Holistic assessment of acute exposure to Bacillus velezensis on honey bee behaviour and flight performance

Biopesticides represent an eco-friendly alternative to synthetic pesticides; however, their impact on honey bees at the colony level remains poorly understood, and current regulatory protocols do not adequately address long-term sublethal effects. In this study, we investigated the sublethal effects of acute oral exposure to Bacillus velezensis (reclassified from B. amyloliquefaciens) on individual behaviour, social interactions, flight and foraging activity, and homing ability in Apis mellifera using a holistic approach. In-hive observations, based on scan sampling, were used to compare behavioural display between exposed and unexposed foragers. Additional behavioural observations were conducted at the hive-entrance using the all-occurrences sampling method to assess the effect of the biopesticide on flight performance, foraging activity, and homing ability. At the in-hive level, exposed foragers showed a significant shift in the locomotory activity, with increased walking and reduced inactivity compared with controls. At the hive-entrance, flight activity was significantly higher in exposed than in unexposed foragers. Conversely, social interactions, feeding behaviour, pollen foraging and homing ability, did not appear to be affected by exposure to the biopesticide. Overall, the observed changes at both individual (locomotory activity) and colony (flight activity) levels highlight the need to revise current evaluation protocols on a case-by-case basis, employing a holistic, multi-level approach.