Investigating the effects of glyphosate on the bumblebee proteome and microbiota

Glyphosate is one of the most widely used herbicides globally. It acts by inhibiting an enzyme in an aromatic amino synthesis pathway specific to plants and microbes, leading to view that glyphosate poses no risk to other organisms. However, there is growing concern that glyphosate is associated with detrimental health effects in humans, and an ever-increasing body of evidence suggests that glyphosate affects other animals including pollinating insects such as bees. Although pesticides have long been considered a contributing factor in the decline of wild bee populations most research on bees has focussed on demonstrating and understanding the effects (particularly sublethal ones) of insecticides. To assess whether glyphosate poses a potential risk to bees we characterised the changes in survival, behaviour, digestive tract proteome and microbiome in the bumblebee Bombus terrestris after chronic exposure to field relevant doses of glyphosate alone and as part of the commercially available product RoundUp Optima+®. Regardless of source, changes in response to herbicide exposure in important cellular and physiological processes in the digestive tract of B. terrestris were observed, with the abundances of proteins associated with oxidative stress regulation, metabolism, cellular adhesion, the extracellular matrix, and various signalling pathways being altered. Interestingly, endocytosis, oxidative phosphorylation, the TCA cycle, and carbohydrate, lipid, and amino acid metabolism were differentially altered depending on whether the exposure source was glyphosate AI or RoundUp Optima+®. In addition, RoundUp Optima+®, but not the active ingredient glyphosate, impacted fungal diversity in the digestive tract microbiota. Our research provides new insights into the potential mode of action and consequences of glyphosate exposure at the molecular and cellular levels in bumblebees and highlights issues with current regulatory measures involving commercial formulations of pesticides where the impact of the co-formulants on non-target organisms are generally overlooked.