>Dee Lusby goes wrong (in public) by emphasising small celling. What she and her followers fail to do is give due credit to their insistence on 'taking your losses' through not treating.
As far as Dee, as already pointed out, she has said for as long as I have known her (12 years or so) that it is 1/3 genetics, 1/3 natural food and 1/3 cell size.
I tried taking losses to get mite resistant bees. The all died from Varroa. I tried small cell (with new bees of course since none survived) and lost none to Varroa. You want to believe it's all genetics but that does not explain my success at all.
Not that I'm against genetics. I certainly think there are many things bees face besides Varroa and we should be raising bees that can survive these things on their own and until you stop treating you can't breed for bees who thrive without treating.