Formic acid fumigator for controlling varroa mites in honey bee hives

The 50% formic acid fumigator (FAF) for varroa mite control was developed as part of a SARE grant (1999–2001). The fumigator was evaluated for five years on 123 colonies in five bee yards in Connecticut, Maryland and West Virginia (USA). Treatments eliminated all mites on adult bees and 90–95% of mites in sealed brood cells. Very few brood or new young adult bees were injured by the treatment. The fumigator is a simple design and the overall cost of treatment is about $1.00 per hive, or less. The 50% FAF was less toxic to bees compared to other treatments using 65%, 80% or 90% formic acid. The fumigator was applied for 18–24 hours when ambient temperatures were between 15–30°C. In the USA, one treatment in mid-August to mid-September was effective and usually all that was required each year. The 50% FAF used with other essential oil treatments including salt-grease patties with wintergreen, feeding 1:1 syrup with Honey-B-Healthy® (spearmint and lemongrass essential oils), and use of screened bottom boards, together provide a synergistic effect to keep mite numbers at a relatively low level, as part of an integrated pest management (IPM) system.