Chemical Pollution and Pollinator Health: Assessing Multi-Stressor Effects on Honeybees and Solitary Bees

Chemical pollutants pose a significant threat to bee health, affecting their physiology, behavior, and survival. While the effects of specific insecticides on bees are well known, it is necessary to considered that bees are routinely exposed to complex mixtures of chemicals, including fungicides, herbicides, heavy metals, and veterinary drugs. The combined effects of these pollutants remain poorly understood, particularly their impacts at sublethal concentrations. Research on chemical exposure has largely been focused on honeybees, yet other pollinators, including solitary bees, also face similar risks. By integrating multiple stressors and diverse pollinator taxa, the study aims to expand our understanding of pollutant-pollinator interactions beyond the traditional honeybee model. A multidisciplinary approach has been adopted to provide valuable insights into bee survival considering and integrating information from different factors that are affected by pollutants. In particular, this research aims to evaluate effects of chronic oral exposure at sublethal concentration to different chemicals (boscalid, copper(II)chloride dihydrate; ivermectine and glyphosate) on survival of adults of the social honey bee ({Apis mellifera}) and the solitary red mason bee ({Osmia bicornis}), by integrating gut microbiome characterisation and different biomarker responses. As a result different chemicals impacted survival at different level. The gut microbial community of these pollinators was investigated by molecular analyses in terms of abundance and taxonomic composition, using quantitative PCR and high-throughput Illumina sequencing, respectively. Overall, the results indicate that all the administered chemicals, though to a different extent, affected the gut microbiome of bees in terms of community composition and diversity. As biomarkers, acetylcholinesterase, carboxylesterase, glutathione S-transferase, alkaline phosphatase, phenoloxidase and prophenoloxidase activities were evaluated, together with nuclear abnormalities assay and differential hemocytes count. In the solitary bee, detoxification processes were induced after both copper and boscalid+copper(II)chloride dihydrate treatments compared to control and boscalid ones. After ivermectine and ivermectine+glyphosate treatments, {Osmia bicornis} specimens showed metabolic alteration. Higher values of DNA damage were observed after all treatments, both alone and in combination. These findings will help refine environmental risk assessments and support conservation efforts to protect pollinators and their crucial ecosystem services.