When managing hives that are carrying varroa, it is inevitable that beekeepers will, at some point, have to use chemical treatments. But where possible, treatment with chemicals should be avoided and a range of non-chemical treatments and practices employed — as part of an integrated pest management (IPM) strategy — to keep mite infestation below a level that becomes detrimental to the bees.
Chemical treatments for varroa fall into two broad categories — synthetic and naturally derived (also known as non-synthetic or organic). There are advantages and disadvantages to both categories.
It is important that safety guidelines are adhered to when using chemical treatments. Both synthetic and naturally derived acaricides can be harmful to bees and humans if used incorrectly.
Naturally derived acaricides
Naturally derived acaricides are derived from natural sources and include organic acids and plant essential oils such as oxalic acid, formic acid and the plant essential oil thymol (extracted from thyme) (Table 1). They are commercially available as the active ingredients in several different products.
Formic acid is generally applied via plastic strips, while oxalic acid can be applied via trickling, where the oxalic acid is dissolved in sugar syrup and trickled between frames or via sublimation, where it is heated to 160°C and spread through the hive as vapour. Thymol can be applied as strips, or in trays above the frames where it eventually vapourises.
Naturally derived acaricides tend to have lower efficacy than synthetics and require follow up treatments or should be used in conjunction with non-chemical treatment. Their major advantage is that they target multiple systems within the mite, thus reducing the risk of resistance developing. When used in conjunction with non-chemical treatments, they are highly effective at keeping varroa below a level where it can do economic damage.
Table 1. Naturally derived varroa treatments, only some are approved for use in Australia*
* Not all of these products are registered for use in Australia| Active ingredient | Commercial products | Administration | Pros | Cons |
|---|---|---|---|---|
| Formic acid | MAQS FormicPro Nassenheider Professional Varterminator | Gel strips added to the brood nest | Can kill both mites on adult bees and mites within the brood cells. | An irritant to humans and must be handled with gloves. Causes some adult bee mortality. |
| Oxalic acid | Oxivar Oxybee Api-Bioxal Dany’s Bienenwohl powder | Trickling or sublimation | No evidence of mites becoming resistant. Can kill over 90% of mites. As sublimation does not require hives to be opened and oxalic acid is best used during broodless periods, it is an ideal winter treatment. | Requires specialist equipment to administer, which can be costly. Can be lethal to open brood, so should not be applied to colonies with larvae. Can be toxic to humans. PPE must be worn when handling it, particularly if administered via sublimation. |
| Hop beta acids | HopGuard | Strips hung between frames | Can be applied to both package bees and colonies, even in summer when temperatures are high. Non-toxic to humans and bees. | Effectiveness varies. While hop beta acids can kill up to 90% of mites, studies report a wide range of mite mortality. |
| Thymol | Apiguard Apilife Var Thymovar | Strips or trays | Users can expect about 80% of mites to be killed if used correctly. Mites are unlikely to become resistant | Thymol is an irritant and must be handled with gloves. Can taint honey, so honey must be harvested before treatment. Can cause some brood mortality if applied at high temperatures. |
Synthetic acaricides
Commonly used active ingredients in synthetic acaricides include amitraz, coumaphos, flumethrin and tau-fluvalinate (Table 2). The chemicals work by interfering with the mite’s nervous system and cellular functioning.
There are a few different ways to apply synthetic acaricides depending on the product, but typically a plastic strip impregnated with the chemical is placed between frames in the brood nest. The number of strips and the time they need to be left in the hive will vary depending on the product. Bees contact the strip and distribute the acaricide throughout the hive as they move around.
Synthetic acaricides are easy to use and are highly effective in varroa populations not previously exposed to the chemicals. Mortality rates in mites are typically greater than 90%.
But mite populations can develop resistance to them within a few years, decreasing their effectiveness. Resistance arises due to genetic mutations in key genes involved in the acaricide mode of action. Most synthetic acaricides interact with mites via a single, specific target, meaning resistance could develop easily due to a single mutation. In some cases, mite populations remain resistant for years after the chemical is no longer in use, rendering the chemical useless within a couple of seasons of treatment.
Table 2. Synthetic varroa treatments, only some are approved for use in Australia*
* Not all of these products are registered for use in Australia| Active ingredient | Commercial products | Administration | Pros | Cons |
|---|---|---|---|---|
| Amitraz | Apivar Apitraz | Plastic strips | Highly effective, killing 75-90% of varroa in a hive. Easy to administer. Mites remain susceptible to amitraz for longer than other synthetic compounds. Does not persist in honey or wax. | High doses can negatively impact brood survival. Mite resistance is growing. Must be used in rotation with other chemicals. |
| Coumaphos | CheckMite | Plastic strips | Easy to administer. Highly effective in unexposed populations. | May be harmful to larvae or adult bees. Varroa populations worldwide are now largely resistant to this compound. Must be used in rotation with other chemicals. |
| Flumethrin | Bayvarol PolyVar Yellow | Plastic strips | Easy to administer. Highly effective in unexposed populations. Low impact on larvae or adult bees. | Effectiveness varies due to increasing mite resistance. Must be used in rotation with other chemicals |
| Tau- Fluvalinate | Apistan | Plastic strips | Easy to administer. Highly effective in unexposed populations. | Resistance develops quickly. Apistan kills 96% of mites in the first year of use but this drops to 76% by the third year. Must be used in rotation with other chemicals. Cannot be administered until after honey is removed. Can negatively affect adult bee learning and memory. |
What should I use on my bees?
Only use chemicals that have been granted permits. As with all chemical applications, it is important to consider all aspects of use, including safety to beekeepers and bees, chemical residues in hive products, application frequency, and treatment timing.
Check mite loads before application to determine if their use is warranted, and check mite loads after treatment to ensure it has been effective.
Treatments
For a list of treatments currently approved or in the process of approval for use in Australia please see the AHBIC website.
More information
- AgriFutures on Air – Varroa Expert Interview Series: Topic 6 – Chemicals for treating varroa – organic or synthetic?
Acknowledgements
- Holmes, Gerdts, Grassl, Mikeheyev, Roberts, Remnant, Chapman (2024) Resilient beekeeping in the face of Varroa. AgriFutures Australia.
- https://honeybee.org.au/wp-content/uploads/2024/07/AGF575-Chemicals-for-treating-Varroa-S1V2-1.pdf
- Dai et al (2018) Chronic toxicity of amitraz, coumaphos and fluvalinate to Apis mellifera L. larvae reared in vitro. Sci. Rep. 8, 5635
- Degrandi-Hoffman et al (2012) The effects of beta acids from hops (Humulus lupulus) on mortality of Varroa destructor (Acari: Varroidae). Exp. Appl. Acarol. 58, 407–421
- Frost et al (2013) Effects of fluvalinate on honey bee learning, memory, responsiveness to sucrose, and survival. J. Exp. Biol. 216, 2931–2938
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- Stainton (2022) Varroa Management: A Practical Guide on how to Manage Varroa Mites in Honey Bee Colonies. Northern Bee Books
- Tomé et al (2020) Frequently encountered pesticides can cause multiple disorders in developing worker honey bees. Environ. Pollut. 256, 113420
- This article was peer reviewed by Emily Remnant and Nadine Chapman.
