A Blog post by Jim Stellern summarizing Jennifer Berry’s Advanced Beekeeping Workshop presentation “Oxalic Acid Research:  Three Years in the Making”

On the first night of the Three Rivers Beekeepers’ 2021 Advanced Beekeeping Workshop, Jennifer Berry provided an excellent summary of the results from her research projects involving oxalic acid treatment for varroa mite control and provided a great overview of varroa and oxalic acid in general.

Jennifer Berry has been the Apicultural Research Professional and Lab Manager for the University of Georgia Honey Bee Program for over 20 years. Her research has focused on queen breeding, improving honey bee health, Integrated Pest Management techniques for Varroa and small hive beetle control, sub-lethal effects of pesticides on beneficial insects, weeds for bees, and what best to plant in non-traditional landscapes to enhance pollinator populations and diversity. (https://bees.caes.uga.edu/about-us/jennifer-a–berry.html)

Here is a brief summary of some of the points Jennifer made:

Varroa mites can reproduce in worker brood at least 1.5 times and up to 5 times in drone brood.  So in the spring when there is more drone brood, mites can reproduce more rapidly.  Varroa infect bee larva with viruses while the larva is developing under the brood capping.

Mite populations ramp up through the spring as more bee brood is available.  In late summer the mite population can exceed the bee population as the queen shows down brood production.

Jennifer cautioned against following what you see on the internet unless it has been tested and verified for effectiveness using a rigorous process.  Her research is done in multiple locations with at least 10 hives per location and groups of control hives.

Jennifer collaborated with Randy Oliver to recreate his test of the effectiveness of using shop towels soaked in oxalic acid and whether this slow-release approach to killing varroa would work in the hot humid climate of Georgia (similar to Missouri climate).  Her tests showed using shop towels soaked in oxalic acid was no more effective than a control group (which received no treatment) at reducing varroa levels in hives.

In separate research, Jennifer treated hives 7 times (5 days between treatments) with oxalic acid during the summer (Sept-October in GA) and the results showed no impact on bringing down mite counts vs a control group of hives which were not treated at all.  This is a significant finding given this approach is often promoted as an effective summer treatment when brood is present.

Jennifer had the following recommendations for effective treatments with Oxalic acid:

Treat your hives in the winter during a broodless period when temperatures are between 35 degrees and 55 degrees. You can use either the dribble method or the vaporization method (see separate blog on Three Rivers Beekeepers website for more information on these methods).

Treat your hives in the summer with oxalic acid by creating an artificial brood break. Start on day 1 by isolating your queen for 14 days. There are several ways to do this. Jennifer suggested moving the queen above a queen excluder into an upper box which has only one frame for her to lay eggs and the other frames are either undrawn or full of honey. You want to control and limit the number of frames the queen can lay eggs in. You will leave her in the upper box for 14 days, then remove the queen excluder which frees the queen. After you remove the queen excluder, check and remove any queen cells from the bottom brood box. Also remove the frame the queen had access to lay eggs into, and either sacrifice or if multiple colonies are being treated, make additional splits. Then 7 days later (day 21), vaporize the hive with oxalic acid. By day 21, there should be no capped brood in the hive therefore no varroa under the wax capped brood. The oxalic acid treatment should be done early in the morning or late in the day when the majority of foragers are within the hive.

For those of you using Mel Disselkoen’s OTS (On The Spot) queen rearing process, you can incorporate an oxalic acid treatment during the broodless period following removal of the queen.   An advantage with OTS is that your time period to perform the oxalic acid treatment is several days vs just one day (day 21) as outlined in the prior paragraph.

In summary, Jennifer recommends treating hives twice a year with oxalic acid.  Once during a naturally broodless time period during winter, and once during a forced brood break in the summer.

You can also treat packages with oxalic acid after installation but before any capped brood is present.

A question was asked about how long a varroa mite can live if there is no capped brood for reproduction and Jennifer responded that Varroa can live on bees for months.  For example, a phoretic mite can live on a bee from fall, all through winter, and into spring when there would be capped brood again.

Jennifer recommended if a single hive in your apiary has a mite count that exceeds the threshold for treating, you should view your apiary as a superorganism and treat all hives in your apiary for mites to avoid varroa migration to other hives.

When using the oxalic acid vaporization method, Jennifer suggested waiting 24 hours before doing a mite count and ALWAYS wear an appropriate organic acid vapor respirator!!!!

Jennifer listed what does not work for varroa:

  • Hands off approach
  • Good riddance to bad genes (unless a comprehensive breeder program!)
  • Small cell/natural cell
  • Top bar hive/Warre hive
  • Powdered sugar
  • Food grade mineral oil, Sucrocide, Coumaphos, Fluvalinate

Jennifer listed the following ways to reduce varroa mite loads:

  • Purchase/select for tolerant queens selected for varroa tolerance
  • Splits (e.g. brood cycle disruption)
  • Drone brood trappings in early spring
  • Bottom screens
  • Less dense apiaries
  • Distance between colonies to discourage drift
  • BUT if does not work treat in spring and fall with a thymol-based product or summer and winter with oxalic acid

Jennifer offered the following ideas to keep your bees alive:

  • Purchase reputable bees/queens
  • Purchase new equipment or equipment you trust
  • Location, Location, Location!!!
    • Facing southeast, full sun, perennial water source, wind break, high spot, don’t place with heavy agricultural area
  • Keep notes on each hive
  • Take your losses in the fall
  • Regular hive assessments for queen production, disease, honey/pollen amounts, overall health
  • Don’t take too much honey
  • Must keep Varroa populations down
  • If food stores are low, feed cane sugar syrup especially during critical months, January/February and September/October


Posted 1/14/2021