Varroa Treatments that Work in Fall, Winter, Spring, and Summer

I just returned to the USA from a lovely year-long sabbatical in Australia. It was a fairly dramatic year for Australian beekeepers; varroa invaded a few months before I arrived, the government innitially tried to eradicate the mite by euthanizing all hives discovered to be infested, then gave up and decided it was hopeless. In other words, varroa is now comfortably established on every inhabited continent on earth, including Australia.
I’ve spent much of the past year speaking with Australian beekeepers about how to control varroa. They’re somewhere between resigned and terrified. But have no fear, dear Aussies, varroa can be controlled! The rest of the world, including the USA, has been managing varroa for decades.
But it pays to be knowledgeable when controlling varroa. Some treatments are best when brood is present while others are best when brood is absent. Some treatments pose a risk to colonies during hot summer months while others can be used year-round. In addition, overuse of some chemistries has led to resistance, which reduces treatment efficacy.
So, which common chemical treatments are best for tamping down varroa levels and keeping them down post-treatment? Are different treatments more effective than others at different times of the year? These are the topics for the seventy-eighth Notes from the Lab, where I summarize “Evaluating the seasonal efficacy of commonly used chemical treatments on Varroa destructor (Mesostigmata: Varroidae) population resurgence in honey bee colonies,” published in the Journal of Apicultural Research [2024] and written by Cameron Jack and colleagues at the University of Florida Honey Bee Research and Extension Lab.
Jack and colleagues actually conducted two studies. First, in fall 2014, they established 40 colonies at an apiary near the University of Florida campus in Gainesville. At the start of the trial, all colonies were equalized to ensure they were similar size (number of bees, area of brood), strength (honey and pollen stores, absence of disease), and varroa infestation levels. Then each received one of four treatments: Apiguard (active ingredient thymol), Apistan (tau-fluvalinate), Apivar (amitraz), or CheckMite+ (coumaphos). All treatments were administered according to product labels, and mite infestation levels were assessed for each colony at six time points: project initiation (i.e., pre-treatment), end of treatment (i.e., when the product was removed), and at one, two, four, and six months post-treatment.
The second study was larger. Between October 2020 and January 2022, 412 colonies were maintained at the University of Florida’s Beef Research Unit. The goal of the second study was to understand seasonal treatment efficacy throughout an entire year, so colonies were repeatedly enrolled in seasonal trials. “Fall” season began in October 2020, “winter” began in January 2021, “spring” began in May 2021, and “summer” began in August 2021.
Before the start of each seasonal trial, colonies were equalized in a manner identical to the first study, then they received one of eight treatments: Apiguard (thymol), Apistan (tau-fluvalinate), Apivar (amitraz), CheckMite+ (coumaphos), MAQS (formic acid), oxalic acid (OA) dribble, OA shop towels, and amitraz (shop towels soaked in Bovitraz). All treatments were administered according to product labels or common beekeeper use patterns (see details following the references section).
Not all colonies were included in each seasonal trial, but at least 10 colonies were tested for each treatment in each season. Mite infestation levels were determined monthly until average levels of an individual treatment group reached the economic threshold of 3 mites per 100 adult honey bees, at which time the treatment group was removed from the study.
So, what did they find? Did the first study (the fall 2014 only study) reveal any differences in varroa post-treatment? Yes. As can be seen in Figure 1, three of the treatments (Apiguard, Apistan, and Apivar) were more effective at…