OECD bumblebees with dimethoate and future alternatives

SETAC Europe 2025 -- Assessing the acute toxicity of pesticides on non-target species, particularly bees, is essential for evaluating environmental risks. The absence of defined concentration ranges and shorter time endpoints in bumblebee tests limits precise health assessments and control chart establishment. Both honeybee and bumblebee tests express LC50 in µg/bee. However, bumblebee tests require individual bee weight measurements without adjusting LC50 values per µg/mg, increasing resource use and costs without clear application. Both honeybee and bumblebee tests used dimethoate as reference item. Dimethoate was banned by the European Commission in 2019 due to environmental and health concerns. The objectives of this study were to determine 24-hour dimethoate toxicity endpoints in bumblebee assays to assess bee batch validity, generate a weight acceptance range to give purpose to weight measurements, and start a discussion of alternatives to dimethoate as a reference item.