Plant diversity loss can alter higher trophic‐level communities via non‐random species interactions, which in turn may cascade to affect key ecosystem functions. These non‐random linkages might be best captured by patterns of phylogenetic diversity, which take into account co‐evolutionary dependencies. However, lack of adequate phylogenetic data of higher trophic levels hampers our mechanistic understanding of biodiversity relationships in species‐rich ecosystems. We used DNA barcoding to generate data on the phylogenetic diversity of lepidopteran caterpillars in a large‐scale forest biodiversity experiment in subtropical China. We analysed how different metrics of lepidopteran phylogenetic diversity (Faith's PD, MPD, MNTD) and taxonomic diversity were influenced by multiple components of tree diversity (taxonomic, functional, phylogenetic). Our data from six sampling periods represent 7,204 mitochondrial cytochrome c oxidase subunit I (COI) sequences of lepidopteran larvae, clustered into 461 molecular operational taxonomic units. Lepidopteran abundance, the effective number of species (irrespective of the focus on rare or common species) and Faith's PD and MPD (reflecting basal evolutionary splits), but not MNTD (reflecting recent evolutionary splits), significantly increased with experimentally manipulated tree species richness. Lepidopteran MNTD decreased with increasing tree MNTD. Path analyses showed that tree phylogenetic and functional diversity explained part, but not all of the effects of tree species richness on lepidopteran diversity. Importantly, tree diversity effects on lepidopteran diversity were to a large extent indirect, operating via changes in lepidopteran abundance. Synthesis. Our study shows that evolutionary dependencies determine the response of herbivore communities to changes in host plant diversity. Incorporating a wider range of diversity metrics both at the level of producers and consumers can thus help to develop a more comprehensive understanding of the functional consequences of biodiversity change across trophic levels. Moreover, the dependence of trophic linkages on herbivore abundances underlines the need to address the consequences of current declines in insect abundances for ecosystem structure and functioning. Foreign Language 
摘要 植物多样性能通过种间相互作用对更高营养级的种群结构产生效应, 而重要的生态系统功能也可能由此受到影响。这些非随机的级联效应可能较好的被系统发育多样性解释, 因为后者包含了物种协同进化的特性。然而, 对高营养级的系统发育多样性仍然缺乏足够的研究, 这限制了我们对物种丰富的生态系统中生物多样性关系的内在机制的理解。 我们在中国亚热带的 BEF‐China 大型生物多样性实验基地以鳞翅目幼虫为研究对象, 基于 DNA 条形码计算了鳞翅目幼虫的系统发育多样性指数 (PD, MPD, MNTD）, 并结合了鳞翅目幼虫的物种丰富度分析了其是否受到树种的不同的多样性指数 （物种丰富度、功能多样性和系统发育多样性） 的影响。 采样集中于 2017 和 2018 年的 4 月、 6 月和 9 月。基于 6 次采集所得的鳞翅目幼虫样本，最终获取了 7204 条 COI 序列， 分成 461 个可操纵分类单元。研究发现鳞翅目幼虫多度、有效物种数、 PD 和 MPD 均与树种多样性呈正相关（鳞翅目幼虫 MNTD 除外）。但鳞翅目幼虫 MNTD 随着树 MNTD 的增加而显著降低。结构方程模型的分析结果显示了树的系统发育多样性和功能多样性能够部分解释树种多样性对鳞翅目幼虫多样性的效应。重要的是， 树种多样性能够很大程度上通过鳞翅目幼虫的多度间接地影响其多样性指数。 综上，我们的研究结果表明：系统发育关系在一定程度上决定了寄主植物群落的改变对植食者群落产生的影响。因此， 在生产者和消费者两个营养级中纳入更广泛的多样性指标可以帮助我们更全面地理解由不同营养级的生物多样性变化而产生一系列生态学效应。与此同时， 营养级关系对植食者丰富度的依赖表明了我们应该关注昆虫数量下降对生态系统结构和功能所产生的一系列影响。 We integrated multiple components of plant and herbivore diversity to unravel the linkages that drive biodiversity relationships and determine the consequences of biodiversity loss across trophic levels. Our study suggests that lepidopteran phylogenetic diversity is significantly affected by plant species loss when basic splits in the evolutionary history are considered. Moreover, we show that multiple components of tree diversity can synergistically affect species richness and phylogenetic diversity of lepidopteran larvae. Importantly, plant diversity effects were indirectly mediated by herbivore abundance – which sheds light on the consequences of recently observed declines in the number of insects for the structuring and functioning of ecosystems, including evolutionary dependencies between plants and their herbivore communities.