed on the bees.

http://doi.org/10.1007/s10493-009-9240-8

Full text here, as paywalls suck, as does their security:
https://drive.google.com/file/d/15YA2qVN-mssqXtoMm9Fy5Ry2_KC2sVye/view?usp=s
haring
https://tinyurl.com/3vhcn4xa

When vaporizing, there is an "acute contact" dose and the potential of an
oral dose for the bees.  One would think that the bees might lick enough up
when cleaning to get a toxic dose, but no one has quantified the bee
toxicity to my knowledge, other than to hand-wave it away as "low", even
when repeated vaporization is practiced.  It is clear that the bees can
handle whatever mortality they suffer, and that it is not as high as an
over-dosed dribble treatment.

https://core.ac.uk/download/pdf/188116453.pdf


One piece of low-hanging fruit that has been in front of our noses since the
late 1990s is humidity, but I do not know how one might make a more damp
brood chamber than the bees like while still keeping the hive "in the yard".
But high humidity reduces varroa reproduction significantly - at 59%-68%
relative humidity, 53% of mites reproduced. At 79%-85% relative humidity
only 2% of the mites reproduced.  (But oppressive 80% humidity is common at
NAS Pensacola, do beekeepers near there have less varroa issues?  I have not
heard anyone say so.)

"High Humidity in the Honey Bee (Apis mellifera L.) Brood Nest Limits
Reproduction of the Parasitic Mite Varroa..."
https://doi.org/10.1007/s001140050382

Full text here:
https://drive.google.com/file/d/1gGPD9wA1VlB_M93adc9cULaCrzbI_Ol3/view?usp=s
haring
https://tinyurl.com/3he2nf89

Don't be put off by their misidentification of varroa as "jacobsoni" -
everyone did that for years. Somehow, everyone missed the gross morphology.



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