1. The relationship between plant diversity and ecosystems functions such as regulation of insect herbivory is complex and context-dependent. The empirical data necessary to account for these interactions are scarce.
2. Our objective is to test the top-down effects of predation and bottom-up effects of plant traits to understand what drives patterns of herbivory in managed systems.
3. We established single- and multiple-variety willow field plots with up to four varieties, to study herbivory and predation, and greenhouse experiments to investigate the effects on insect preference and performance.
4. Herbivore damage in the field was higher in single- as opposed to multiple-variety plots for the two most prevalent insect types in one of the 3 years. Predation was higher in multiple-variety plots than in pure plots during 2016 but the opposite occurred in 2018. Predation on leaf beetle eggs was higher in multiple-variety plots, but the result was related to specific variety mixtures rather than increased numbers of varieties. Leaf beetle feeding choice and egg-laying were influenced to some extent by plant diversity.
5. Our results give insights into the links between plant diversity, composition and levels of herbivore damage. They also spark questions about how temporal aspects influence these links.

中文翻译：

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柳树多样性对昆虫食草和捕食的影响

1. 植物多样性与生态系统功能（如昆虫食草的调节）之间的关系是复杂的且取决于环境。解释这些相互作用所需的经验数据很少。
2. 我们的目标是测试捕食的自上而下效应和植物性状自下而上的效应，以了解是什么驱动了管理系统中的食草动物模式。
3. 我们建立了多达四个品种的单品种和多品种柳树田地，以研究食草和捕食，以及温室实验以研究对昆虫偏好和性能的影响。
4. 在三年中的一年中，两种最流行的昆虫类型在田间的草食动物损害在单一地块中高于多品种地块。2016 年多品种地块的捕食率高于纯地块，但 2018 年的情况相反。多品种地块对叶甲虫卵的捕食率较高，但结果与特定品种混合而不是品种数量增加有关。叶甲虫的取食选择和产卵在一定程度上受植物多样性的影响。
5. 我们的研究结果深入了解了植物多样性、组成和食草动物损害程度之间的联系。它们还引发了关于时间方面如何影响这些联系的问题。