Abstract
Varroa destructor remains a major threat to honey bee (Apis mellifera) health, requiring effective and sustainable control strategies. In this study, a formic acid-based product (Formic Pro™) was tested for its varroacidal efficacy and effects on hygienic behavior of honey bee colonies. Sixty hives were assigned to three groups: Formic Pro group (n = 30), Positive control treated with amitraz (n = 15), and untreated Negative control (n = 15). Efficacy was assessed by daily mite drop counts, while hygienic behavior was evaluated before and after treatment using the "pin-killed" brood method. The Formic Pro group achieved a mite mortality rate of 88.37% ± 0.23, while amitraz as a control exerted 94.30% ± 0.95 efficacy. The treatment was well tolerated, with no queen losses, minimal and transient brood effects, followed by brief bearding on the first day of trial. Hygienic behavior significantly increased in the Formic Pro group (PCC from 96.69% to 99.01%, p < 0.001), while it declined in the Negative control and remained unchanged in the Positive control group. These results demonstrate that the tested formic acid-based product provides high acaricidal efficacy which is tolerated well in colonies and that it stimulates a key behavioral defense mechanism through hygienic behavior, providing benefits both for Varroa control and colony resilience.