ORIGINAL ABSTRACT

Microplastics, as emerging persistent environmental contaminants, can act as vectors for the absorption of other pollutants in ecosystems, such as pesticide residues. However, the combined toxicological effects of microplastics and pesticides on pollinators remain poorly understood. Here, we evaluated the toxicity of polystyrene microplastics (PS) and glyphosate (GLY), both individually and in combination, in honeybees (Apis mellifera). While no significant changes in body weight gain or food consumption were observed after 20 days of exposure, co-exposure to PS and GLY significantly increased bee mortality and induced midgut damage and microbial dysbiosis. In the gut, pathways associated with cell proliferation and differentiation, along with genes related to oxidative stress, detoxification, and immunity, were significantly downregulated. Furthermore, the combination of PS and GLY impaired sucrose responsiveness, a key cognitive behavior in bees. Brain transcriptomics indicated a downregulation of serotonergic synapse-related genes, which were correlated with shifts in core gut bacteria such as Snodgrassella and Lactobacillus. Our findings demonstrate that co-exposure to PS and GLY exacerbates gut homeostasis disruption and impairs cognitive behavior, suggesting a potential role of the gut-brain axis. This study extends our understanding of the combined ecological risks posed by multiple environmental contaminants to bees as insect pollinators and emphasizes the need for comprehensive hazard assessments in insect conservation.