Pesticide-exposed bees fail to thermoregulate leading to cold colonies with consequences for offspring development

ABSTRACT For many organisms, effective thermoregulation is needed to cope with changing environmental temperatures. But if exposure to pesticides in the environment were to impair this homeostatic process, reproduction and population viability could be at risk. Focusing on an important insect pollinator, we conducted three complementary experiments exposing bumblebees to a pesticide under different temperature challenges and measuring the impacts on thermoregulatory ability and brood development. First, we reveal that pesticide-exposed individuals cannot maintain a stable thorax temperature, especially at lower temperatures. Second, reductions in body temperature are accompanied by behavioural changes and that pesticide-exposed colonies fail to maintain appropriate brood temperatures. Third, such collective impairment on brood thermoregulation (not the pesticide toxicity to offspring per se) leads to delayed pupal development and reduced adult population growth. Our study provides a valid mechanistic explanation for why terrestrial insects requiring brood thermoregulation have declined. With frequent extreme weather events forecasted, our findings have concerning implications for how populations will adequately persist and grow under current pesticide-use regimes with ramifications on pollination services. Competing Interest Statement The authors have declared no competing interest. Footnotes ↵4 joint first authors