Technical Abstract: Beekeepers have relied heavily upon synthetic compounds to control the parasitic mite Varroa. One of these products, CheckMite+, was recently been found to provide ineffective Varroa control in limited areas of the U. S. In the current study we tested mite populations in three states to both further document resistance and to develop a field assay to detect coumaphos-resistant mites. We tested a single commercial beekeeping operation in Maine and compared the mites found in forty colonies using an ether roll method to the mites found on sticky boards after 24 hours of treatment with either Apistan or Checkmite+. The addition of 2 or 4 new CheckMite+ strips did not result in increased mite drop over twenty-four hours when compared to natural mite drop. In contrast, the addition of 2 Apistan strips resulted in a near10-fold increase in mite numbers compared to natural mite drop. A field assay (modified from one used to detect fluvalinate resistance) using coumaphos, the active ingredient in Checkmite+, was conducted on these colonies and the mites on bees in Maine exhibited only 13% mortality on average while mites in Beltsville, Maryland exhibited on average 93% mortality using the coumaphos field assay under similar conditions. Additional testing of the assay in two apiaries in Florida yielded mite mortality averages of 80% and 6.8%. We would encourage beekeepers to use the assay periodically before mite treatments are applied to test for resistance to both Apistan and Checkmite+ and thus insure an effective treatment is being applied.