Consumption of pollen contaminated with field-realistic concentrations of fungicide cause sub-lethal effects in common eastern bumble bee (Bombus impatiens [Hymenoptera]: [Apidae]) microcolonies

Bumble bees are declining across the globe. Causes of this decline have been attributed to a variety of stressors, including pesticides. Fungicides are a type of pesticide that have been understudied in the context of bumble bee health. As a result, fungicides are often applied to flowering plants without consideration of pollinator exposure. Recent work demonstrates that fungicides have sublethal effects in bumble bees, but little is known about how much fungicide it takes to cause these sublethal effects. To address this gap in the literature, we fed microcolonies of the common eastern bumble bee (Bombus impatiens) pollen contaminated with a range of fungicide concentrations. We chose these concentrations based on the range of fungicide concentrations in pollen and nectar that were reported in the literature. Results revealed that later-stage pupae and newly emerged males are potentially sensitive to fungicide exposure, showing smaller size and reduced fat reserves at intermediate levels of contamination. Compared to the control, intermediated levels of fungicide-contaminated pollen led to increased pupal mortality and delayed male emergence. Contrary to expectations, higher fungicide levels did not exhibit a linear relationship with negative impacts, suggesting nuanced effects. Because body size and emergence timing are important aspects of bumble bee reproductive behavior, results have implications for mating success, potentially disrupting colony development.

全球范围内的熊蜂种群正持续衰减，其种群下降的诱因可归结为多种胁迫因子，其中包括农药类污染物。杀菌剂作为一类农药，在熊蜂健康相关研究中长期未得到足够关注。正因如此，杀菌剂常被直接施用于显花植物，却未考虑授粉昆虫的暴露风险。现有研究表明，杀菌剂会对熊蜂产生亚致死效应，但目前学界尚不清楚引发此类亚致死效应所需的杀菌剂剂量阈值。为填补这一研究空白，本研究以东方常见熊蜂（*Bombus impatiens*）的微型蜂群为实验对象，向其喂食携带有不同梯度杀菌剂浓度的花粉。实验所选用的浓度梯度，参考了已有文献中报道的花粉与花蜜内杀菌剂浓度范围。实验结果显示，晚期蛹与新羽化的雄蜂对杀菌剂暴露具有潜在敏感性：在中等污染浓度下，这些个体体型更小且脂肪储备量更低。与对照组相比，中等浓度的杀菌剂污染花粉会导致蛹死亡率升高，且雄蜂羽化时间延迟。与预期相悖的是，更高浓度的杀菌剂并未与负面影响呈现线性相关关系，这提示其作用效应存在精细的差异化特征。由于体型大小与羽化时间是熊蜂繁殖行为的关键特征，本研究结果将对交配成功率产生影响，或进一步干扰蜂群的正常发育。