Formic Acid Single Application
Efficacy Comparison Trials

Introduction and Background:

In 2002 NOD Apiary Products Ltd. (NOD), in conjunction with the Ontario Beekeepers Association (OBA) Tech Transfer Program (TTP), conducted four trials, spring, summer, early fall and late fall. These trials tested several hole configurations of perforated plastic pouches holding a fiberboard pad soaked with 65% formic acid. The goal was to determine the most effective top-of-hive single application method having minimum impact on colony health but with maximum kill of the entire varroa population.

The research conducted under a permit from Canada’s Pest Management Regulatory Agency (PMRA) was reviewed by a Health Canada auditor from Guelph. As well, two pesticide reviewers from PMRA offices in Ottawa came to trial sites to familiarize themselves with beekeeping industry equipment and terminology, and to examine test conditions, where the trials were being conducted. 

This is a quick overview of two of the trials, the warm weather (spring and early fall) trials, showing some of the development process for the Mite AwayII™ pad: 

Materials & Methods:

In order to determine the efficacy against the entire mite populations in the colonies trials were six weeks long: three weeks of formic acid treatment followed a three week wash of a hard chemical treatment of a known efficacy. Modified Pettis tests (Pettis et al.,1998) were performed by the OBA TTP personnel to assess varroa susceptibility to Apistan®. If the mite population was determined to be susceptible to Apistan®, it was used as the wash treatment. If resistance to Apistan® was determined, CheckMite+™ was used as the wash. Sticky boards were used to monitor varroa drop throughout the trials, each one being replaced and counted either daily or weekly. Colony mite loads were assessed by pre-treatment 24 hour natural mite drops and the colonies were divided up into test groups based on mite loads, colony strength, and number of brood chambers.

Standard Langstroth equipment was used, single and double brood chamber colonies. Bottom entrances were fully open, all other entrances were closed over. All treatments were on the brood chamber. 

The fiber board pad used contains no hazardous ingredients and will not produce toxins when combined with the formic acid. These pads were placed into plastic pouches with various holes punched in them, and the open ends sealed. Fifteen hole and hive configurations were tested. (see fig. 1). 250 ml of food grade 65% formic acid was injected into each pouch and absorbed by the pad. Pads were place on two ½ inch square, 4-inch long spacer sticks on the top bars. A 1½-inch spacer rim was placed on the hive to accommodate the ½ -inch space under the pad, the pad, and a ½-inch space over the pad.

Colonies, n=84, were monitored in the efficacy trials in Eastern Ontario (near Cornwall), Central Ontario (near Stirling) and Southwestern Ontario (near Smithville) in four beekeeping outfits, pre-screened to insure adequate mite loads. One colony collapsed from varroa load during the trials and one was culled out due to wind blowing off the hive cover. Colonies, n=112, were monitored for formic acid impact on colony health.

Terminology: in order to describe the effects of various treatments the following terminology is used:

• Cluster Shift: the bees abandon an area of brood and resume brood rearing elsewhere in the hive
• Brood burn: eggs and larva killed off
• Emerging brood burn: hatching bees killed by the formic vapors, seen partially emerged from the cells
• Hive vs. Colony: the hive is the equipment that contains the colony of bees. The colony is defined by the number of frames of bees. For example, a typical 6 frame spring colony would be 3-4 frames of worker brood with a frame on each side covered with bees on honey and pollen. If eggs were present it is presumed to be queenright.

Observations: Stronger colonies had less difficulty coping with formic acid. 6 to 20 frames of bees had minimum damage and maximum rebound. This was confirmed in spring 2003 by G. Wilson. Queen mortality was observed on single story colonies with four of the tested hole configurations: 30-¾ inch holes with holes down, 98- ¼-inch holes with 49 holes each side, 24- ¾ inch holes with 12 holes each side, and 128- ¼-inch holes with 64 inch holes on each side. Brood damage to the colony was not directly related to efficacy. There were some treatments with high brood damage but lower varroa kill than others with less brood damage. Single story colonies were more susceptible to damage than two story colonies. One colony, a single story hive, with 30 - ¾-inch holes, holes facing down test treatment, abandoned the hive and remaining brood and absconded. Surviving colonies saw great surges of egg laying by the end of the formic treatments. Colony strength was observed to be equal to or greater than the controls by the end of the six week trials.

The 90 - ¼-inch holes with the holes down showed the best balanced configuration between good efficacy and minimal damage. Although there was some brood burn, hatched larva was observed by day 7 of the treatments, so egg and larva damage was minimized to the first three days. No queen loss occurred. Some emerging brood burn was observed, but just in the area directly under the pad. Over half of the formic released was released in the first week of the treatment, charging the hive environment()(), which appears to be necessary for good efficacy. Colony strength was equal to or greater than the controls by the end of the trials. This hole configuration is currently undergoing government registration as Mite AwayII™.

From efficacy trials run in the summer of 2002 where the pads were placed over a honey super instead of on the brood chamber it was observed that the efficacy dropped dramatically. This was confirmed in trials conducted in Florida in January 2003.

Cluster shift was observed in smaller colonies. This was seen as a survival tactic, as the formic acid vapors were forcing the colony off the combs but not damaging the queen. Looking at the potential for using Mite AwayII™ on smaller colonies in the spring of 2003, cluster shift was imitated as a manipulation in the hive, before treatment by Mite AwayII™, by placing the frames of brood against an outside wall of the hive, then a frame of feed. Colonies as small as two frames of brood were monitored. The colonies were able to handle the formic acid vapors and developed into good hives by the end of the three week formic acid treatment. 

Conclusion: Hole placement, size and number, are critical to efficacy (see fig.1), rate of formic acid vapor release and colony health. The varroa kill data for the early fall warm weather trial was submitted to a University of Guelph statistician by the OBA TTP personnel for statistical analysis.  Analysis showed an efficacy of the 90-¼ inch holes on one side, holes oriented down, of “93.31 ± 5.50%… makes it suitable as a product to control varroa.” (see fig.2).

Last Updated May 16, 2008

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