Some plants are able to accumulate on their leaves metals taken from the soil, using this as a defence against herbivorous arthropods. However, herbivore response to metal accumulation in plants is known to be variable. While some species and taxonomic groups are less affected than others, hormetic effects have also been observed in spider mites, herbivorous crop pests. Still, knowledge on the range and causes of intraspecific variation in the response of herbivores to metal accumulation is lacking. Here, using two species of spider mites, Tetranychus urticae and Tetranychus evansi, we tested the variation in 17 populations in response to cadmium-accumulating tomato plants and the drivers of such variation. We observed a nonlinear, hormetic response of mites to plants with cadmium in some, but not all, populations. The same pattern was recaptured in artificial diets with different concentrations of cadmium but not in artificial diets with sugars, which change in the plant in response to cadmium. This indicates that herbivores on metal-accumulating plants respond to metals, not to the variations in leaf carbohydrates. Therefore, metals exert different effects on herbivores according to the amount accumulated, but independently of other studied plant traits. This knowledge is key to the understanding of the mechanisms underlying herbivore responses to metal-based plant defences and to pesticides containing heavy metals. Additionally, our findings draw attention to the need of considering intraspecific variation and nonlinearities when studying the effects of metals and other contaminants on herbivorous arthropods.

一些植物能够在叶子上积累从土壤中提取的金属，以此作为对食草节肢动物的防御。然而，已知食草动物对植物中金属积累的反应是可变的。虽然一些物种和分类群受到的影响比其他物种和分类群少，但在蜘蛛螨、草食性作物害虫中也观察到了毒物效应。尽管如此，关于食草动物对金属积累反应的种内变异的范围和原因的知识仍然缺乏。在这里，使用两种蜘蛛螨，Tetranychus urticae和Tetranychus evansi，我们测试了 17 个种群对镉积累番茄植物的反应以及这种变化的驱动因素。我们观察到螨虫在一些（但不是全部）种群中对含镉植物的非线性、促激反应。在含有不同浓度镉的人工日粮中重新捕获了相同的模式，但在含有糖的人工日粮中却没有，因为糖在植物中响应镉而发生变化。这表明金属积累植物上的食草动物对金属有反应，而不是对叶子碳水化合物的变化有反应。因此，金属根据积累的量对食草动物产生不同的影响，但与其他研究的植物性状无关。这些知识对于理解草食动物对基于金属的植物防御和含有重金属的杀虫剂的反应机制至关重要。