The "Flash" Application Method for Formic Acid

by Jean-Pierre Chapleau

November 2003
revised February 2010

Between Fall 2002 and Spring 2003, Quebec’s beekeepers witnessed a carnage in their apiaries. Varroa was discovered as developing a resistance to fluvalinate (Apistan). 50% of the colonies in the province were lost. Many surviving colonies were weak and highly infested. What to do? A lot of beekeepers saw formic acid as the best alternative.

Formic Acid: Cure or Killer? Formic acid is known to be efficient against varroa. But how should it best be used? Presently in Canada, slow diffusion methods are the standard. The formic is impregnated in different support materials and then slowly released. Two commercial products are commonly used :
  • "Mite Wipe" a small pad containing 35 ml of acid, which will usually evaporate within 4 days;
  • "Mite Away" containing a super dose of 250 ml, which is released over weeks.
Mite Wipe needs repeated applications - up to 6 times every 4 to 7 days - depending on the level of infestation. Not quite the popular choice for a busy beekeeper ! So it was no surprise when, last Spring, most of them chose Mite Away. This situation gave rise to numerous problems.

The secret to an efficient and secure use of formic acid lies in adjusting dosage to colony population, hive size, and also to temperature conditions.

Last Spring experience with Mite Away revealed the product was not well adapted to weak colonies. In fact, damages were inversely proportional to the strength of the colonies. What’s more, the use of formic acid is not recommended in temperatures exceeding 26o C. Who is to say there won’t be a hot spell during a treatment spreading over weeks? This is precisely what happened last Spring when most regions of Quebec were hit with 30o C. temperatures exactly during the treatment period. Consequently, there were numerous losses of queens, brood and even entire colonies! Therefore, my conclusion is Mite Away does not offer the versatility required for a safe use of formic.

"Flash" application of formic from the bottom of the hive
In Europe, formic acid is given, not only by slow diffusion methods, but often as rapid volatilisation. Let us call it : "flash" treatment. In the early stages of the Varroa infestation in Canada, Kerry Clark, a former researcher from British Columbia, tested and proposed the flash method. But with the arrival of Mite Wipe and then Mite Away, it was put aside.

During a flash treatment, the acid concentration in the hive reaches a high level which rapidly decreases after 6 hours. Such a level is even said to kill some of mites in the brood. Usually the treatment is applied as follows : A dose of formic acid is poured on a piece of paper towel which has been placed either on the top bars or on the bottom board.

In our view, the flash treatment is interesting because it does permit choosing the appropriate dosage for the situation. Being of such a short duration, a flash treatment can be applied exactly when the right temperature conditions prevail. So no more bad surprises with temperature!

However, another aspect seemed very interesting to me: the possibility of not having to repeatedly open each hive by doing the application from the sampling drawer of our specifically designed integrated pest management bottom board (APINOVAR). Each of our hives rests on a screened bottom board equipped with a sampling drawer opening from the side. Slide the drawer half way open, throw in a paper towel, inject a dose of acid using a drench gun (1), slide the drawer back in! And there you have it!

I was using Mite Wipe before. These pads work well but the method is time consuming. Opening and closing the hive many times implies the wax on the inner covers and on the top bars has to be scraped out in order to maintain a good seal, otherwise the formic vapours would escape the hive from the top. Obviously the flash application from the bottom would save tremendous time and effort.

We decided to run several trials. We tested flash both as a mid-season treatment and as a fall treatment. A mid-season treatment can be needed when August mite fall reaches dangerous levels. Treating colonies during the summer requires first removing the honey supers. The problem is that all the known treatments besides flash require several days, if not several weeks. Who can afford loosing production?

Does the flash method stand up to the expectations?

As a mid-season treatment
As a mid-season treatment, the flash application gave a 60% reduction of the natural daily mites fall. Meanwhile, the control group showed a 55% increase (2). All the colonies were doubles. They received one single 40 ml dose of 65% formic. The application was made at 20o C. This level of efficiency could be obtained because the flash method effectively killed some varroas in the brood. We found some dead varroas in brood cells we uncapped during the week following the treatment. A careful examination of all the colonies showed no queen or brood damage. A higher mites fall reduction (85-90%) was obtained with another trial with a higher dosage (55 ml) at similar temperature. Nevertheless this dosage is not recommended since 4 queens out of 30 were killed and brood was damaged. A third trial with 55 ml at 13o C. revealed completely safe for queens and brood.

60% reduction is sufficient for a mid-season treatment since the objective is not to completely clean out the colony but rather permit it to safely reach the Fall treatment period. Because of the short duration of the treatment the test colonies were withdrawn from production for only 24 hours : Supers were removed during the day (normal crop removal); the colonies were” flashed” at the end of the same day and new empty supers were put back the next afternoon (3).


