Oxalic Acid Treatment Table
Update April 2020: Oxalic acid will react with the calcium carbonate in hard water to form a precipitate of calcium oxalate, which you may see as a fine white layer on the bottom of the container. But this isn’t really something to worry about. The “hardest” water contains around 200 mg of calcium carbonate per liter. For an OA dribble, you use around 35 grams of OA per liter. The 200 mg of carbonate in that liter would neutralize only a tiny portion of the OA.
Table reworked and updated January 16, 2018.
You can download a printable pdf doc of the table at the link below (Note: the above table does not include updates for 2019).
Oxalic acid treatment table 2018
It is critical to mix and apply oxalic dribble correctly (5 mL between each frame of bees), or you risk seriously harming your bees! Be sure to read:
https://scientificbeekeeping.com/oxalic-acid-questions-answers-and-more-questions-part-1-of-2-parts/
https://scientificbeekeeping.com/the-learning-curve-part-3-the-natural-miticides/
https://scientificbeekeeping.com/oxalic-dribble-tips/
https://scientificbeekeeping.com/oxalic-acid-powerpoint-presentation/
Update January 17, 2019: We’ve experimented with using 40% v:v glycerin in water instead of sugar syrup. One possible advantage is that bees don’t like the taste of glycerin, and may thus be less likely to lick up the acid. The glycerin also helps the OA to adhere to the bees’ bodies for a longer period of time. This is still an experimental treatment, but we’ve used it on 1500 hives, and have been happy with the results. This application method is not currently registered for use in the United States. Some formulas below (apologies for errors in previous updates).
Update 15 July 2019: A recent study by Toomema (https://doi.org/10.1080/00218839.2018.1486695), suggests that the oxalic dribble can be equally effective if a more dilute solution of OA in water alone (5 g OA dihydrate/1 L water) is applied at the greater rate of 20 mL/comb space of bees, rather than 5 mL. The above dose applies about half as much OA to the bees, but the greater amount of solution likely results in better dispersal. Toomema also recommends adding 1.2 g* of thymol per liter of heated solution, and then applying only 15 mL/comb space. Adding thymol caused irritation to the mites (and bees) and increases efficacy, but may cause additional adverse effects to the bees.
*Note that the solubility of thymol in water is only 0.9 g/L at 20°C, so some thymol would be expected to precipitate out as the syrup cooled. The point is that only a small amount of thymol will ever dissolve in sugar syrup.
Please note that in the table below, the recipes are for weight: volume (w:v) formulas, for anhydrous oxalic acid, following the standard nomenclature used by European researchers. Anhydrous OA has a molecular weight of only 71.42% of that of the common oxalic acid dihydrate obtained by most beekeepers.
*Distilled water may be necessary if you have “hard” (calcium-rich) water that reacts with the OA. To test, heat up some of your tap water in a clear glass container, then stir in a tsp of OA. If the water turns (and stays) cloudy white, there is too much calcium.
**Granulated sugar can be roughly measured by volume –1 pint weighs ~1 lb; 1 qt weighs ~2 lbs.
Storage
Oxalic acid dissolved in water is relatively stable. But when sugar or glycerin is added, chemical reactions take place. Sucrose gets inverted into glucose and fructose, which may actually make the dribble better stick to the bees’ bodies. But the sugar degradation product HMF is also produced (as a function of time and temperature). If consumed in quantity, HMF can be toxic to bees, but bees don’t like to consume acidic syrup, so I don’t know whether it is an issue. But if you keep the solution refrigerated in a glass or plastic container, very little HMF is formed.
See A scientific note on long-term stability of a home-made oxalic
acid water sugar solution for controlling varroosis https://hal.archives-ouvertes.fr/hal-00891898/document
© Randy Oliver 2018