Acute 24h oral LC₅₀ of CuSO₄ in newly emerged worker honey bees (Apis mellifera)

Honey bees (Apis mellifera) are essential pollinators for ecosystem functioning and agricultural production; however, agrochemicals and environmental contaminants can pose acute and chronic risks to bee health. Here, we assessed the 24 h acute oral toxicity of copper sulfate pentahydrate (CuSO₄·5H₂O), widely used in agriculture, in newly emerged (0-day-old) worker honey bees under laboratory conditions and estimated lethal concentration (LC) values using probit regression. Newly emerged workers from a single colony were used; bees were housed in plastic cages (10 bees per cage) and maintained at 25 ± 2 °C and ≥50% relative humidity. Throughout the experiment, bees were fed ad libitum with 50% (w/v) sucrose solution. Fresh CuSO₄·5H₂O solutions were prepared daily in 50% (w/v) sucrose solution. A range finding test screened 50–10,000 ppm, and the definitive test included 4500, 5000, 5250, 5500, 5750, 6000, 6500, and 7000 ppm to bracket the LC₅₀ region. Each concentration and the control were tested in triplicate (27 cages in total), and mortality was recorded hourly. Mortality data were analysed using probit regression in IBM SPSS Statistics 29.0. The estimated 24 h LC₅₀ was 4711 ppm (95% CI: 4309–4952). The LC₅, LC₁₀, LC₂₀, LC50 and LC₉₀ values were 3006, 3383, 3839, 4711 and 6040 ppm, respectively. Mortality increased consistently with concentration, indicating a clear acute dose–response relationship for CuSO₄·5H₂O. The findings presented herein contribute quantitative baseline data for the risk assessment of copper-based agrochemicals with respect to acute oral exposure in newly emerged worker honey bees.