Scientific Beekeeping: Research on Oxalic Acid

Scientific Beekeeping     By Randy Oliver     February 22, 2018

 Hi All,

Thanks so much for your feedback on the mite model--I received over 700 responses, many with constructive comments that I forwarded to the class.  Voting went overwhelmingly to the original graph--596 for it; 26 for the individual graphs; 11 for both.  I suggested to the class a way to present all options--taking first-time users step-by-step, with options.

I'm heartened by the number of you worldwide who have already used the mite model.  Your feedback and notes of appreciation make my day!

I'm currently deep into cage trials to attempt to determine the optimal formula for the extended-release oxalic acid treatment.  I'm trying different ratios of OA to glycerin, as well as using the very similar food-grade solvent propylene glycol.  I'm finding that both humidity and degree of saturation of the towels can make huge differences in whether the treatment hurts the bees.

I've also figured out how to quantify the precise amount of oxalic acid on the bees' bodies using titration:

I'm able to accurately quantify the amount of OA to less than 1/10,000th of a gram!  I now know how much OA is harmful to the bees, and will soon resume testing to see how little is necessary to kill the mites.

I've recently posted three new articles:

Not surprisingly, the first is Progress Report #3 on the above topic of the extended-release oxalic treatment.

The next two are numbers 14 and 15 in my "The Varroa Problem" series.
One discusses in-hive virus dynamics and the need for early mite treatment.
The other models the expected effect of various mite treatment options, especially repeated oxalic acid vaporizations (would also apply to sugar dusting).

Here at home, our beekeeping season is well underway.  Almond bloom in California is nearing an end, just as frosty air moved in to threaten the nutlets with freezing.  We've suddenly gone from a balmy early spring, to winter conditions.  Indeed, we started grafting queen cells as it was snowing.  My sons Eric and Ian are doing a great job at taking over the operation--we went to almonds with our highest colony count yet, and graded at over 15 frames average in those orchards that got graded per contract--giving them a nice bonus!

Happy Beekeeping to All!


(Please note: Randy Oliver's research on oxalic acid is supported entirely by donations from beekeepers.)

Oxalic Acid Treatment - Trickle Method

Bee Craft B-kids

Photo: BBKAOxalic Acid Treatment - Trickle method

It is easy to forget about varroa mites at this time of year but you do so at your peril!

You can use the oxalic acid treatment only when the colony is broodless, ie. in early winter (or on a newly collected swarm). The aim of treating in winter is to reduce the varroa infestation level to an absolute minimum so that no further treatment will be necessary before late summer. Oxalic acid is an anti varroa treatment method which leaves no residues in hive products, it is a natural organic substance and effectiveness is over 90%.

It is important to make sure your colony is broodless as the acid will only kill mites on the bees, not those on larvae in the honeycomb cells. How to tell when brood rearing has finished? Brood rearing in autumn is influenced by apiary location, but more so by the weather. The British weather has been unseasonably mild lately but the first night frosts will cause the queen to stop egg laying. Three weeks later the colony will be brood free. At this time the oxalic acid trickle method is most effective.

The treatment is carried out using a warm sugar syrup solution at an oxalic acid concentration of 3.5% applied using a syringe or some other suitable device. This can be purchased ready mixed from your beekeeping equipment supplier. 5ml (no more!) of the acid mixture should be trickled onto each seam of bees in each occupied chamber (seam = the space occupied by bees between two frames). This procedure is most easily accomplished when the bees are clustering, so choose a fine, still day in December or early January when temperatures are at or around 0C. The removal of the hive roof and crown board to facilitate the treatment has no detrimental effect on the bees as long as you carry out the procedure quickly!

Before treating, remember that not every colony needs to be treated. A check on the natural mite fall about now is advised. Insert the removable floor and note the natural mite fall a week later. If the fallen mites are light coloured there is still emerging brood in the colony! If the mite fall is more than 1 mite per day treatment is recommended, more than 5 mites per day needs immediate treatment. If untreated colonies indicate an average of 1 mite per day in November, this indicates that there are still some hundreds of mites in the colony.

