Honey bees are commonly co-exposed to pesticides during crop pollination, including the fungicide captan and neonicotinoid insecticide thiamethoxam. We assessed the impact of exposure to these two pesticides individually and in combination, at a range of field-realistic doses. In laboratory assays, mortality of larvae treated with captan was 80–90% greater than controls, dose-independent, and similar to mortality from the lowest dose of thiamethoxam. There was evidence of synergism (i.e., a non-additive response) from captan-thiamethoxam co-exposure at the highest dose of thiamethoxam, but not at lower doses. In the field, we exposed whole colonies to the lowest doses used in the laboratory. Exposure to captan and thiamethoxam individually and in combination resulted in minimal impacts on population growth or colony mortality, and there was no evidence of synergism or antagonism. These results suggest captan and thiamethoxam are each acutely toxic to immature honey bees, but whole colonies can potentially compensate for detrimental effects, at least at the low doses used in our field trial, or that methodological differences of the field experiment impacted results (e.g., dilution of treatments with natural pollen). If compensation occurred, further work is needed to assess how it occurred, potentially via increased queen egg laying, and whether short-term compensation leads to long-term costs. Further work is also needed for other crop pollinators that lack the social detoxification capabilities of honey bee colonies and may be less resilient to pesticides.

蜜蜂在作物授粉过程中通常同时接触农药，包括杀菌剂克菌丹和新烟碱类杀虫剂噻虫嗪。我们评估了在一系列实际剂量下单独和组合接触这两种农药的影响。在实验室测定中，克菌丹处理的幼虫死亡率比对照高 80-90%，与剂量无关，与最低剂量噻虫嗪的死亡率相似。有证据表明，在最高剂量的噻虫嗪下，克菌丹-噻虫嗪共同暴露会产生协同作用（即非相加反应），但在较低剂量下则不会。在现场，我们将整个菌落暴露于实验室使用的最低剂量。单独或联合接触克菌丹和噻虫嗪对种群增长或群体死亡率的影响极小，并且没有证据表明存在协同或拮抗作用。这些结果表明克菌丹和噻虫嗪均对未成熟的蜜蜂有剧毒，但整个蜂群有可能补偿有害影响，至少在我们的田间试验中使用的低剂量下，或者田间实验的方法差异影响了结果（例如，用天然花粉稀释处理）。如果发生补偿，需要进一步的工作来评估它是如何发生的，可能是通过增加蜂王产卵，以及短期补偿是否会导致长期成本。对于其他缺乏蜂群社会解毒能力并且对农药的抵抗力可能较差的作物授粉媒介，还需要开展进一步的工作。