Harmful effects in vivo of formic acid on honey bee brood development evaluated with AI-based HiveAnalyzer© software

In apiculture, the natural acaricide formic acid (FA) is considered highly effective in killing Varroa mites, including their reproductive phase, which takes place in capped brood cells. It is recommended for long-term treatment in integrated pest management programs around the world. Using AI-based computer technology, we assessed potentially harmful effects of FA (60%) on brood development after 6 days of continuous treatment. A single in-hive application of FA had negative effects on the presence of eggs, young, and old larvae. All the developmental stages in open brood were strongly reduced after the FA treatment, whereas continuous presence of eggs and young larvae throughout the entire test period was observed in the control group. The computer analysis revealed changes in reproductive performance regarding egg laying and brood rearing in colonies treated with FA. The areas of empty cells decreased to 22% in the FA treatment group, whereas in the control, they increased to 46% at Brood Area Fixing Day (BFD) +22, thus indicating colony expectation of continuous egg laying in the next period.