Acute and chronic pesticide exposure trigger fundamentally different molecular responses in bumble bee brains

Beneficial wild insects including pollinators encounter various pesticide exposure conditions, from brief high concentrations to continuous low-level exposure. To effectively assess the environmental risks of pesticides, it is critical to understand how different exposure patterns influence their effects. Unfortunately, this knowledge remains limited. To clarify whether different exposure schemes disrupt the physiology of pollinators in similar manners, we exposed bumble bees to acute and chronic treatments of three different pesticides: Acetamiprid, clothianidin, and sulfoxaflor. Gene expression profiling enabled us to compare the effects of these treatments on the brain in a high-resolution manner. There were two main surprises: First, acute and chronic exposure schemes affected largely non-overlapping sets of genes. Second, different pesticides under the same exposure scheme showed more comparable effects than the same pesticide under different exposure schemes. Acute exposure caused up-regulation of stress response mechanisms causing distinct regulatory changes, rather than amplifying the effects of prolonged low-dose exposure that affected predominantly immunity and energy metabolism. These findings show that the mode of exposure critically determines the effects of pesticides. Our results signal the need for safety testing practices to better consider mode-of-exposure dependent effects and suggest that transcriptomics can support such improvements.