Flupyradifurone and nutritional stress reduce solitary bee fitness

Exposure to flupyradifurone (FPF) significantly reduces survival, reproduction, and foraging efficiency in the solitary bee *Osmia bicornis*, especially under nutritional stress. Field-realistic conditions with buckwheat monocultures led to 29-fold higher mortality in FPF-treated bees within 24 hours. Nutritional stress exacerbates FPF’s negative effects on flight activity, duration, and flower visitation. The study reveals critical gaps in current pesticide risk assessments that overlook multi-stressor interactions. Using 432 marked bees in 54 m² flight cages with buckwheat, wild mustard, or purple tansy, half treated with FPF, results show FPF’s underestimated toxicity to solitary bees. Secondary metabolites in pollen, such as glucosinolates and phenolic compounds, may support detoxification. The findings call for holistic environmental risk assessments that include diverse pollinators and agroecosystem contexts, advocating for conservation of flower-rich habitats to mitigate pesticide impacts. Data available via Dryad.