> Well, I'd like to report that after doing mite washes 
> yesterday (this after a 2nd regimen of 3 more OA 
> vaporizations) that my mite levels are unchanged 
> in several hives.

The problem may be your methodology and/or equipment.

The "oxalic vaporizers" I've seen have been woefully inadequate for the
task, in that they have no temperature regulation other than the "heat sink"
of their own metal mass.  This means "overshoot", as the amount of OA is not
large in terms of mass, and the battery will keep supplying current long
after the heating element has started to glow red.

The difference between sublimation of the solid to a gas (which you want),
and boiling/burning (which you don't want) is the difference between an
effective treatment and a waste of time reminiscent of the "Food Grade
Mineral Oil Fogging" fad/cult of about a decade ago.

The problem is that tight temperature regulation does not come cheap.  I
built one, but I had spare parts lying around.  I remember that one of the
provincial apiarists in Canada tried to market a thermostatically-controlled
vaporizer, and was unable to attract much interest, evincing a profound lack
of schooling in chemistry among beekeepers.

The work that Marion Ellis (U Nebraska) did led to the conclusion that
"dribbling" was more reliable than "fogging" in terms of varroa control,
with the understanding that oxalic would be very bad for any open brood.
I've dribbled oxalic only after the hive is broodless, as it, like all
varroa controls, works best when there is no sealed brood to harbor varroa.

A vaporizer satisfies that deep-seated need to feel that one is wielding a
"weapon" against varroa, much the same impulse that the FGMO fogger
fulfilled.  But dribbling may give far better results in terms of actual
varroa control, despite the unfortunately-impotent-sounding name, so I use
large-animal veterinary syringes from the Agway to dispense the oxalic
solution, as this at least allows one to feel that one is administering
"medicine" to the hives, and it makes for a handy way to measure out the
correct number of milliliters of solution.


 

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