Developmental exposure to pesticide contaminated food impedes bumblebee brain growth predisposing adults to become poorer learners

Abstract

Understanding the risk to biodiversity from pesticide exposure is a global priority. For bees, an understudied step in evaluating pesticide risk is understanding how pesticide contaminated foraged food brought back to the colony can affect developing individuals. Provisioning bumblebee colonies with pesticide (neonicotinoid) treated food, we investigated how exposure during two key developmental phases (brood and/or early-adult), impacted brain growth and assessed the consequent effects on adult learning behaviour. Using micro-computed tomography ({micro}CT) scanning and 3D image analysis, we compared brain development for multiple neuropils in workers 3 and 12-days post-emergence. Mushroom body calyces were the neuropils most affected by exposure during either of the developmental phases, with both age cohorts showing smaller structural volumes. Critically, reduced calyces growth in pesticide exposed workers was associated with lower responsiveness to a sucrose reward and impaired learning performance. Furthermore, the impact from brood exposure appeared irrecoverable despite no exposure during adulthood.