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Test Results For the Nassenheider Evaporator Using Formic Acid

The document reproduced below is as supplied with a device in 1998, the layout is due to myself, the words have had additions from other documents, but the sense is unchanged. Alterations and additions are italicised, but the original words have been left as well.

The prototype of the "Nassenheider evaporator" was tested by Dr. Eva Rademacher, a beekeeper... B. Polaczek and Prof. B. Schricker, Department of Zoology, Free University of Berlin, Königin-Luise-Str. 1-3, D-14195 Berlin, Germany. Here follows the report in parts:

Application of formic acid by means of a specially designed applicator (evaporator) results in an elimination of more than 90 per cent varroa mites without the mischievousness (problems) like loss of queen or hatching (emerging) honey bees and incalculable variations of efficacy.

The applicator was tested in two, steps:
I. Colonies in one-story-hives single brood box, standardized as to size quantity of bees and brood, were tested comparably. Aiming for to establish the effect of formic acid on bees and mites (free and in capped brood-cells) in July and September. Furthermore, the minimal effective dose was determined in September.

II. Regular colonies in two-story-hives as kept in apiaries were tested in order to determine a practicable procedure of treatment recommendable to the beekeeper. These tests were carried out from September until the end of the breeding season.

I. Standardized colonies (one story)

The amount of formic acid evaporated per 24 hours is presented separately in tests during July and September... Evaporation of the total amount of formic acid took place within 4.7 days (mean). The daily evaporation averaged 18.3 g/24 hours with reaches (maximums) up to 30 g/24 hours within the initial three days. In September total evaporation took up to 13 days at a daily mean rate of 7.8 g.

The counts of dead mites from adult bees reached 89.0 per cent (min. 53.3 per cent, max. 97.4 per cent) during the month of July, and, 95.9 per cent during September (min. 84.6 per cent, max. 99.6 per cent), respectively. Mites parasitical inside of capped brood-cells were killed during treatment at a rate of 87.6 per cent during summer (min. 61.5%, max. 94.1%), and, 91.5% (min. 86.4%, max. 100%) during fall, respectively.

In summary: The acaricidal efficacy of formic acid on mites of all stages averages 88.9% in July and 95.7% in September. Sufficient results derive from dosages of > 15 g/24 hours during summer and from > 6 g/24 hours during fall.

Determination of minimal dosage: For twelve days each one-story-colony was provided with an applicator containing 85 g of 60%-formic acid which evaporated from a felt area of 9 cm2.
The total amount of acid evaporated during this period of time differed. It averaged only 3.93 g/24 hours (min. 2.22 g, max. 5.3 g).
At this rate mite mortality was considerably lower and insufficient: Mean is 50.3% (min. 13.4%, max. 90%).

II. Not standardized-colonies (two stories)

The daily average was 17.5 g (min. 10 g, max. 34 g). The time span of treatment averaged 11.6 days (min. 5 days, max. 11.6 days).
The drop of dead mites averaged 94.3%, max. 99.8%. In 40% of the colonies > 98% of the mites where eliminated. A dosage of > 12 g/24 hours resulted in a efficacy of > 85%. This is in confirmation with the results obtained from standardized one-story-colonies (> 6 g/24 hours).

Calculated over the period of treatment the amount of evaporated formic acid per 24 hours should not be lower than 12 g/24 hours.
Damage on workers or queens was not observed in both (either) series of tests. The bees were hardly disturbed even at the beginning of the treatment, and they scarcely clustered in front of the hive. They did not hesitate to build combs incorporating the applicator. Mortality of bees was extremely low and peaked in one case at 6 bees during the period of treatment. This means a mortality of about 0.03%/colony.


The results presented prove a successful and very effective application of formic acid by using an evaporator as described. Due to a soft, but steady evaporation of formic acid an otherwise experienced loss of queens and worker bees is avoided.
The dosage to be evaporated per 24 hours and hive-story should range between > 6 g and 10 grams. The total amount of formic acid should be applied over a period of about 10 days and be 85 grams per story.
Due to its efficacy on mites even in capped brood-cells formic acid can be applied right upon final removal of the honey combs, thus initiating the development of healthy winter bees. A treatment upon final removal of honey combs and repeated in September should be efficient to secure the survivability of the colonies. As to this a long term test is under way.

I nether endorse, nor condemn, the use formic acid, in this semi controlled way, for the treatment of varroa infestation in honey bee colonies. This information is provided for those that wish to read it.

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