This study is recent and may be of use to you:
"Detection of amitraz resistance and reduced treatment efficacy in the Varroa Mite, Varroa destructor, within commercial beekeeping operations"
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0227264
"Detection of amitraz resistance and reduced treatment efficacy in the Varroa Mite, Varroa destructor, within commercial beekeeping operations"
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0227264