“Using Liquid Formic Acid for Mite Control”
Bee Culture (June 2003), Vol. 131 (6): 17-19


Dr. Malcolm T. Sanford


In the April 2003 edition of Bee Culture, Editor Kim Flottum says he fails to understand the situation surrounding the use of liquid formic acid for mite control.  Although beekeepers do many things that are potentially dangerous to their health, Mr. Flottum says, the use of a somewhat benign substance, like formic acid, seems to be singled out by regulators as a special case.  One of the reasons for this is that no specific label exists, the standard that regulatory officials use when determining pesticide use.  According to pesticide regulations, now found as Title 7 of the U.S. Code, any chemical that is intended to control pests is by default a pesticide.  According to Mr. Bill Ruzicka, “Using formic acid is similar to using Borax or Baking Soda to kill ants; neither is registered as a pesticide. It is your right and your decision to use acid. Advising someone else to use an unregistered pesticide is illegal on US soil.”1   Meanwhile he says that unless the American beekeeping federation, or some other entity registers the generic use of liquid formic acid, the U.S. beekeeper will in all probability never see its registration.

The "soft chemical" formic acid is presently used in several countries in Europe2 as well as Canada3 and New Zealand,4 in the continuing struggle to control mites in honey bee colonies.  Formic acid appears to be a good candidate because it is a relatively small compound with a molecular weight of  46.03, which may be responsible for reports that it can penetrate brood cappings and kill mites sealed in the cell (Mr. Ruzicka says it actually must be brushed on the cappings to be effective).  It is also found naturally in many, but not all, honey types.  Finally, formic acid is known to control populations of both the internal tracheal mite (Acarapis woodi) and the external, exotic Asian mite, Varroa destructor.  Most chemicals currently in use are effective against only one or the other of these honey bee parasites and cannot kill mites that are protected inside capped brood cells.

Several reasons exist for lack of a liquid formic acid label, including the fact that no commercial entity is expected to undertake the extensive testing necessary to bring the material to market.  The liquid cannot be patented and is already manufactured and available for a number of uses.5  Therefore, exclusively manufacturing and/or marketing it strictly for a beekeeping use has limited commercial appeal.  Formulations that incorporate the liquid into self-delivery devices are in the regulatory pipeline in the United States and could be approved in the future.  These are considered superior to the liquid acid because they would be easier and safer to handle, but their manufacture has been plagued with problems and they are sure to be more expensive than using the liquid itself. 

Formic acid is employed as a fumigant and, therefore, must reach all bees in the vapor state.  In addition, because it affects tracheal mites as well, molecules must also be delivered inside the bee's tracheal (breathing) system.  Delivery of chemicals through fumigation to honey bee hives is much less reliable than molecules delivered on plastic strips.  A reason for this is that the liquid must first be evaporated (a temperature-dependent process) before it becomes effective.  The ideal ambient temperature for delivery of liquid formic acid is between 60°F (16°C) and 80F (27 °C).  Since honey bees actively regulate the temperature of their hive, this presents a complicating variable.  Release of the material through vaporization is also much less reliable with reference to dosage than using plastic strips.  It is easy to make mistakes.  Finally, for full effectiveness, formic acid treatment must often be repeated several times at fairly short intervals, whereas most of the hard chemicals can be applied less frequently.

Another reason for a lack of interest in labeling liquid formic acid is that it cannot compete with the so-called "hard chemicals" presently labeled for controlling mite populations.  Both the synthetic pyrethroids, fluvalinate (Apistan®) and flumethrin (Bayvarol®), and the organophospate coumaphos (CheckMite®) are reported to eliminate in excess of 90 percent of Varroa mites, the most damaging organism in colonies, whereas formic acid only kills around 70 percent.  The same is true for the chemical amitraz, a triazapentadiene, which controls both Varroa and tracheal mites, but has no label in the United States (marketed as Miticure® for a short while before being abandoned) although in Europe it is marketed as Apivar®.  These hard chemicals are also easier to apply.  They are formulated on plastic strips and kill by contact; the molecules are distributed by bees’ contacting the strips.  An important consideration is that if liquid formic acid is labeled, there is a risk that these other hard chemical controls now labeled and legal might no longer be supported, and could easily be pulled from the market by regulators, making them no longer be available to beekeepers. 