The treatment must be administered only once. Repeated applications are not tolerated well by the bees and are pointless anyway in a brood free colony.

NB. Oxalic acid treatment can also be applied using a vaporiser.

From Bee Carft B-kids 12/5/15 FB Post:

Is Your Hive Ready For Winter?

Is Your Hive Ready For Winter? Read & Sign up for the Brushy Mountain Bee Farm E-Newsletter:
We had a busy month in September. 

Our folks at Ruhl Bee in Oregon worked their tails off to move from Gladstone, OR to Wilsonville, OR. It is only about a 15-20 minute drive but a move is a move no matter how far. They then came east and then we went west for training an
At the end of September the Bee Informed Partnership (BIP) released the results of the 2014-2015 Management Survey. First, if you don't know who BIP is, you should! In short, it is a group funded by grants which collects data  from beekeepers to determine colony loss and what management techniques they are using.

It is important to note that correlation does not equal causation. This is a fancy way of saying that just because people lost 37.5% fewer colonies when they used Oxalic Acid as a varroa treatment compared to those that didn't use anything at all, does not mean that Oxalic Acid is the reason for the better result. 
I could write pages on their results covering varroa treatments, drone trapping, antibiotics, small cell, etc, but I think it better if I simply give you the link to the results. I strongly encourage you spend time reviewing the wealth of information as I think it can make us all better beekeepers. Further, I would encourage you to participate in the survey next time to only improve our collective beekeeping knowledge.   Here is the link.

Oxalic Acid FAQs

Brushy Mountain Bee Farm Blog  September 18, 2015

Oxalic Acid is a naturally occurring acid found in plants. It became popular in Europe & Canada for treating Varroa Mites in a honey bee hive.

IS IT A LEGAL VARROA TREATMENT IN THE UNITES STATES?Oxalic Acid has been approved by the EPA to treat honey bee colonies in the United States. It must pass state approval before it may legally be sold in each state. This is a continuing process and a list of states that have been approved can be found on our website.

Versions of Oxalic Acid can be found in hardware stores but those have various additives mixed with them that can cause issue with the bees. Also it is illegal to use them for hives.

WHEN IS THE BEST TIME TO USE OXALIC ACID TO TREAT?The most effective time to treat a hive with Oxalic Acid is when a hive has little to no sealed brood. It cannot penetrate capped brood so it will have no effect on the next generation of mites that were left in capped brood. You can treat in the spring and summer but research shows that Oxalic works best in the fall/winter.

WHEN WILL MY HIVE BEE BROODLESS?The best time for a broodless hive is during late fall through the winter. You can also manipulate the hive by caging the queen for 14 days. That keeps her from laying and capping any more brood. 14 days provides enough time to treat your hive and allow the treatment residue to subside before returning the queen to lay brood.

CAN YOU TREAT IN THE SUMMER?While some studies say you can treat honey bees in the summer, there are too many variables that can cause issues during summer treatments. Summertime is usually when the hive is full of capped brood so it could take multiple treatments to reduce all the mites concealed with the brood. Continuous multiple treatments can affect the bees severely.

CAN YOU TREAT DURING A HONEY FLOW?It has not been approved for use during a honey flow. If you have honey supers on the hive you must remove them before treating and leave them off for at least 14 days to give the Oxalic Acid treatment time to be fully cleansed from the hive to avoid contamination of the honey.

