Formic Acid Honey-B-Healthy Fumigator: We have been experimenting with formic acid treatments. Warning: Please be aware, this is not a recommendation for beekeepers to apply formic acid to their hives to control mites. Please contact your state apiarist for information on legal methods for controlling mites. We made 20 formic acid fumigators for treating hives with high mite numbers. We use an absorbent pad [Kendall undergarment, available from hospital supply stores or drugstores] at the top of the hive, protected from the bees by a plastic or aluminum screen on the underside, a heavy plastic sheet or aluminum flashing on the upper surface. [a sandwich of three layers, with the same x-y dimensions as a brood chamber] and spaced 3/4"[using wood molding] Above the top bars of the upper brood chamber. Bee ways, of 3/8" (.95cm) are left on the sides of the fumigator. We pour the formic acid, mixed with 10% Honey-B-Healthy [mixed fresh each time] onto the pad and place it on top of the brood chamber, with the absorbent material down. The amount of formic acid mix used depends on the number and depth of the brood chambers; eg., we use 2.8 ozs (85ml) for a single deep chamber and for two Illinois chambers [3.2 ozs or 95ml], and slightly more for a deep + Illinois [3.6 ozs or 110ml], etc. The fumigator is placed on the hive, on the upper brood chamber, for 24 hrs or less during warm to mild weather (19-30 C; 65-86 F). We reduce the entrance to 3.5" [ 8.9 cm] at the center. The bees quickly begin fanning the air through the brood nest and out of the small entrance, you can smell the formic acid coming out of the center entrance. This system works the best when colonies are strong with a lot of brood frames. The heat from the brood and activity (fanning) of the bees we believe causes the proper evaporation off the fumigator.
We measured the temperature of the air coming out of the entrance and it was nearly always 90°F (32.2°C). We get excellent mite kill on most colonies (91% in 16 hours), including mites inside sealed brood cells and we see very little interruption of queen performance, and a balled queen reduction from 25% to 5% (because of the HBH). In early experiments, we conducted similar trials with formic acid only (no HBH), at the same concentration and amount, and lost several queens (one out of four 25%). Queen losses were reduced by 22.6% using the HBHFA mix. To eliminate any queen losses we cage the queen and place her above the fumigator during the one or two day treatment period. The summer of 2002 we began to spray exposed bees on and between exposed brood supers along with the entrance with HBH sugar water spray (4 tsp. Per quart). This along with adding HBH to the 50% formic eliminated queen losses. We have recently eliminated adding HBH to the 50% formic had have been just spraying the bees with HBH (4 teaspoons per quart of 1:1 sugar water), and have had excellent results eliminating queen losses.
We always make up the solution in an open, outside area or in a fume hood, and we use a hydrometer to obtain exactly 50% (sp. grav. = 1.110). We use a hydrometer because we have found considerable variation in strength of formic acid in containers we purchased; some were off as much as 30%. This may be one reason that published reports give variable results for the use of formic acid. One must be aware too that formic acid obtained from some commercial sources may contain heavy metal contaminants--these could be harmful to the bees, to humans or to the environment. Always inquire about the possibility of heavy metal contaminants.

Please see our web site for a listing of specific gravities correlated with percent formic acid: http://rnoel.50megs.com/2000/chart.htm

We believe this new method of applying FA is effective for the following reasons: We have an air space just above the upper brood chamber; heat from the brood rises into this air space. The upper plastic or aluminum sheet prevents this warm air from being lost to upper supers. (We kept supers on during treatments in order to be able to test for FA in the honey above the fumigator). The FA is much heavier than air, so it has a tendency to sink, not rise. This is probably why so many investigators had variable results when placing pads of FA on the bottom board. So, the heat rises from the brood, activates the FA in the absorbent pad, causing evaporation. The bees respond with a roar of fanning, and the air circulates through the brood frames and eventually exits the small entrance opening (3/8"x3.5"). The circulated air is warm (90 F); the FA penetrates capped cells, killing mites inside, but not the brood. Within 24 hrs, virtually all FA is gone and the fumigator can be removed. We saw in all colonies, including 12 previously treated with Apistan, that mite drop occurred at a high daily rate for 13 days due to dead mites in the cells dropping from newly emerged bees. Some colonies produced counts exceeding 3,000 mites on a single board in 3 days. This number of 13 days (16 days for drones) corresponds to the number of days required for capped brood to complete development and exit the cells; as bees exit the cells, dead mites fall between the frames through the screened bottom, onto the detector board below.
Finding a handful of newly hatched bees (30 - 50), crawling in the front of the hive, after the treatment, is a good sign. This is a good indicator of a good mite kill in the cells as well as on the bees. The formic may cause damage to tender breathing tubes such as the trachea while these bees are under stress hatching. This is a minimal loss when compared to the thousands of young bees saved by killing the mites in the capped cells.

Note: Liquid Formic Acid is not an Approved Miticide in the U.S.A. Contact your State Apiary Inspector for approved treatments for Parasitic Mite control in honey bee colonies.