Varroa mites can weaken your colony and make your hive susceptible to secondary pests. Oxalic acid is one of the best ways to manage your varroa populations in your hive. Oxalic acid kills 90-99% of the phoretic mites in your beehive. To reach these levels of effectiveness, however, the colony must be broodless. Your beehive is naturally broodless in the winter, but it is also broodless when you pick up your three-pound package of bees. Treating package bees with oxalic acid can be useful to ensure that you’re setting up your bees for a strong pest-free start.
Do package bees have enough mites to treat with oxalic acid?
Some might justifiably argue that treating package bees whose mite load is unknown is overkill. Much like we don’t want to create antibiotic-resistant bacteria by overusing or incorrectly using antibiotics, we don’t want to create a super varroa mite either. After all, they are deadly enough as they are. Package bees, however, arrive at your home with varroa. According to one study, package bees contain a wide range of varroa levels, from .4 go 5.4 mites per 100 bees (Cited in Aliano).
When a colony is broodless, an acceptable population of varroa in a hive is generally considered to be about 1%, or 3 mites per 100 bees. Anything beyond that number may necessitate treatment. Moreover, mite populations can double each month in colonies with brood (Honey Bee Health Coalition). This means that it would not be unusual for you to receive a package of bees with a sufficient mite load to merit treating with oxalic acid.
Of course, you could test your population of mites on bees prior to treating. Using the sugar-roll or alcohol-wash method would inform you of the mite load. However, I personally wouldn’t want to use the alcohol-wash method as it kills 300 bees, and I want every bee possible working to make my package of bees a successful and flourishing hive.
How to treat package bees with oxalic acid
As of 2015, the EPA has approved these methods for treating package bees with oxalic acid.
- The bees must be in a cluster. This means that you should store the bees in a cool dark place before applying the solution. The directions for using oxalic acid suggest storing the bees in that cool, dark place for 24 hours to create the cluster.
- As Aliano and Ellis did in parts of their study, you can create an artificial cluster if the weather is warm. Briefly chill your bees for 20 minutes in 35 degree temperature, which is just about the temperature of your fridge.
- Spray your bees with a 1:1 sugar syrup two hours before spraying with oxalic acid. This ensures that your bees are well-fed before you spray them with the oxalic acid solution.
- Create a 2.8% oxalic acid solution by dissolving 35g of Oxalic Acid Dihydrate in a liter of 1:1 sugar syrup.
- Spray 3.0 mL of the 2.8% oxalic acid solution per 1,000 bees in the package. A two-pound package of bees typically has about 7,000 bees (requiring 21 mL or 3.5 teaspoons). A three-pound package of bees has about 10,000-12,000 (requiring 31 mL or 5 teaspoons).
- Make sure to spray the bees evenly on both sides of the package.
- Store the bees in a cool, dark place for 72 hours before installing your package in the hive.
It’s also important to note that you should not use oxalic acid on your bees more than twice a year. If you treat your package, you may treat your hive again for the winter broodless period when it will again be most effective. If your hive has a high load of mites during the summer, you will want to consider an alternate form of mite control.
Disadvantages of treating package bees with oxalic acid
From my perspective, the disadvantage of using oxalic acid on a package of bees is the time and temperature requirements. I want to get my bees in the hive and start giving them sugar syrup so they can hit the ground running (or air buzzing, in the case of bees). Delaying an additional three to four days while the spring nectar flow is starting seems like an abysmal waste of opportune foraging.
In addition, you must carefully monitor your package during those 72 hours to ensure that the bees have sufficient food. The sugar syrup in their package and that the sugar syrup can is still full and accessible, i.e., that it hasn’t become blocked in some way. The last thing you want to do is treat your bees for varroa and then accidentally starve them.
As a beekeeper in Kansas, moreover, the weather is rarely obliging and can vary dramatically day to day, especially in spring. If you keep the bees somewhere too warm, they will die during that time period. I do not have a basement, and the garage is only an option when the weather is sufficiently cool. You must have obliging weather or a good place to store the bees.
After the stress of the journey to arrive at my house in a three-pound package, a further delay seems detrimental to their health. At the same time, few things seem more detrimental to health than varroa mites. Ultimately, as the beekeeper, you make the call with the information you have at your disposal.
Aliano, Nicholas P. and Marion D. Ellis. “Oxalic Acid: A Prospective Tool for Reducing Varroa Mite Populations in Package Bees.” Experimental and Applied Acarology, 48 (2009), pp. 303–309. Accessed 12 April 2018.
Berry, Jennifer. “Oxalic Acid: Effective & Easy on Bees, But…” 25 May 2015. Bee Culture. Accessed 12 April 2018.
Honey Bee Health Coalition. “Tools for Varroa Management: A Guide to Effective Varroa Sampling and Control.” Honey Bee Health Coalition, 6th Ed. 7 April 2017. Accessed 12 April 2018.
United States, Environmental Protection Agency, Office of Chemical Safety and Pollution Prevention. Oxalic Acid Dihydrate. 2015. Accessed 12 April 2018.