<b>Pesticide-exposed bees fail to thermoregulate leading to cold colonies with consequences for offspring development</b>

Insects face multiple environmental stressors, including widespread pesticide exposure under climate change. Thermoregulation is a critical adaptive response to changing environmental temperatures, but if pesticide exposure were to impair this homeostatic process, reproduction and population viability may be at risk. This is of significant relevance to the ecologically important social insects, as multiple individuals must act collectively to maintain brood temperature for the successful rearing of offspring. In this study, we tested if pesticide exposure affects the ability of bumblebee individuals to maintain body temperature, whether such impact translates to reduced colony-level function (brood care and nest thermal homeostasis), and if this consequently impacts offspring development. Conducting three complementary experiments exposing bumblebees to a neonicotinoid pesticide under different temperature challenges, we show: first, that pesticide-exposed individuals cannot maintain a stable thorax temperature especially at lower temperatures. Second, individual reductions in body temperature are accompanied by behavioural changes and that pesticide-exposed colonies fail to maintain appropriate brood temperatures. Third, the impairment to brood thermoregulation (and not the pesticide toxicity to offspring <i>per se</i>) leads to delayed pupal development and reduced adult population growth rate. We provide a valid mechanistic explanation for why terrestrial insects requiring brood thermoregulation have shown signs of decline over the past few decades. With pesticide exposure landscapes being commonplace, and extreme weather events forecasted to become more frequent, our findings have concerning implications for the ability of populations to adequately respond, persist, and grow under current pesticide use regimes with ramifications on pollination services.昆虫面临多重环境胁迫，其中包括气候变化背景下广泛存在的农药暴露。体温调节（thermoregulation）是应对环境温度变化的关键适应性响应，但倘若农药暴露会损害这一稳态过程，昆虫的繁殖与种群生存力或将面临风险。这对具有重要生态价值的社会性昆虫尤为关键，因为这类昆虫需通过群体协作维持巢内幼体的温度，以成功繁育后代。 本研究通过三项互补实验，在不同温度胁迫条件下让熊蜂暴露于新烟碱类农药（neonicotinoid），结果显示：其一，接触农药的熊蜂个体无法维持稳定的胸部温度，在低温环境下该缺陷尤为突出；其二，个体体温降低的同时伴随行为模式改变，且接触农药的蜂群无法维持适宜的幼体巢温；其三，幼体体温调节功能受损（而非农药对幼体的直接毒性本身）会导致蛹发育延迟，并降低成虫种群增长率。 本研究为过去数十年间依赖幼体体温调节的陆生昆虫种群出现衰退迹象提供了合理的机制性解释。鉴于当前农药暴露已极为普遍，且极端天气事件预计将愈发频繁，我们的研究结果警示：在现行农药使用方案下，昆虫种群的有效响应、种群存续与增长能力或将受到显著影响，进而对授粉服务生态系统产生连锁效应。