A closer examination of the situation reveals that the relative advantage that hard chemicals now have is becoming less with time.  After ten years of pyrethroid use (Apistan®) and Bayvarol®), Varroa mites continue to become resistant to this class of chemicals in most parts of the world.  More worrisome is that for the relative new organophosphate, coumaphos (CheckMite+®), the time to reach resistence is much shorter (three to five years).  And it is not certain whether rotation of these materials, the classic resistance management strategy in agriculture to conserve lethality, will be effective.  An alternative hard chemical class to those pesticides already in use is not known at the present time.  If one is found, the likelihood that it would be approved is small, and at the very least the application process to become a labeled product would consume a great deal of time and money.

Although pyrethroids are considered fairly benign to mammalian systems, there is concern that these materials accumulate in wax.  In addition, there is evidence that long-term fluvalinate use has sublethal effects on honey bee colonies that can affect productivity.  Far more problematic is the organophosphate called coumaphos.  Many believe the premature failure (supersedure) of many commercial queens in the United States can be blamed on contamination of the nest with this material.

The U.S. Environmental Protection Agency (EPA) has targeted the organophosphate class of pesticides to be eliminated in the near future under the Food Quality Protection Act (FQPA).6  Chemicals in this class are potent nerve poisons and their long-term use is considered a risk not only for the applicator community, but the food consumer as well.  Fortunately, both fluvalinate and coumaphos have allowable residues in honey and wax, which are not exceeded when using the materials according to the label.  Both, however, also have the capacity to bioaccumulate in wax over time, setting the stage for contamination of beeswax, which is routinely recycled in beekeeping operations.  An increasing amount of beeswax is already suspect, and no longer considered suitable either for cosmetic use or to give back to the bees as foundation to produce more comb.  Honey is considered somewhat safe from residues in that the active ingredients are soluble in fats, not water. 

Residues and risks, however, are not confined to the above labeled formulations.   Unfortunately,  there is a large body of anecdotal evidence that many beekeepers are using the active ingredients fluvalinate, amitraz and coumaphos in unregistered and illegal formulations in spite of information that this activity can result in the long-run in unacceptable residues, a "smoking gun" for regulators and consumers (the press).  A sign of this is that Varroa mites in the United States have become resistant to amitraz, a material that except for a very short time, has had no label. Should substantial amounts of these chemicals be found in honey, there exists the real possibility they will be lost to beekeeping use.

A recent example of the risks beekeepers run by using unlabeled materials is rejection at ports of entry of large amounts of Chinese honey contaminated with the antibiotic chloramphenicol. This was first discovered in the United Kingdom and then the Canadian Food Inspection Agency (CFIA).  This produced a regulatory furor, and also was in part responsible for a worldwide shortage of honey, causing a price spike.

Residues can be a problem for any chemical introduced into a beehive.  Formic acid, however, is found naturally occurring in many (though not all) honey.  Because it is a simple molecule, it also will not bioaccumulate permanently in wax and honey.  Over time, it is expected to diffuse out of these materials, rather than be chemically bound up as are many hard chemicals.  Formic acid is also exempted from the requirement of a tolerance in honey and beeswax by federal regulators.7  All these characteristics make the use of liquid formic acid favorable to certify "organic" honey production.  Whether mites can become resistant to formic acid treatment is not clear.  Technically this is feasible, but so far where the acid has been used for a number or years this does not seem to be a concern. 

As noted above, there is considerable risk involved in handling liquid formic acid for both honey bee and beekeeper alike.8  It is not a material to take lightly, but experience shows that it can be applied safely by taking appropriate precautions.

Most research on formic acid has been accomplished in temperate climates, where the material has been found to be relatively effective.  A great deal of experimentation is needed to determine its effectiveness in subtropical and tropical climates.  In the final analysis, the application parameters must be developed by each beekeeper using the material under local, specific conditions. Queen and worker bee losses are common when the material is not applied correctly.9  Effective application, therefore, requires a different mind set than use of previous materials, where a label gives detailed and legal instructions for use in many environments.  This also could make formal labeling of formic acid in the U.S. much more complex.