HOW CAN IT BE USED TO TREAT?There are three approved methods to treat with Oxalic Acid:
Solution Method:Note: To completely dissolve Oxalic Acid Dihydrate, use warm syrup.Dissolve 35g of Oxalic Acid Dihydrate in 1 liter of 1:1 sugar water (weight : volume). Smoke bees down from the top bars. With a syringe or an applicator, trickle 5 ml of this solution directly onto the bees in each occupied bee space in each brood box. The maximum does is 50ml per colony whether bees are in NUCs, single, or multiple brood chambers.
Under certain unfavorable conditions (e.g. weak colonies, unfavorable overwintering conditions), this application method may cause some bee mortality or overwintering bee loss.
complete kit is available with all the parts you will need for Solution Method (35 grams Oxalic Acid, nitrile gloves, protective goggles, 60mm syringe, and instructions)
Vaporizer Method:Apply only to outdoor colonies with a restricted lower hive entrance. Seal all upper hive entrances and cracks with tape to avoid escape of Oxalic Acid vapor. Smoke bees up from the bottom board. Place 1g Oxalic Acid Dihydrate powder into vaporizer. Follow the vaporizer manufacturer’s directions for use. Insert the vaporizer apparatus through the bottom entrance. Apply heat until all Oxalic Acid has sublimated.
Spraying Package Method:Ensure bees are clustered before applying.Spray broodless package with 1:1 sugar water solution (without Oxalic Acid mixed) at least 2 hours before spraying with Oxalic. This fills their stomachs to reduce ingestion of Oxalic Solution.Mix 1:1 ratio sugar water with 35 grams of Oxalic Acid (same ratio as Solution Method). For a 2 lb package, use 21mL of solution. For a 3 lb package use 31mL solution.Store bees in a cool darkened room for 72 hours before hiving.

HOW MANY HIVES CAN OXALIC ACID TREAT?*All totals calculated from dosage amounts listed in treatment methods above.Solution Method: 20 hivesVaporizer Method: 35 hivesSpraying Package Method: 47 2lb packages & 30 3lb packages

WHAT SAFETY MEASURES SHOULD I TAKE WHEN USING OXALIC ACID?DO NOT let Oxalic Acid make contact with skin, eyes, or be ingested. Wear proper personal protective equipment (rubber gloves, safety goggles, long sleeve shirt) when mixing or distributing Oxalic Acid. If exposure to skin or eyes does occur consult directions and safety sheet for instructions. If severe reaction occurs, call 911. Wash hands, exposed skin, and PPE directly after treatment to avoid contamination.

HOW EFFECTIVE IS OXALIC ACID?The effectiveness of Oxalic Acid treatment can be in excess of 95%, but solution method have a higher efficacy.

HOW MANY TIMES SHOULD I TREAT MY HIVE?You will only want to treat your hive ONCE during the fall/winter. Honey bees have a low tolerance to Oxalic Acid.  Overexposure can cause issues and death in the hive.

As with any other treatment, some bee mortality may occur, especially if hive is already weak. Check your mite count and strength of hive before applying any treatment. If you are uncertain of hive’s strength, you can get a second opinion by asking a local beekeeper or your local bee inspector.

CAN I USE OXALIC ACID WITH OTHER MEDICATIONS?Since it is a naturally occurring chemical, it can be used in conjunction with other non-varroa treatments. DO NOT mix directly with other chemicals while treating.

HOW DO YOU STORE OXALIC ACID?Dried, unmixed Oxalic Acid should be kept in a cool dry place will not expire.Mixed solution can last up to a week at room temperature and a few months if kept in the fridge.

Read at:

Webinar: Using Oxalic Acid In The Beehive

 Brushy Mountain Webinar Wednesday August 19, 2015   3:00-4:00PM

This varroa treatment has been around for years but has not been approved for use in the United States until now! With its high efficacy and low risk of contamination, many beekeepers are looking to use it this year. We have brought in an expert panelist, Randy Oliver, to better explain Oxalic Acid. If you have not had the opportunity to read his blogs, seen him speak at bee conferences, or kept updated with his articles in American Bee Journal, we hope you will take the time to listen to him discuss Oxalic Acid.

