>But what is its efficacy? Last report I got was it was not too efficient
>compared to other OA methods- or have things improved?

Back in 2005 Rademacher wrote this detailed review of all the OA application methods still in use today. If you get a chance to read it you'll find the extent to which testing was done worldwide. The efficacy of each method is documented by numerous studies, many of which we have discussed. The interesting part is that they had drop results for three gas-evaporators (think ProVap type) but only one showed the same efficacy as the slow heater types (think Varrox type). So, I suspect there is something different going on with the way the vapor is applied. 



>In testing three different gas evaporators (Varrogaz, Isenring, Krüso described by
>Imdorf et al., 2004), which heat with gas burners, only Varrogaz reached mite mortality comparable
>to the Varrox electrical evaporator. Isenring and Krüso evaporators showed lower
>efficiencies, although high oxalic acid dihydrate dosages were sublimated (2.4 resp. 3 g);
>Krüso (2.4 g) was least effective with 29% mite fall (Imdorf et al., 2004).


>Oxalic acid for the control of varroosis in honey bee colonies – a review
>Eva RADEMACHER*, Marika HARZ  (2005)


https://www.apidologie.org/articles/apido/pdf/2006/01/M6010.pdf

Bill Hesbach
Cheshire CT

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