can't speak for hip, but believe they take viruses into consideration via selection of only "healthy thriving survivors" without tratment for two years...as regards variability in virulence with differing mite strains being involved, don' think anyone has gone beyond anecdotal evidence yet of such a correlation, at least to my knowledge, and it should surely be looked at for co-evolutionary host/parasite implications...as per biological controls for varroa, preliminary results with a mite parasitic/pathogenic fungus (hirsutella thompsonii) in florida are promising, and certainly deserve further study along the same lines as bacillus thuringiensis for control of wax moth and possible hymenopteran parasitoids (parasitic wasps) and nematodes as well on the small hive beetle...personally, swarms/feral hives still hold out the slim lottery-like possibility of finding survival/tolerance mechanisms by natural selection, enough so to keep on collecting and observing them over time.