Oh, but they do ... I think.

I'm an irregular reader of Beebase. They've got an active "treatment-free" sub-forum to list their colony losses ... er, I mean describe their experience in achieving mite-free nirvana.

The ever-dependable JWChesnut has recently posted a link to study from the Louisiana USDA-ARS (unfortunate, but that's acronyms for you) team comparing a healthy whack of Amitraz with a light-touch IPM strategy ... essentially, sugar dusting, some drone brood removal and OMF's. Perhaps unsurprisingly, the IPM strategy was indistinguishable in terms of impact on mite numbers to truly treatment-free colonies, with mite levels reaching 15-20% by autumn. Amitraz-treated colonies had low, but certainly not insignificant, mite levels throughout ... but they were treated with Amitraz for over 100 days of the study period (mid-May to late October).

I've not used Amitraz but was surprised that 2 x 56 day treatments with the drug, whilst being dramatically better than no treatment, didn't reduce mite levels much below about 4%. Is this typical?