Refining Hyperthermia for Varroa Control in Honey Bee Colonies: Effects of Timing and Humidity

Commodities

• Animals: bees
• Animal Products: honey

Practices

• Animal Production: animal protection and health, parasite control
• Crop Production: beekeeping
• Pest Management: other

Honey bee colony losses over the last decade have averaged ~50% annually (1). Losses in Vermont during the 2025 beekeeping season average annual loss was 56% (2). The parasitic mite, Varroa destructor, and the viruses it vectors are among the leading causes of honeybee colony mortality in the Northeast (3). Standard practice is to use chemical miticides in colonies to reduce mite levels. While these miticides often successfully lower mites, they can also adversely affect queen and brood health. Coupled with limited effectiveness on viruses and evolving miticide resistance (4), the development of alternative mite treatment strategies is a necessity. Here we propose to build on the successful results of our previously SARE-funded research on thermal Varroa treatments by refining several important factors.

In principle, honey bees can survive higher temperatures than Varroa mites (5). By intentionally heating a colony for a period of time, mites can be killed with little to no damage to the bees (5, 6-7, 8). In our previous work, we determined the temperature and duration combinations that treat mites without excessive bee loss. We showed that hyperthermia treatment successfully lowers Varroa mites in honey bee colonies and works as well as a commercial miticide. We now hope to better understand the optimum conditions for implementing hyperthermia treatment and provide recommendations that achieve the greatest effect on mites with the least impact on bees.

We will refine our hyperthermia treatments by first evaluating the efficacy of adding humidity. Heat can be delivered more effectively under humid conditions, and in 2025 we saw evidence that added humidity increased treatment effectiveness. Second, we will evaluate treating sealed brood frames from overwintered colonies in early spring to reduce baseline mite levels under pupal cappings. By adding these two innovations, we hypothesize that we can deliver a more effective treatment with even less stress on the bees.

After collecting and analyzing data across two more beekeeping seasons, we will share results through online and in-person workshops hosted by the Vermont Beekeepers Association and other Northeast associations. We will publish our findings in scholarly articles and also in an industry journal such as the American Bee Journal to reach the greatest number of beekeepers with our practical findings.

Building on our previous findings demonstrating the potential of hyperthermia to control Varroa destructor and associated viruses, we aim to further refine this treatment approach in response to persistently high colony losses. Honey bee mortality in the Northeastern United States has averaged ~50% annually over the past decade, with recent losses in Vermont reaching 56%. Because Varroa mites are the primary driver of these losses-both through direct feeding and transmission of debilitating viruses-there is an urgent need for effective, non-chemical control strategies that improve colony health, beekeeper safety, and economic viability.

Current reliance on chemical miticides presents several limitations, including resistance development, residue accumulation in hive products, recurring costs, and incomplete control of virus-related impacts. Hyperthermia offers a promising alternative, with the potential to target mites on adult bees and within capped brood while also reducing viral loads. Additionally, it can be applied under a wider range of conditions, including during honey production, and may reduce long-term operational costs.

To advance this approach, we will refine our hyperthermia treatment tool and investigate:

1. The role of added humidity in enhancing heat transfer and improving treatment efficacy while minimizing desiccation risk to brood and adult bees.
2. The effectiveness of hyperthermia applied under brood-only conditions (in the absence of adult bees) as an early-season preventative strategy to suppress mite populations before they expand.

This work aims to optimize a practical, scalable treatment method that reduces reliance on chemical inputs, lowers costs for beekeepers, and supports more sustainable and resilient pollinator-dependent agricultural systems.