1. Hundreds of recent studies have voiced concern over the negative impacts of non‐target pesticides on pollinator health. However, pesticide loads are highly variable across agricultural landscapes and it is unclear whether pollinators exhibit behavioural responses (e.g. aversion) that mediate their exposure risk under realistic foraging environments.
2. We tested whether monarch butterfly Danaus plexippus adults and larvae base their oviposition and foraging decisions, respectively, on the presence and concentration of pesticide residues on their milkweed host‐plant, Asclepias syriaca. To do so, we experimentally simulated field‐realistic exposure for six of the most commonly detected pesticides—one insecticide, two herbicides and three fungicides—either alone or in combination. These laboratory and greenhouse manipulations experimentally paired an untreated control with the pesticides at their mean or maximum concentrations. Last, we used a two‐year field survey to correlate pesticide concentration on milkweed leaves with monarch oviposition.
3. Butterflies placed fewer eggs on milkweeds treated with a cocktail containing all six pesticides at their maximum concentrations, resulting in c. 30% less oviposition compared to the solvent control. Neonate (1st instar) larvae also showed a preference for pesticide‐free leaves in paired disc assays for four out of six compounds tested, with feeding aversion observed at both mean and maximum concentrations. Later instars did not show a comparable behavioural reaction to pesticide presence or concentration, but this could be partially due to the feeding‐deterrent properties of the acetone solvent used. In the field, per plant egg load was negatively correlated with increasing leaf concentration for one of the herbicides, metolachlor; although all pesticides tested showed similar oviposition trends.
4. Synthesis and applications. Our data provide evidence that monarchs are capable of adaptively adjusting their oviposition and foraging behaviours based on which pesticides are present on their host‐plants. Importantly, this preference was observed at field‐relevant concentrations, suggesting that monarchs behaviourally regulate pesticide exposure risk for their offspring by avoiding contaminated plants. Variability in pesticide identity and/or load among milkweeds within/between habitat patches should be considered in future restoration efforts aimed at attracting butterflies for larval development, as well as the relative importance of pesticides compared with other plant factors (e.g. genotype or species, developmental stage) known to affect oviposition. More broadly, this work illustrates some of the limitations of no‐choice trials and suggests that experimental designs embracing field‐scale heterogeneity in pesticide presence and concentration will lead to more realistic non‐target impact assessments and improved management.

中文翻译：

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传粉者是否喜欢无农药的植物？君主和马利筋的实验测试

1. 数百项近期研究对非目标农药对传粉者健康的负面影响表示关注。但是，农药含量在整个农业景观中变化很大，目前尚不清楚传粉媒介是否表现出行为反应（例如厌恶），以介导其在现实觅食环境下的接触风险。
2. 我们测试了帝王蝶Danaus plexippus成虫和幼虫是否分别基于其乳草寄主植物Asclepias syriaca上农药残留的存在和浓度来决定它们的产卵和觅食决策。为此，我们通过实验模拟了六种最常检测到的农药（无论是单独使用还是组合使用）的真实感暴露（一种杀虫剂，两种除草剂和三种杀真菌剂）。这些实验室和温室操作将未经处理的对照与农药的平均浓度或最大浓度配对。最后，我们使用了为期两年的田野调查，将马利筋叶上的农药浓度与君主产卵相关联。
3. 蝴蝶在用混合了六种最大浓度杀虫剂的鸡尾酒处理的乳草上放的鸡蛋减少了，从而导致c。与溶剂对照相比，产卵量减少了30％。新生（第一龄）幼虫在成对盘测定中还显示出对六种化合物中的四种化合物的无农药叶片的偏爱，在平均浓度和最大浓度下均观察到了厌食。后来的幼虫对农药的存在或浓度没有表现出可比的行为反应，但这可能部分归因于所用丙酮溶剂的进料威慑特性。在田间，一种除草剂甲草胺的单株卵载量与叶片浓度的增加呈负相关。尽管所有测试的农药均表现出相似的产卵趋势。
4. 综合与应用。我们的数据提供了证据，表明君主有能力根据宿主植物中存在的农药来适应性地调整其产卵和觅食行为。重要的是，在田间相关的浓度下观察到了这种偏爱，这表明君主通过避免受污染的植物，以行为方式调节其子代的农药暴露风险。在未来的恢复工作中应考虑农药身份和/或栖息地斑块之间/之间的杂草之间的变化，以吸引蝴蝶吸引幼体发育，以及农药与其他植物因素（例如基因型或物种，发育阶段）已知会影响排卵。更广泛地，