Toxicological Effects of Cadmium Exposure on Larval and Adult Worker Honey Bees (Apis mellifera): Impacts on Survival, Gut Integrity, Microbiota, and Gene Expression

Cadmium (Cd) is a widespread environmental pollutant that threatens pollinators. This study examined the effects of Cd on survival, tissue accumulation, gut structure, microbiota, and gene expression in larval and adult worker honey bees (Apis mellifera). Larvae received diets with 0–1.25 mg/kg Cd, and adults were fed 0–4 mg/kg Cd in sucrose solution. Survival, Cd accumulation, gut histology, microbiota composition, and transcriptomic responses were assessed. Cd exposure reduced larval survival, pupation, and eclosion in a dose-dependent manner and decreased adult survival at the highest concentration. Cd accumulated in both stages, including brain tissue, and caused gut tissue damage. Adult gut microbiota showed increased Gilliamella abundance at high Cd levels. Transcriptomic profiling revealed upregulation of detoxification and immune genes in larvae and stress-response genes in adults. Larvae were more sensitive than adults, and Cd exposure impaired survival, gut integrity, microbiota balance, and gene expression, offering insights for ecological risk assessment of heavy metal pollution in pollinators.