To Register:



EPA Okays Oxalic Acid for Varroa Mite Control

ABJ Extra  March 12, 2015

Registration Decision for the New Active Ingredient Oxalic Acid


This document announces the decision by the U.S. Environmental Protection Agency (EPA) to register the new active ingredient oxalic acid for use against the Varroa mite, a parasite on honeybees. EPA has concluded that oxalic acid meets the regulatory standard under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). One product is registered under Section 3( c )(5) of FIFRA, "Oxalic Acid." The application for this registration was submitted by the United States Department of Agriculture. Due to the significant problems this parasite poses for honeybees, the EPA review of the application was conducted under a greatly expedited process.


1. Application for Registration 
The Varroa mite, Varroa destructor, is a serious and devastating pest of honeybee colonies. Varroa mites are parasites that feed on developing bees (larvae and pupae; brood) leading to brood mortality and the reduction ofthe lifespan of workers that were parasitized during development. Varroa can affect hypopharyngeal gland development of nurse bees and decrease brood/royal jelly production affecting...

Read more:

Comment Now-Oxalic Acid Registration for Varroa Treatment

Pollinatory Stewardship Council   By Michele Colopy  February 28, 2015

Tennessee State Beekeepers aptly stated in their June 2006 issue of The Antennae 
( ), “It’s anybody’s guess when oxalic acid will see registration in the USA.  Most likely years, but it will happen.”

Tennessee State Beekeepers predicted it: it has been years, but the U.S. registration of oxalic acid for treating Varroa mites on honey bees is here.

Oxalic Acid has been used in the UK for about ten years; in Europe it has been used for at least 20 years.  It is highly effective; kills varroa by dessicating the mouthparts, and only affects honey bees in a very minor way.  In the UK a beekeeper stated there are three methods of applying oxalic acid:
•    Vaporization  (rarely if ever used these days - too technical, expensive and “fiddly” - hot metals and electricity involved)
•    Spraying  (rarely used - danger of breathing in spray or contaminating eyes)
•    Trickling.   This is the standard method - easy, cheap, no heat or electrics needed, no masks, no eye protection.   With trickling, you simply trickle an oxalic acid/ sugar solution into each “seam” of bees.

For a US beekeeper’s input on using oxalic acid go to Scientific Beekeeping  . . .  and  

Approval of the application for the registration of oxalic acid use would give U.S. beekeepers another tool in their fight against Varroa.  It is however, not a remedy which will be utilized by all beekeepers.  Beekeepers know what is best for their honey bees.  A reduction of Varroa mite population is the key to healthy honey bees.  The beekeeper’s voice is the most important one here: make yourself heard. 

Your comments must be received by the EPA by March 6th 

Applications for new active ingredients (Other products are part of this application for “new active ingredients:” the link to the docket is below.)!documentDetail;D=EPA-HQ-OPP-2015-0043-0001

Make the beekeeper’s voice heard.  Send your comment today.

The process is fairly simple and we have drafted a letter for you:
1.    Copy the text of the Letter Re Oxalic Acid
2.    Select the link to the Docket at (Below)

Applications for new active ingredients (Other products are part of this application for “new active ingredients:” the link to the docket is below.)!documentDetail;D=EPA-HQ-OPP-2015-0043-0001

3.    Select the COMMENT NOW button on the right side of your screen   
4.    Paste the letter into the Comment box
5.    Add your own comments
6.    and follow the prompts to submit your comments at
7.    your comment will appear within 24 hours in the docket.  

Thank you!

