Submitted to: International Journal of Acarology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2004
Publication Date: 3/20/2005
Citation: Sammataro, D., Untalan, P., Guerro, F., Finley, J. The resistance of Varroa mites (Acari: Varroidae) to acaricides and the presence of esterase. 2005. Internat. J. Acarol. Vol. 31, No. 1. 67-74. Interpretive Summary: Varroa mites are becoming resistant to acaricide treatments used by beekeepers. We want to determine if mites were resistant to the three acaricides: fluvalinate, coumaphos and amitraz. In 2003, we surveyed mites from commercial beekeepers located in North Dakota, Florida, Arizona, California, Maine and from colonies moved between Maine and Florida as well as colonies from our laboratory in Tucson. In addition, we wanted to establish if resistant mites were using esterase to detoxify the chemicals in the acaricides. We utilized an esterase activity gel technique to see if we could visualize the presence of esterase in pesticide resistant mites. The gel technique has been used to identify esterases in resistant cattle ticks but has not been used before on Varroa. We found mites from our laboratory apiary that we tested in the spring were susceptible to all three acaricides. However, mites sampled in the late summer from our lab bees were resistant to all three acaricides. When we tested mites from five different states, all mites showed resistance to fluvalinate, coumaphos and amitraz except mites from Florida (collected in the spring). All mites that were tested for esterase using the gel technique were positive. This means that mites we tested in 2003 were resistant to all acaricides. There is increasing difficulty to find both susceptible and esterase-free mites due to not only introduction of packaged bees and queens from other states, but also to the mobility of bee colonies and adhering Varroa of mixed chemical background exposure.
Technical Abstract: Varroa mites are becoming resistant to acaricide treatments via metabolic and/or target site desensitivity. Results of a survey of mites from the Carl Hayden Bee Research Center, Tucson, Arizona and from cooperators in five locations showed that some mites were susceptible to all three acaricides in the spring of 2003, but by fall most mites were resistant. Mites were resistant to all chemicals, even from beekeepers that do not treat colonies with acaricides. Enzymes, such as esterase have been identified in some resistant mites and cattle ticks. We used esterase native activity gels to test for the presence of specific esterases which might be involved in pesticide resistance in Varroa. All mites tested had positive bands for esterase, even those exhibiting susceptibility to some acaricides. Based on the differences between the esterase activity gel profile of the susceptible and cross-resistant V. destructor, it is possible than an esterase-mediated resistance mechanism is operative in the population of the mites we analyzed. However, a combination of other resistance mechanisms may be present which make the esterase activity gel method not reliable for use in identifying Varroa mites with multiple resistances.