Varroa Mite Monitoring & Control: A Beekeeper’s Guide to Healthy Hives
Varroa destructor is the most serious threat to honey bee colonies today. These parasitic mites feed on the fat bodies of bees and spread deadly viruses like Deformed Wing Virus (DWV). Effective monitoring and control of Varroa mites is essential for keeping your bees healthy and your honey harvest strong.
Monitoring Varroa Mite Levels
Monitoring mite levels helps beekeepers catch infestations early and treat before they cause serious harm. The most accurate monitoring method is the alcohol wash, where about 300 bees are collected from the hive and shaken with alcohol to dislodge and count the mites. A gentler alternative is the sugar shake, which uses powdered sugar and allows the bees to survive, though it is generally less accurate. Sticky boards, placed under screened bottom boards, catch mites that fall naturally and can provide a passive but useful assessment over time. It is important to monitor regularly throughout the beekeeping season, especially in the spring, summer, and fall. Spring monitoring helps detect early infestations before they gain traction. Summer is typically the peak season for mite buildup, and fall monitoring is crucial for ensuring colonies go into winter with low mite loads. Treatment is typically recommended when mite levels exceed three percent, or roughly nine mites per 300 bees.
Integrated Pest Management (IPM) Strategies
An effective approach to controlling Varroa mites relies on Integrated Pest Management (IPM), which combines multiple strategies to minimize chemical use and slow resistance development. Cultural practices like drone brood removal and brood breaks help disrupt mite reproduction. Using screened bottom boards can aid in natural mite fall and improve ventilation. Additionally, softer treatment options such as thymol, oxalic acid, and essential oils can be used as part of a rotation or when mite levels are moderate. Mechanical controls like improving hive insulation and ventilation also contribute to an environment less favorable to mite reproduction, complementing the other tactics in an IPM strategy.
Amitraz: Once a Staple, Now at Risk
Amitraz, commonly sold under the brand name Apivar, has long been a go-to miticide for treating Varroa infestations. However, recent research has raised serious concerns about its continued effectiveness. Studies from the USDA have found that amitraz-resistant mites are now present in many colonies suffering large-scale collapse. These mites carry specific genetic mutations, that are directly linked to treatment failure. A significant Canadian study revealed that 90 percent of mites tested in Alberta carried these mutations, indicating how widespread resistance has become. As these resistant strains of Varroa mites spread, the reliability of amitraz as a treatment option is diminishing, and beekeepers who rely solely on it may face increasing colony losses.
Smarter Treatment Approaches
To preserve the effectiveness of amitraz and other miticides, beekeepers must adopt smarter treatment approaches. Rotating chemical treatments is essential to prevent mites from developing resistance. Alternating between amitraz, oxalic acid, formic acid, and thymol helps reduce selective pressure on the mites. Treating only when monitoring shows it is necessary is a key principle of IPM, as unnecessary or routine use of treatments accelerates resistance. Some research indicates that resistance to amitraz may decline after a one-to-two-year break from use, likely due to the chemical’s low persistence in the hive environment. However, this is not a guaranteed outcome, and relying on this alone is risky.
Research Highlights
The latest research confirms that Varroa mites are a primary driver of widespread viral infections in honey bee colonies. Resistance to amitraz is now directly tied to specific genetic mutations, and the discovery of new mutations continues to highlight the mite’s adaptability. Genetic surveillance efforts are ongoing, and they emphasize the need for diversified treatment plans and the development of new miticides. While some believe amitraz could regain effectiveness if rotated out for a period, the science points toward the need for comprehensive and proactive management strategies that do not rely heavily on any single chemical treatment.
Your Seasonal Varroa Plan
A seasonal plan is essential for keeping mite levels under control throughout the year. In the spring, monitoring mite levels and assessing colony strength set the stage for the rest of the season. Summer is the time when mite populations can explode, so it is important to stay vigilant and implement control methods like drone brood removal or soft treatments if necessary. Fall is a critical period for treatment, as ensuring low mite loads before winter is key to colony survival. This is also the time to consider combining weak colonies and evaluating queens. During winter, while treatments are typically paused, beekeepers should reflect on the past season and plan for genetic improvements and treatment strategies for the upcoming year.
Controlling Varroa mites is no longer about one-size-fits-all solutions. With the rise of amitraz resistance and the increasing threat from viruses transmitted by these mites, it is more important than ever to monitor mite levels carefully, treat only when necessary, and rotate treatments to reduce resistance pressure. By following an Integrated Pest Management strategy and staying informed on the latest research, beekeepers can protect their colonies and enjoy healthier, more productive bees. The key is to stay vigilant, adaptive, and science-driven in your approach to Varroa mite control.