Detection of amitraz resistance and reduced Apivar® efficacy in the Varroa mite, Varroa destructor, in commercial beekeeping operations

Authors: Rinkevich, Frank

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2020
Publication Date: 1/17/2020
Citation: Rinkevich Jr, F.D. 2020. Detection of amitraz resistance and reduced Apivar® efficacy in the Varroa mite, Varroa destructor, in commercial beekeeping operations. PLoS One. 1-12. https://doi.org/10.1371/journal.pone.0227264.
DOI: https://doi.org/10.1371/journal.pone.0227264

Interpretive Summary: Varroa infestation is responsible for an overwhelming majority of honey bee colony losses in commercial beekeeping operations. Due to these dire consequences, beekeepers have used many types of chemicals to control Varroa populations. Amitraz is widely used to effectively control Varroa. However, conversations with beekeepers suggest Varroa may be becoming resistant to amitraz. We evaluated amitraz resistance in commercial beekeeping operations using amitraz vial bioassays as well as a field efficacy test. Significant amitraz resistance was only detected in 2 commercial beekeeping operations so amitraz remains rare. There was significant agreement with both tests for amitraz resistance, thus showing that monitoring for resistance could easily be implemented in a normal Varroa monitoring program. It appears that amitraz use alone cannot account for amitraz resistance in Varroa, so much more data on differences in operational use needs to be collected. This research hopes to establish a Varroa resistance monitoring program over the entire country in order to detect and mitigate miticide resistance in Varroa.

Technical Abstract: The Varroa mite (Varroa destructor) and the associated viruses it transmits are responsible for most instances of honey bee colony losses in the United States. As such, commercial beekeepers utilize miticides to control Varroa populations. Widespread resistance has developed to the miticides fluvalinate and coumaphos. However, Varroa has largely maintained susceptibility to amitraz despite a long and extensive use history. Anecdotal reports of reduced amitraz effectiveness has been a widely discussed contemporary issue among commercial beekeepers. Amitraz resistance was measured by in vitro bioassays with technical amitraz as well as in Apivar® efficacy tests in commercial beekeeping operations in Louisiana, New York, and South Dakota with a long history of amitraz use for Varroa control. This research shows that amitraz remains an effective Varroa control product in many operations, which is similar to most other reports on amitraz sensitivity to this point. However, the remaining apiaries displayed a range of amitraz resistance no resistance to very little resistance to high resistance that resulted in Varroa control failure. The resistance ratios from the in vitro amitraz bioassays were correlated with reduced Apivar® efficacy, demonstrating bona fide cases of Varroa control failures due to amitraz resistance. The discussion focuses around developing amitraz resistance monitoring protocols and establishing a resistance monitoring network to ensure the sustainability of miticide use for Varroa control in commercial beekeeping operations.