Glyphosate affects larval gut microbiota and metamorphosis of honey bees with differences between rearing procedures

Early exposure to glyphosate during larval development induces late behavioural effects on adult honey bees

As the most abundant pollinator insect in crops, Apis mellifera is a sentinel species of the pollinator communities. In these ecosystems, honey bees of different ages and developmental stages are exposed to diverse agrochemicals. However, most toxicological studies analyse the immediate effects during exposure. Late effects during adulthood after early exposure to pollutants during larval development are poorly studied in bees. The herbicide glyphosate (GLY) is the most applied pesticide worldwide. GLY has been detected in honey and beebread from hives near treated crops. Alterations in growth, morphogenesis or organogenesis during pre-imaginal development could induce late adverse effects after the emergence. Previous studies have demonstrated that GLY alters honey bee development, immediately affecting survival, growth and metabolism, followed by late teratogenic effects. The present study aims to determine the late impact on the behaviour and physiology of adult bees after pre-imaginal exposure to GLY. For that, we reared brood in vitro or in the hive with sub-chronic exposure to the herbicide with the average detected concentration in hives. Then, all newly emerged bees were reared in an incubator until maturity and tested when they became nurse-aged bees. Three behavioural responses were assessed as markers of cognitive and physiological impairment. Our results show i) decreased sensitivity to sucrose regardless of the rearing procedure, ii) increased choice latency and locomotor alterations during chemotaxis and iii) impaired associative learning. These late toxicity signs could indicate adverse effects on task performance and colony efficiency.

Synergistic effects between microplastics and glyphosate on honey bee larvae

Microplastic (MPs) pollution has emerged as a global ecological concern, however, the impact of MPs exposure, particularly in conjunction with other pollutants such as glyphosate (GLY) on honey bee remains unknown. This study investigated the effects of exposure to different concentrations of MPs and their combination with GLY on honey bee larvae development, or during the larvae period, regulation of major detoxification, antioxidant and immune genes, and oxidative stress biomarkers. Results revealed that combined exposure to MPs and GLY decreased larvae survivorship and weight, while exposure to MPs alone showed no significant differences. Both MPs and GLY alone downregulated the defensin-1 gene, but only combined exposure with GLY downregulated the hymenoptaecin gene and increased catalase enzyme activity. The data suggest a synergistic effect of MPs and GLY, leading to immunosuppression and reduced larvae survival and weight. These findings highlight potential risks of two prevalent environmental pollutants on honey bee health.

Enhancing knowledge of chemical exposures and fate in honey bee hives: Insights from colony structure and interactions

Honey bees are unintentionally exposed to a wide range of chemicals through various routes in their natural environment, yet research on the cumulative effects of multi-chemical and sublethal exposures on important caste members, including the queen bee and brood, is still in its infancy. The hive's social structure and food-sharing (trophallaxis) practices are important aspects to consider when identifying primary and secondary exposure pathways for residential hive members and possible chemical reservoirs within the colony. Secondary exposures may also occur through chemical transfer (maternal offloading) to the brood and by contact through possible chemical diffusion from wax cells to all hive members. The lack of research on peer-to-peer exposures to contaminants and their metabolites may be in part due to the limitations in sensitive analytical techniques for monitoring chemical fate and dispersion. Combined application of automated honey bee monitoring and modern chemical trace analysis techniques could offer rapid progress in quantifying chemical transfer and accumulation within the hive environment and developing effective mitigation strategies for toxic chemical co-exposures. To enhance the understanding of chemical fate and toxicity within the entire colony, it is crucial to consider both the intricate interactions among hive members and the potential synergistic effects arising from combinations of chemical and their metabolites.