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. It is critical to understand how exposure patterns influence the effects of pesticides so that we can improve environmental risk assessments and how we develop new compounds. 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 that target the same neural receptors: acetamiprid, clothianidin, and sulfoxaflor. Gene expression profiling enabled us to compare the effects of these treatments on the brain in a high-resolution manner. Surprisingly, acute and chronic exposure schemes affected largely non-overlapping sets of genes: acute exposure caused distinct regulatory changes in cellular and molecular processes, rather than amplifying the effects of prolonged low-dose exposure. In contrast, different pesticides under the same exposure scheme showed more comparable effects than the same pesticide under different exposure scheme. These findings show that the mode of exposure critically determines the effects of pesticides. Our results thus challenge the common practice of extrapolating toxicity measures from one exposure scenario and signal the need for more sensitive toxicity testing practices.