As a fall treatment
Flash was compared to several other Fall treatments. The trial involved altogether 225 colonies in 4 groups:

Group 1: Flash (4 applications of 40 ml)
Group 2: Thymol only (4)
Group 3: 3 applications of 2 Mite Wipe plus one flash (40 ml) (5)
Group 4: 2 applications of 2 Mite Wipe plus one flash (40 ml) (5)

Almost all colonies were doubles. All were treated during the same period (Sept 16 - Oct 12). For all treatments involving formic acid, a 65% acid concentration was used, even if the Swiss Beekeeping Research Center recommends 85% when applications are administered from the bottom of the hive. The temperatures ranged from 15o C. to 24o C. when the formic treatments were applied. Formic acid treatments were applied at intervals of 4 to 7 days, except for the last flash when it was decided to wait for good weather and more importantly for more of the last brood to be hatched. Nevertheless, there was still some brood in the colonies when the last flash application was done (6).

The flash group (group 1) had the best performance with a 92% reduction of the natural mortality). The results of this group also showed the smallest variations of efficiency. Only 14 colonies could be checked for their queen and brood. They were all ok.

The thymol group had a lower efficiency. The natural mortality reduction was only 70%. We feel that Thymol under our conditions, should not be used as a Fall treatment unless the natural mite fall is low. Even then a thymol treatment would be best followed by an application of formic acid or eventually oxalic acid.

Group 3 (3 Mite Wipe and one flash) had an efficiency almost as good as the flash group but with more variations between colonies. The average reduction has been 90%.

Group 4 (2 Mite Wipe and one flash) had the lowest efficiency: 66% reduction of the natural mortality.

It is important to mention that the goal of these Fall trials was not to rate the absolute effectiveness of these treatment options but rather to compare flash to several other treatment options in the same conditions.

Flash was also experimented on singles as a Fall treatment. The efficiency was higher. With only 3 applications we obtained a 96% reduction of the natural mites fall. This can probably be explained by the fact that colonies in singles stop feeding brood earlier. There was no more brood when the last flash treatment application was done in mid-October. As a matter of fact, for this reason, varroa control is much easier with colonies in singles.

In 2004 a standard Coumaphos® treatments was compared to 4 flash applications. Half of the colonies in each group were singles, half were doubles. The table and graph below show the results that were obtained:

2004 comparison of flash(4) with Coumaphos®:

All the queens were checked in the Flash group at the end of the treatment. All were ok.

Dosage-temperature combinations we used:
These charts summarize the different dosage-temperature combinations that we used each year. In 2004 the flash was experimented with success at higher temperatures. All these combinations were found to be safe.


   singles   doubles 
 20° Celsius   20 ml   40 ml 
 13° Celsius   27 ml   55 ml 


   singles   doubles 
 20-26° Celsius  20 ml  40 ml 
 16-19° Celsius 22 ml 45 ml  
 10-15° Celsius   27 ml   55 ml 

A test with with 50 ml at 22-24o C. on doubles in August resulted in some queens stopping laying for several days (>5%). Another queen had disappeared.

The configuration and size of our IPM board entrance differ from a standard bottom board (7). This may influence the distribution and retention of the formic vapours in the hive. We have not checked if the same efficiency is obtained with other types of bottom board with these combinations of dosage and temperature.

The following table summarizes all the trials involving flash that we conducted in 2003.

date dosages and concentration conditions number of colonies natural mite fall before natural mite fall 14 days after reduction observations
Aug. 8 55 ml doubles
27 ml singles
(once or twice at 7 days interval)
20°C end of day 21 colonies 119 (1 treatment group)

148 (2 treatments group)
10 (1 treatment group))

22 (2 treatments group)
85% (1 treatment)

91% (2 treatments)
4 queens lost for 30 applications; some brood killed; interruption in egg laying;

Aug. 15 40 ml doubles
20 ml singles
200°C end of the day 10 flash plus 14 untreated controls 116 (flash group)

52 (control group)
48 (flash group)
71 (control group)
59% reduction for flash group and a 55% increase for the control group no queen loss; no significant brood damage; no interruption in egg laying
Sept. 10 50 ml doubles
25 ml singles
around 13°C 21 colonies not available not available not available no queen loss, no brood damage, no interruption in egg laying (21 colonies inspected)
Sept. 16 to Oct. 12 40 ml doubles
20 ml singles
during the day (4 successive treatments)
65 strong colonies almost all doubles 70 6 92% reduction of mites fall 14 colonies inspected after first application : no queen loss, no brood damage
Oct. 3 50 ml doubles
variations during the day : (10 to 2°C)
2 colonies not available not available 60% of varroas on adult bees killed after a Coumaphos® check (57% et 63%) queens OK and brood OK
Sept. 24 to Oct. 12 20 ml singles 15 to 20°C 29 colonies in singles 53 2 96% reduction of mites fall queens not checked

Conclusion and discussion
In our trials the flash method showed interesting potential as a Fall treatment in replacement of chemical treatments.