Oxalic Acid Registration Comments Wanted by EPA

BEE CULTURE: CATCH THE BUZZ         February 5, 2015

 By Alan Harman

   There’s great news for beekeepers with the U.S. Department of Agriculture seeking approval for the in-hive use of oxalic acid dihydrate to control Varroa mites.
   It’s a treatment long used in Europe that kills up to 97% of mites in a hive,
   The government’s Federal Register lists an application for Environmental Protection Agency approval for the product, long successfully used in Europe in the colony against Varroa.
   The notice is signed by Robert NcNally, director of the Biopesticides and Pollution Prevention Division of the Office of Pesticide Programs.
    A spokeswoman at the EPA’s Office of Pesticide Programs confirmed receipt of the USDA application.
   Approval of the application would give U.S. beekeepers a new weapon in their fight against Varroa.
  European beekeepers say they successfully use vaporized oxalic acid, or a 3.2% solution of oxalic acid in sugar syrup, as a miticide against Varroa.
   It can be used in both the liquid form and as crystals that can be evaporated by electric heater pans.
   Oxalic acid had been successfully used by beekeepers in the United Kingdom for several decades to kill Varroa when Sussex University conducted a study to determine the effectiveness of different doses and application methods of oxalic acid on mite and bee mortality.
   The experiment involved 110 hives comparing three application methods and three different doses that was completed in 2014. Hives were treated in early January 2013 when they had no brood.
   Oxalic acid does not kill Varroa in sealed cells, but rather kills mites carried on the bodies of workers and also those crawling in cells not yet capped.
   The researchers determined the proportion of mites killed by washing the mites off a sample of about 300 workers bees immediately before and after 10 days of treatment with oxalic acid.
   They also determined the number of bees killed at the time of treatment, together with hive mortality and strength four months later in spring.
   The university says the results came to a clear and encouraging conclusion. Application of oxalic acid via sublimation, where it is applied in its pure form by vaporizing the crystals with a special heated tool, was superior to application as a solution via either spraying or dribbling.
   Sublimation gave a greater kill of Varroa at a lower oxalic acid level and showed no increase in bee mortality. In fact, four months after treatment, the hives treated via the sublimation had more brood than the 10 untreated colonies.
   The sublimation method is quick and easy, as the hives do not need to be opened.
   To confirm the results, the sublimation technique was retested a year later in broodless honey bee colonies.
   “An amazing 97% of the Varroa were killed by using 2.25 grams of oxalic acid per hive, and colony survival three months later in spring was close to 100%,” the university says.
   It says beekeepers only need to carry out this treatment once a year because it reduced the number of mites so dramatically it takes them a long time to build back up again.
   The Federal Register notice says the application potentially affects those involved in crop and animal production, food manufacturing and pesticide production.
   Comments must be received by the EPA on or before March 6.
   Oxalic acid dihydrate is a colorless, odorless, crystalline solid. It is potentially fatal if swallowed or inhaled. It can also cause discoloration, irritation and burns of the skin as well as permanent damage to the eyes.
   One operating manual says all employees who handle this material should be trained to handle it safely.
   “Areas in which this compound is used should be wiped down periodically so that this substance is not allowed to accumulate,” it says.
    In Canada, the British Columbia Ministry of Agriculture says oxalic acid dihydrate should only be applied in late fall when the colony has no brood. Any open brood in the colony is likely to be killed by oxalic acid.
   “Even though the product is not as volatile as formic acid, always wear rubber gloves and safety glasses when handling the product,” it says “Avoid inhalation of vapors.”
   The ministry says it should be applied only once.
   “Oxalic acid can be applied at cool temperatures, either through vaporization (crystals heated and converted directly into a gas vapor) or trickling an acid-sugar syrup solution onto the bees.
   One European expert goes even further.
   “It cannot be stressed too strongly that oxalic acid is an aggressive substance and needs to be treated with respect,” he says. “Acid resistant gloves and goggles should be worn and an apron of the type used by mortuary attendants, along with wellington boots that have the tops covered by gaiters so that any falling liquid cannot fall into the boot.
   “A respirator that has specialized organic acid filtering will be required in cases where the acid is sprayed or vaporized.”
   The EPA is also seeking comment on an application from Certis USA L.L.C. to market a product called BmJ WG with a fungicide that claims to reduce plant viral infections and Bacillus mycoides isolate. It is intended for use on almonds, citrus, cole crops, cucurbits, fruiting vegetables, grapes, legumes, lettuce, pecans, pome fruits, potatoes, spinach, and sugar.

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