Submitted to: The Speedy Bee
Publication Type: Trade Journal
Publication Acceptance Date: November 20, 2001
Publication Date: N/A
Interpretive Summary: Honey bee colonies cannot be maintained in the U.S. without some form of chemical treatment to control the parasitic mite, Varroa. A pesticide impregnated strip marketed as Checkmite+ is currently the only effective treatment. A commercial beekeeping operation in Maine, however, was shown to have mites that appear resistant to treatment with Checkmite+. This information is essential to U.S. beekeepers and to State apiary services that design mite control strategies.
The U.S. beekeeping industry has limited compounds to control the parasitic mite, Varroa. One of these compounds, coumaphos, marketed as CheckMite+, has recently been found to provide ineffective Varroa control in a single commercial beekeeping operation in Maine. The addition of 2 or 4 new CheckMite+ strips to these colonies did not result in increased mite drop while the addition of 2 Apistan (an alternative compound) strips resulted in a 10-fold increase in mite numbers. Additionally, a field assay using coumaphos showed only 13.4% mite mortality in Maine but a 93% mortality rate with mites in Maryland. The finding of high mite populations after 25 days of CheckMite+ treatment, the colony level tests with different control compounds, and field assay differences in mite mortality are all indicative of mite resistance to coumaphos. Based on these results, we feel it prudent that beekeepers use some means of assessing their mite populations before and especially following treatment with CheckMite+. The appearance of mites resistant to coumaphos in only three years of use is disturbing in light of the limited control alternatives. We hope that coumaphos-resistant Varroa are not widespread and that we can prolong the use of all control products by using rotation schemes, resistant stocks of bees, and alternative control measures.