Effects of lithium chloride on queen egg-laying performance and worker honey bee behavior.

BACKGROUND Lithium chloride (LiCl) has recently emerged as a potential treatment for Varroa in honey bee colonies, yet its effects on bee behavior remain poorly understood. This study investigates, for the first time, the impact of oral exposure to chronic 50 mM LiCl-administered via candy over 7-10 days-on three key behavioral traits: queen oviposition, worker brood care, and worker aggression. Laboratory assays were conducted using caged bees with ad libitum access to LiCl-enriched or control candy. RESULTS Egg-laying rates did not differ significantly between LiCl-treated and control groups. Worker bees exposed to LiCl showed a significant increase in mite mortality. Brood care behavior, assessed using a 4-day-old queen larva, was unaffected in terms of nursing frequency and duration. However, LiCl-treated workers exhibited a significant reduction in aggressive behaviors compared to controls. CONCLUSIONS LiCl did not adversely influence queen egg laying or workers' nursing behavior, reinforcing previous findings suggesting negligible long-term risks to essential colony maintenance activities such as queen reproductive performance and nursing behavior. The reduced aggression observation is consistent with reports from other species, suggesting a conserved modulatory role of Li on aggression across the animal kingdom. From an applied perspective, these results imply that LiCl can be used as Varroa control without compromise on colony reproduction and brood care. Furthermore, LiCl could potentially facilitate the management of aggressive colonies, thereby reducing stress for both the bees and their handlers. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.