Temperature, strip age, exposure surface area affect the outcomes of testing for amitraz resistance in Varroa destructor

Authors: Rinkevich, Frank

Submitted to: Journal of Apicultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2023
Publication Date: 2/16/2024
Citation: Rinkevich Jr, F.D. 2024. Temperature, strip age, exposure surface area affect the outcomes of testing for amitraz resistance in Varroa destructor. Journal of Apicultural Research. https://doi.org/10.1080/00218839.2024.2314420.
DOI: https://doi.org/10.1080/00218839.2024.2314420

Interpretive Summary: Amitraz resistance is Varroa is an important issue facing beekeepers across the globe. Apivar is a registered miticide that contains amitraz as the active ingredient. The Apivar Effiacy Test uses Apivar to assess the levels of amitraz resistance in Varroa mites, which are the major cause of poor honey bee colony health. While this test is a reliable indicator of amitraz resistant Varroa, we explored some factors that may affect the outcomes of the experiment. Control mortality is significantly increased at temperatures >30C. Apivar efficacy declines <20C due to reduced amitraz toxicity at lower temperatures. Under standard conditions, there is 32cm2 of Apivar strip. The effects of surface area on Apivar efficacy was investigated with squares with 64, 32, 16, or 8cm2 of area. Apivar efficacy was faster and more efficacious with increased Apivar surface area. We tested the effects of stripe age and found that there was no difference in strips age when stored under standard conditions. Strips that were reused after placement in the colony had low Apivar efficacy. These results show that the Apivar efficacy test should be performed 20-30C for consistent results, amitraz is less toxic at low temperatures, the difference in exposed surface area helps translate data from previous methods that used smaller exposed surface area, and Apivar remains active after expiration dates.

Technical Abstract: The Apivar efficacy test is a new method that allows for rapid evaluation of amitraz resistance in Varroa. Understanding how variables in the experimental set up is critical for collecting consistent data that is comparable among experiments. Apivar efficacy tests were conducted at temperatures from 10-35C which showed high control efficacy at high temperatures and reduced Apivar efficacy at low temperatures. These results are due to thermotolerance of Varroa and reduced amitraz toxicity at low temperatures. Packages of Apivar that were manufactured at different dates were compared. Apivar strips that were more than 9 years old showed comparable efficacy to recently manufactured strips. Apivar strips that were reused after being placed in the colony showed low and variable Apivar efficacy and should be avoided. Changing the surface area of the Apivar square used the test showed a positive effect surface area on the rate and efficaciousness of the Apivar Efficacy test. This is important to make comparisons of the Apivar Effiacy test to previous methods that used smaller surface area of Apivar strips. These results show that the Apivar efficacy test should be performed 20-30C for consistent results, amitraz is less toxic at low temperatures, the difference in exposed surface area helps translate data from previous methods that used smaller exposed surface area, and Apivar remains active after expiration dates. The influence of these factors on the reliability and reproducibility of the Apivar efficacy test in monitoring for amitraz resistance in Varroa is discussed.