Glufosinate-P Herbicide Disrupts Gut Microbiota and Metabolism, Driving <i>Osmia excavata</i> Population Decline

Solitary bees face overlooked herbicide risks. <i>Osmia excavata</i>, a key early spring solitary bee, is especially vulnerable during soil-contact nesting, which coincides with peak herbicide use. We evaluated sublethal effects of glufosinate-P on <i>O. excavata</i>. After 15-day exposure, 5-50 mg/L glufosinate-P significantly reduced survival (by 25.00-57.50%) and food intake (by 24.95-49.95%; <i>P</i> < 0.05). High-dose (50 mg/L) exposure disrupted gut microbiota, increasing pathogenic <i>Serratia marcescens</i> and depleting beneficial microbes. Metabolomics showed systemic dysfunction, with a 32.18% reduction in glutamate disrupting amino acid metabolism, biosynthesis and nutrient transport, closely associated with microbiota shifts. The dual stressors of pathogen enrichment and metabolic paralysis compromised individual fitness and colony resilience, establishing a mechanistic pathway for population decline. Glutamate depletion emerged as a key biomarker connecting glufosinate-P exposure to systemic metabolic disturbance in nontarget pollinators. These findings underscore the need to reassess herbicide practices and integrate solitary bees into pesticide risk assessments to protect pollination.