Route-Dependent Toxicity and Ecological Selectivity of Melaleuca alternifolia Essential Oil in Apis mellifera...

The intensification of agricultural practices has led to an increase in the use of insecticides, raising concerns about the exposure of non-target organisms, particularly pollinators. In this context, plant-derived essential oils have been proposed as environmentally friendlier alternatives due to their low persistence; however, their toxicological effects on bees remain insufficiently characterized, especially with respect to different exposure routes. This study evaluated the toxicity of Melaleuca alternifolia essential oil to Africanized Apis mellifera worker bees under three exposure pathways: indirect spraying, direct spraying, and ingestion. The essential oil was tested at a concentration of 0.75% (v/v). Bee survival was analyzed using Cox proportional hazards models, while potential sublethal behavioral effects were assessed through vertical displacement and flight resumption assays. Indirect spraying and ingestion did not significantly affect worker survival compared with the control, indicating low toxicity under conditions simulating residual environmental or dietary exposure. In contrast, direct spraying caused an approximately 20% reduction in survival over the experimental period, demonstrating route-dependent toxicity, although mortality remained substantially lower than that observed for the positive control (fipronil). Behavioral assays showed no significant impairment of flight performance in surviving bees. Overall, the results indicate that the toxicity of M. alternifolia essential oil to A. mellifera is strongly influenced by the route of exposure, underscoring the importance of exposure pathways in environmental risk assessment. These findings contribute to understanding the physiological selectivity of botanical insecticides and provide relevant information for evaluating the safety of essential oils for pollinator protection in agroecosystems.