The use of liquid formic acid can be looked at as a way to transfer application “risk” from the consuming public to the beekeeper.  The tradeoff is that beekeepers will be much more at risk of harming both themselves and their bees with inappropriate application, while potential product contamination , putting consumers at risk, is minimized.  Liquid formic acid can be easily and legally purchased in several concentrations; 85 percent is most common.  A concentration of 60 to 65 percent is generally recommended for beekeeping use and so it will often be necessary for users to acquire sufficient education and experience to dilute the material to the proper level. 

A number of devices have been developed to vaporize liquid formic acid in bee colonies.10  The Nassenheider Evaporator, available commercially, has received a lot of exposure.11  Do-it-yourself evaporators can also be made.12


In the Americas, the Canadians have developed some effective devices.  The Ontario Beekeepers Association has produced a system using a material called Homsote (Tentest Board) in Ziplock® plastic bags.13  Mr. Bill Ruzicka has also developed a product using specific evaporator pads.  His MiteGone® system is "astonishingly simple," and the cost is very low.  He is looking for cooperators and already has an international list of associates published on his World Wide Web site, which also distributes educational materials in various formats.14 


The Canadian beekeeper Allen Dick on his instructive World Wide Web site discusses in great detail his experiences with formic acid.15  He concludes:  "This article is an attempt to bring information forward without any judgment of the claims of the originators. One of its strongest points is the lack of harmful residues in honey and wax.  Its major drawback is that treating with formic involves handling of a dangerous substance."  On the horizon, Mr. Dick also sees another natural substance, oxalic acid, as a strong possibility in the future of mite control in honey bee colonies.16




1.  Mitegone World Wide Web site, accessed April 18, 2003 <http://www.mitegone.com/forms/Legality%20of%20Acid%20and%20Availability.pdf>


2.  Apiservices Mega World Wide Web site, accessed April 11, 2003< <http://www.beekeeping.com/articles/us/formic_acid.htm >


3. Allen Dick's World Wide Web Site, accessed April 11, 2003 <http://www.internode.net/honeybee/Formic/cdnformiclbl.htm >

4. New Zealand Beekeepers Association World Wide Web Page, accessed April 11, 2003 <http://www.nba.org.nz/varroa/Formic-acid-guideline.PDF>

5.  Louisiana State University World Wide Web Page, accessed  April 11, 2003 <http://www.camd.lsu.edu/msds/f/formic_acid.htm >

6.  Food Quality Protection Act implementation World Wide Web Page, accessed April 11, 2003 <http://www.ecologic-ipm.com/menu.html >

7.  Environmental Protection Agency Web Page, accessed April 11, 2003 <http://www.epa.gov/fedrgstr/EPA-PEST/1997/February/Day-05/p2712.htm

8.  Occupational and Safety Hazard Agency World Wide Web Page, accessed  April 11, 2003 <http://www.osha-slc.gov/SLTC/healthguidelines/formicacid/recognition.html >

9.  Canadian Honey Council World Wide Web Page, accessed April 11, 2003 <http://www.honeycouncil.ca/currie02.html>

10. Swienty Corporation World Wide Web Page, accessed April 11, 2003 <http://www.swienty.com/engelsk/varroa.html>

11.  Dave Cushman's World Wide Web Page, accessed April 11, 2003 <http://website.lineone.net/~dave.cushman/nassentest.html >

12.  Dave Cushman's World Wide Web Page, accessed April 11, 2003 <http://website.lineone.net/~dave.cushman/beesyevap.html>

13.  Allen Dick's World Wide Web Page, accessed April 11, 2003  <http://www.internode.net/honeybee/Formic/slowformic.htm>

14.  Mitegone World Wide Web Page, accessed April 11, 2003 <http://www.mitegone.com>

15.  Allen Dick's World Wide Web Page, accessed April 11, 2003 <http://www.honeybeeworld.com/formic/default.htm>

16.  Allen Dick's World Wide Web Page, accessed April 11, 2003 <http://www.honeybeeworld.com/formic/default.htm#Oxalic Acid>