Grasses accumulate large amounts of silicon (Si) which acts as a highly effective physical defence against insect herbivory, however recent evidence shows that Si supplementation also modifies plant secondary metabolite concetrations. Changes in plant secondary metabolites concentrations can have cascading effects on higher trophic levels, such as parasitoids, as they are dependent on the host herbivore for growth and development. However, relatively little is known about how Si application affects higher trophic levels. We examined the effects of Si addition on alkaloid content in leaves of Phalaris aquatica (Poaceae) and the effect on interactions between an aphid (Rhopalosiphum padi) and its parasitoid (Aphidius colemani). Si supplementation had no effect on aphid abundance or parasitism rate. Adult aphids, aphid mummies (parasitised aphids) and the emergent parasitoids were, however, significantly smaller on Si+ plants. Parasitoid traits (size and emergence) were correlated with aphid mummy size. Si addition reduced parasitoid emergence rate and size due to reduced host mummy size, in addition, significantly fewer females emerged from mummies on Si+ plants. Aphid infestation significantly altered alkaloids concentrations, reducing gramine by 80% while increasing tryptamine by 91% in Si− plants. Si addition reduced aphid-induced tryptamine concentrations by 64% and increased 5-MeO-tryptamine by over 800% in control and 142% in aphid infested plants. Our results show that while Si addition has modest impacts on the herbivore, it significantly alters secondary metabolites and has stronger effects on the higher trophic level through changes in the quality of the parasitised host.

草中积累了大量的硅（Si），对昆虫的食草性具有高度有效的物理防御作用，但是最近的证据表明，硅的添加还改变了植物次生代谢产物的含量。植物次生代谢产物浓度的变化可对较高营养水平（如拟寄生物）产生级联效应，因为它们依赖于宿主草食动物的生长和发育。然而，对于硅的应用如何影响更高的营养水平知之甚少。我们研究了添加硅对Ph草（Poaceae）叶片中生物碱含量的影响，以及对蚜虫（Rhodolosiphum padi）和其寄生蜂（Aphidius colemani）之间相互作用的影响。）。硅的添加对蚜虫的丰度或寄生率没有影响。然而，在Si +植物上，成年蚜虫，蚜虫木乃伊（被寄生的蚜虫）和出苗的拟寄生虫明显较小。寄生性状（大小和出苗）与蚜虫木乃伊大小相关。硅的添加由于寄主木乃伊大小的减小而降低了寄生虫的出现率和大小，此外，Si +植物的木乃伊中出现的雌性显着减少。蚜虫侵染显着改变了生物碱的浓度，在Si-植物中降低了80％的草胺，而将色胺提高了91％。硅的添加使蚜虫诱导的色胺浓度降低了64％，而5-MeO-色胺的控制量增加了800％，蚜虫侵染的植物中的含量增加了142％。我们的结果表明，尽管添加Si对草食动物影响不大，