In 2003, given the very high level of infestation at the outset of the treatment period, none of the alternatives tested reduced the natural mites fall to a save level for the Winter (9) but the flash method, with 4 applications, gave the best results. In 2004 the the mites fall reduction by the flash method has been more important, reaching 96,2% compared to 98% for the Coumaphos®. Theoretically with average daily natural mortality levels that would be around 25 before the treatment, a 96% reduction would result in a natural mortality under 1 varroa/day after 4 applications.

Flash also seems to be a good mid-season treatment because of both its extremely short duration and good efficiency as a single application. A mid-season flash application can release the treatment pressure in September and the number of treatments required. It is a useful tool in a IPM strategy.

The flash proved to be the fastest treatment to apply. I takes 10-15 minutes for a person alone to treat a 28 hives yard. It was also very economical. It cost approximately 0.32$ per colony for a full Fall treatment.

Flash treatment method is a versatile and economical approach. Considering our results so far, we are already planning to use it from now on as our main method of treatment for the end of the season. 2003 was the first year we did not use Apistan. I felt reassured by these results. I am now convinced that non chemical IPM is not only possible, it is also easy.

Flash would need to be tested in a wider range of circumstances and further trials are necessary to further optimize the dosages we have used.

Flash should also be experimented during Spring. We found that small or medium size colonies are affected in their development when they are continuously exposed to formic vapours for a long period. We suspect this side effect could probably be avoided with flash. If you consider doing some tests, it is important to remember that damage to colonies can occur if unsafe dosage-temperature combinations are used. It is important to repeat that weak colonies could find it difficult to put up with the dosages found to be secure at the end of the season for normal colonies. Based on our findings as well as on European literature on the subject, for a first Spring trial, the dosage at 20oc should not exceed 2 ml per frame of bees (8). Again, this experiment should at first be conducted with a small number of colonies.

We could not evaluate the efficiency of flash against tracheal mites as we do not have tracheal mites.

A very quick test also confirmed the possibility of using 85% formic at temperatures around 10. We can look forward to a still greater efficiency when colonies are broodless in October. The possibility of using oxalic in November as a complementary treatment, like it is done in Switzerland and other European countries, is also very promising. We tried that combination and we will be reporting on that on our web site.

We hear that the use of formic may soon be illegal or only authorized through restricted approved methods, if not a single one. It would be imperative that the use of the flash method of application be made legal as all other good methods. While the chemical solutions are getting exhausted, the beekeepers need a good toolbox to be able to build efficient IPM strategies.

Internet links on the subject:

Instructions pour l’utilisation ponctuelle de l’acide formique
Centre suisse de recherches apicoles

Short Term Treatment with Formic Acid
Wolfgang Poehlmann

Guideline on Use of Formic Acid for Varroa Control
Ministère de l’agriculture de la Nouvelle Zélande

Other suggested reading:

Imdorf, Anton, Stratégie de lutte alternative contre Varroa destructor en Europe centrale (2003), in Colloque en apiculture, La lutte intégrée contre les parasitoses de l'abeille, Centre de référence en agriculture et agroalimentaire du Québec (vx 002)


  1. We used NJ Philips drench guns (20 and 30 ml models). They should be cleaned and lubricated after each use according to manufacturer’s instructions.
  2. Natural mortality was evaluated the day before the treatment and then two weeks after leaving time for the brood, that had been sealed at the time of application, to hatch.
  3. We could not submit the fall honey from these colonies to a residue analysis. PMRA's "note to CAPCO" on formic acid suggests waiting 2 weeks after a formic application before honey supers are put on. It has to be mentioned that this note was a proposal to schedule formic acid, but that formic was finally never "scheduled". Any use of formic to treat colonies presently falls into a "gray zone" and clarifications are expected by the beekeeping industry.
  4. The product used was Thymovar®. It has been used according to the manufacturer’s specification for a period of 4 weeks.
  5. A fourth application of Mite Wipe had been initially planned for this group it had to was replaced by a flash treatment. The reason for this change was to be able to complete the last application of formic for all hives within the small window of mild weather offered by nature at that time.
  6. The remaining brood at that moment can be evaluated at 2 or 3 frames on average (more or less 600 sq. cm).
  7. The APINOVAR board we used has an entrance 1 cm x 37 cm, i.e. half the size of a normal entrance.
  8. This is the dosage we suggest with APINOVAR bottom boards.
  9. Recommandations formulated by the "Centre suisse de recherches apicoles" suggest 30 as a maximum daily natural mortality level just before the Fall treatment is started. It is also suggested that the natural mortality level should be reduced to ½ varroa daily before the winter.