What do pesticides do to bumble bee brains over time?

Bee on a purple flower

Pesticides, widely used to protect crops from pests, often unintentionally harm pollinators like bumble bees. The new study, published in BMC Biology, investigated the effects of three common pesticides - acetamiprid, clothianidin, and sulfoxaflor - on the brains of bumble bees.  

By analysing gene activity in both healthy and pesticide-exposed bumble bee brains, researchers from Queen Mary University of London and Imperial College London uncovered startling insights into how these chemicals alter brain function. The findings reveal a striking difference between short-term, high-level exposure (acute) and long-term, low-level exposure (chronic), shedding new light on the hidden danger pesticides pose to these crucial pollinators. 

The results show that bees’ responses to these chemicals depend mainly on how they are exposed, rather than the type of pesticide. Acute exposure triggers a surge in stress-response genes, while chronic exposure disrupts genes linked to immune function and energy production. As the old adage goes, “the dose makes the poison,” but this research shows it’s the timing of exposure that truly defines its impact. 

Current toxicity tests focus almost exclusively on acute exposure, yet bees in the wild are far more likely to face prolonged, low-level exposure. This mismatch means today’s testing methods are missing critical details. For instance, while traditional tests measure mortality rates, the study found that both acute and chronic exposure can be deadly, but through entirely different biological mechanisms. This raises serious questions about whether current regulations are fit for purpose. 

Dr Alicja Witwicka from Queen Mary University of London, lead author of the study, stressed: “Our study reveals the complexity of pesticide effects on pollinators, showing that the type of exposure critically determines the molecular impacts. This calls for regulatory frameworks that differentiate between and account for these differences.” 

Yannick Wurm, Professor in Evolutionary Genomics and Bioinformatics at Queen Mary University of London added: “Our results highlight how genomic tools can uncover hidden effects of environmental stressors, paving the way for more comprehensive and realistic pesticide safety assessments.” 

While some chronic toxicity tests have been introduced in recent years, this study underscores the need for a deeper dive into how varying exposure times and doses shape bees’ responses. By harnessing cutting-edge techniques like transcriptomics, regulators could unlock a clearer picture of pesticides’ hidden effects and finally take steps to safeguard these vital pollinators.