COMMERCIAL 2,4-D FORMULATION AMINOL® 806 IMPAIRS IN VITRO-REARED HONEY BEE LARVAL DEVELOPMENT AND SURVIVAL

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INTRODUCTION: 2,4-dichlorophenoxyacetic acid (2,4-D) is an extensively used agricultural herbicide that can contact non-target organisms through direct (e.g., application) or indirect (e.g., drift) exposure. Risk assessment data demonstrate the hazards of pesticides to honey bees (Apis mellifera), corroborating field evidence that agrochemical exposure contributes to global pollinator population declines. Understanding the effects of 2,4-D on honey bee larvae is essential to identify developmental vulnerabilities with potential long-term impacts on colony health. OBJECTIVES: This study aimed to evaluate the acute dietary toxicity of AMINOL® 806, a commercial 2,4-D formulation, on honey bee larvae using an in vitro rearing system to determine single-dose effects on larval development and survival. MATERIALS AND METHODS: On day 4 post-grafting, in vitro-reared larvae were exposed to single acute doses of 2,4-D (5, 10, 25, 50, 75, and 100 μg a.i./larva) via contaminated diet. Mortality (n = 24 larvae/group) was assessed daily until day 7, and body weight of surviving larvae (n = 6/group) was measured on day 7 (final day of larval development). Survival rates were calculated as the percentage of surviving individuals relative to the initial cohort size. Body weight data were analyzed by one-way ANOVA followed by Tukey’s post hoc test. Results are presented as mean ± SEM, with statistical significance set at p < 0.05(*). RESULTS AND CONCLUSION: The results demonstrated 100% mortality by day 7 at the highest concentrations (75 and 100 μg a.i./larva), while the lowest mortality rate (12.5%) occurred at 5 and 10 μg a.i./larva. The 25 μg a.i./larva dose resulted in 37.5% mortality, whereas 50 μg a.i./larva caused 62.5% mortality. Therefore, for subsequent LD50 determination, doses between 25–50 μg a.i./larva will be employed. Exposure to 2,4-D induced dose-dependent reductions in larval body weight across all concentrations, with the greatest weight decrease observed at the highest dose (47.41 ± 6.279%). The commercial 2,4-D formulation AMINOL® 806 poses significant risks to honey bee populations, inducing both lethal effects and sublethal developmental impairments that may compromise colony sustainability.