A Guide to Controlling Varroa

Varroa (Scott Bauer, USDA)

Morgan Roth

Spring is arriving in the north, and a young man’s mind thinks about romance. And varroa. There’s a nice new single-page guide that offers a quick look at integrated pest management (IPM) for the varroa beast. You can read some of the details, here, at the Entomology Today website, or read a complete paper on the topic at the Journal of Integrated Pest Management. Both pieces were written by Morgan Roth (et al.), an entomology research assistant at Virginia Polytech.

Here are a few lines from the abstract of “Biology and Management of Varroa destructor (Mesostigmata: Varroidae) in Apis mellifera (Hymenoptera: Apidae) Colonies”, which appears in the integrated pest management journal.

…overuse of synthetic acaricides in the past has led to widespread acaricide resistant V. destructor populations. The application of Integrated Pest Management (IPM) techniques is a more recent development in V. destructor control and is suggested to be more effective than only using pesticides, thereby posing fewer threats to A. mellifera colonies. When using IPM methods, informed management decisions are made based upon sampling, and cultural and mechanical controls are implemented prior to use of acaricide treatments. If acaricides are deemed necessary, they are rotated based on their mode of action, thus avoiding V. destructor resistance development.

This, of course, is relatively well-known advice. But the quality of the article, published this month, is worth your time. You can follow the historic migration of varroa from a largely benign existence on Apis cerana in Asia, to its nearly world-wide domination as a parasite that chews out bits of Apis mellifera. The paper covers biology and reproduction, current controls (synthetic and organic acaricides), non-chemical treatments, and of course, how all things fit together in the IPM model.

Here’s a bit more, from the section Soft (Organic) Acaricides:

Soft acaricide treatments have been steadily increasing in popularity, as they rarely accumulate to harmful levels in hives and bee products (Rosenkranz et al. 2010). Oxalic acid that can be sprayed, trickled, evaporated into hives, or used as crystals, is thought to be preferable for use in autumn and winter months (Rademacher and Arz 2006). Lactic acid is also used in small apiaries during the autumn and winter, is administered by spray, but is a time-consuming treatment strategy (Kraus and Ben 1994). Formic acid is administered as a fumigant, inserted into hives on saturated pads or in gel pads (Elzen et al. 2004), or in gel packs, and is best used during summer months, or during a period of the year when average daily temperatures reach 15°C (Satta et al. 2005). These organic acids all occur naturally in honey (Kraus and Ben 1994, Rademacher and Arz 2006, Gunes et al. 2017); however, high levels of formic acid vaporization can be toxic to bees, therefore, acid concentrations and hive temperatures should be monitored while treatments are being administered (Elzen et al. 2004). It is recommended that day temperatures range between 10 and 33°C when formic acid strips are in use (Honey Bee Health Coalition 2018). Despite the risks, formic acid is also the only soft acaricide that is known to kill mites in A. mellifera capped brood cells, which makes it an attractive option (Fries 1991). The modes of action for these acids are unclear, but it is suspected that oxalic and lactic acid lead to mite death via solution acidity, and formic acid is thought to eventually interfere with V. destructor metabolism and respiration (Rosenkranz et al. 2010).

Many essential oils have also been tested for use in V. destructor control, however, thyme (thymol), marjoram, sage, wintergreen, clove, and turpentine (camphor) oil, are most commonly implemented, and have been somewhat successful (Imdorf et al. 1999). These treatments may be administered as fumigants, sprays, powders, saturated absorbent materials, or gels (Mondet et al. 2011). These essential oils are believed to be effective due to their neurological effects on V. destructor (Blenau et al. 2012). Tobacco extract was also shown to be an effective acaricide, especially when used in combination with clove oil (Mahmood et al. 2014). Thymol, purchased as Apiguard gel or powder, is the most commonly used essential oil. Thymol is considered to be more effective than tau-fluvalinate, which could be due to resistance (Ahmad et al. 2013) even though it can have different effects on bees of various ages and is still ineffective on mites in bee brood (Mondet et al. 2011).

I think that the articles, in Entomology Today (a synopsis) and the Journal of Integrated Pest Management, are worth your time. They will certainly help you know your enemy and maybe even restrict the voracious vermin to destroying your neighbours’ hives, instead of your own.

About Ron Miksha

Ron Miksha is a bee ecologist working at the University of Calgary. He is also a geophysicist and does a bit of science writing and blogging. Ron has worked as a radio broadcaster, a beekeeper, and Earth scientist. (Ask him about seismic waves.) He's based in Calgary, Alberta, Canada.
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