What's the Buzz with ATTTA #89

Thursday, 10 March 2022

Varroa mite resistance to synthetic acaricides is a prevalent topic in current Canadian beekeeping. In a recent blog, we reviewed a Manitoba news article released this February regarding concern over varroa mite resistance to the popular miticide Apivar. This week, we are enthusiastic to report that there is newly published research available on the topic of miticidal efficacy in Canada (Morfin et al. 2022). Read on to learn what researchers in Ontario have reported about their findings and what this means for Atlantic beekeepers.

Ontario miticide surveillance 

In the late summer and early fall of 2019, Ontario researchers collected samples of honey bees and parasitic varroa mites from 22 colonies across 12 apiaries in the province. They then tested the mite populations against three different synthetic acaracides registered for use in Canada as varroa mite treatments, amitraz, flumethrin, and tau-fluvalinate, the active ingredients in the familiar products Apivar™, Apistan®, and Bayvarol®, respectively. The results of these efficacy tests found amitraz to cause 92% mite mortality, followed by tau-fluvalinate at 78% mortality and flumethrin at 72%, suggesting that amitraz is mostly effective and tau-fluvalinate and flumethrin are only minimally effective. 

(Figure from Morfin et al. 2022)

Mite resistance to Apistan has been documented previously and was expected in this trial. However, the researchers did not expect such a low efficacy from Bayvarol. The data collected by this research suggests that mites are becoming resistant to Bayvarol, as of 2019 when the samples were collected. Another result which stood out was the variation in efficacy between regions and apiaries. All of this supports the importance of periodic efficacy testing as a critical part of varroa mite management. Effectiveness of a treatment when it is first released cannot be expected to persist indefinitely and tracking regional changes is important for local management. These results will provide important benchmark data for future efficacy testing in Ontario apiaries and is relevant to beekeepers across Canada. 

ATTTA performed similar efficacy testing in the Atlantic provinces in the summer of 2017 and spring and summer of 2018 (Olmstead et al. 2019). In this study, the mite mortality of Apivar was 99.8% and mortality of Bayvarol was 96.5%. Apistan was not included. The more recent publication from Ontario demonstrates a lower efficacy for both Apivar and Bayvarol. The difference between mite mortality of 99.8% and 92%, as seen in Apivar, may not seem very significant but given the reproductive capacity of varroa mites, the impact can be profound. A population of varroa mites has the potential to double every four weeks during the brood rearing period (Trodtfeld, n.d.). Considering this, if a colony has 100 mites in March and is treated with a miticide of 99.8% efficacy, by August the colony will have 32 mites. On the other hand, if those 100 mites are treated with a miticide of 92% efficacy, the population will reach 256 by August! Given the reduced efficacy of Bayvarol between these two studies, the difference in mite populations for a hive treated with Bayvarol would be even more dramatic. 

The new findings published about acaracide efficacy in Ontario are important for all beekeepers in the fight against varroa mites and provide important benchmark data for future efficacy testing. ATTTA hopes to investigate this further in the coming field season and compare updated results against those from 2017 and 2018. For individual beekeepers, testing your own mite populations before and after treatments of any kind is critical to controlling varroa populations and realizing treatment success within your own colonies.   

Morfin, Nuria, Devan Rawn, Tatiana Petukhova, Paul Kozak, Les Eccles, Jim Chaput, Tim Pasma, and Ernesto Guzman-Novoa. 2022. “Surveillance of Synthetic Acaricide Efficacy against Varroa Destructor in Ontario, Canada.” The Canadian Entomologist 154: e17. https://doi.org/10.4039/tce.2022.4.

Olmstead, Sawyer, Cameron Menzies, Robyn McCallum, and Kathleen Glasgow. 2019. “Apivar® and Bayvarol® Suppress Varroa Mites in Honey Bee Colonies in Canadian Maritime Provinces,” 4.

Trodtfeld, Peter. n.d. “The Varroa Mite - a Deadly and Dangerous Parasite.” Bayer CropScience AG. https://static1.squarespace.com/static/5b4413869772ae5b390f1a56/t/5db60247c081ef63503c64f7/1572209250465/The_Varroa_Mite+%281%29.pdf.

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