Beekeepers around the world have been dealing with varroa mites for decades, and today there are a number of ways to effectively mitigate varroa. There’s no universal treatment for the mites that applies to all situations, as the ideal approach will factor in variations in mite numbers, climatic conditions, beekeeping methods, genetic resistance and economic thresholds.
Regular monitoring is essential in understanding when it’s necessary to apply control methods and evaluating the success of a treatment. There will usually be a threshold number of mites per bee at which treatment is recommended, and this may vary from place to place. See our guide to monitoring here.
Seasonality and other factors
There are a number of issues to consider when choosing when to treat against varroa, and what control to implement. In temperate climates, it’s often recommended to treat for mites in spring to help the bees through their busiest period, and again in the autumn after the last honey flow. Varroa numbers should be low coming into winter in order to increase colonies’ survival chances. Treating all the hives in an apiary simultaneously and coordinating treatment with other beekeepers in the area helps to reduce the chances of the mites quickly reinfecting treated hives.
Beekeepers also need to consider factors such as the cost of treatments, how a treatment or combination of them might affect the colony’s health and genetics, residues in hives and honey from chemicals, mites developing resistance to certain treatments, and the regulations that apply in specific regions. Using a mixture of approaches to management is often the best way to minimise the chance of mites developing resistance to any one particular treatment.
IPM - Integrated Pest Management
Integrated Pest Management is an approach that aims to avoid harm, reduce pesticide use and maintain the health of your bees. When using this approach to combat varroa, beekeepers try to reduce mite numbers primarily through cultural and mechanical controls. When chemical treatments are needed, ‘softer’ chemicals derived from natural sources are given preference, with synthetic treatments only applied versus high infestation rates.
Certain honeybees have genetic resistance to varroa mites. This can come about as a result of natural selection or selective breeding. Bees with varroa resistance have behaviours that limit mites’ reproduction, including uncapping and recapping brood cells, increased grooming, and mite-biting.
Using bees that have varroa-resistant traits can help to reduce the amount of chemical treatments needed. In South and Central America, miticides have not been widely used, and the honeybees there are believed to have greater genetic resistance to mites when compared with North American bees.
Flow has provided support for Corinne Jordan’s program to breed for varroa resistance in Australian bees using Dr Kaira Wagoner’s innovative UBO technology.
Cultural controls are techniques that reduce the mites’ reproduction.
A brood break or brood interruption occurs when the queen is not laying eggs and can disrupt the mite’s life cycle by reducing the number of available brood cells for mite reproduction. Putting the queen in a cage for 2-3 weeks provides a brood break. When requeening, a brood break can be done by delaying the introduction of the new queen for a couple of weeks. Beekeepers will sometimes use this time as an opportunity to also apply a chemical treatment if necessary, and/or use drone frames to trap mites (see below).
Foundation with small cell comb
If using foundation in your hives, you can choose to provide a smaller-sized cell comb (4.9 mm), as opposed to regular-sized cells (5.2-5.4 mm). Smaller cell comb is said to reduce the mite load as there is less space for them to reproduce, and the post-capping period is shorter, giving mites less time to reproduce.
Mechanical controls are methods that involve physically removing mites from the hive.
Trapping mites in drone brood
Mites preferentially reproduce in drone brood. Mite trapping entails adding foundation frames of drone comb to the hive as bait. Mites will preferentially lay in the drone cells which can then be culled when the larvae are 14-23 days old. The drone larvae and mites are destroyed by scraping the comb into a bin or freezing the frame. An advantage of freezing is that when you replace the frame, the bees can remove the dead drones and reuse the comb.
Screened bottom board
Using a screened bottom ensures that any mites that fall off the bees will fall out of the hive.
Some beekeepers sprinkle powdered sugar over their hive on a regular basis, in a method similar to the sugar shake used for monitoring. The sugar coating induces grooming which can dislodge mites and may help to keep mite numbers down.
While cultural and mechanical controls can be effective in suppressing mite reproduction and keeping their numbers down, there are times when chemical treatments may be necessary. If chemical controls are used, the least toxic options should be used first, with more toxic methods utilised only as a last resort.
NB: Certain chemical treatments are prohibited or restricted in some regions. Make sure to check your local regulations before applying any chemical treatments. Only use as indicated and follow all label directions and safety precautions.
Soft chemicals are derived from natural substances, they are not persistent and they do not contaminate wax or honey over the long term. These include thymol, formic acid, oxalic acid, and hop-beta acids. Soft chemicals have not been shown to negatively affect bee health, and mites have not built up resistance to these products in the same way as they have to some hard chemical treatments.
The effectiveness of these treatments can vary greatly depending on factors such as environmental conditions, time of application, method of application, and frequency of use. Some can be harmful to humans in very high concentrations.
Hard chemicals are synthetic miticides and have been widely used against varroa mites in Europe and North America. They include: Flumethrin (Bayvarol), Tau-fluvalinate, Coumaphos, and Amitraz. These chemicals can be highly effective against mites when used correctly.
Varroa mites can quickly develop resistance to hard chemicals. The compounds can also accumulate in wax and honey, which can negatively impact bee health. Beekeepers often remove their honey supers before using hard chemicals. If applying hard chemical treatments, it’s often recommended to rotate different chemicals to reduce the chances of resistance developing.