Host plant consumption and pathogen infection commonly influence insect traits related to development and immunity, which are ultimately reflected in the behavior and physiology of the insect. Herein, we explored changes in the metabolome of a generalist insect herbivore, Vanessa cardui (Lepidoptera: Nymphalidae), in response to both dietary variation and pathogen infection in order to gain insight into tritrophic interactions for insect metabolism and immunity. Caterpillars were reared on two different host plants, Plantago lanceolata (Plantaginaceae) and Taraxacum officinale (Asteraceae) and subjected to a viral infection by Junonia coenia densovirus (JcDV), along with assays to determine the insect immune response and development. Richness and diversity of plant and caterpillar metabolites were evaluated using a liquid chromatography-mass spectrometry approach and showed that viral infection induced changes to the chemical content of V. cardui hemolymph and frass dependent upon host plant consumption. Overall, the immune response as measured by phenoloxidase (PO) enzymatic activity was higher in individuals feeding on P. lanceolata compared with those feeding on T. officinale. Additionally, infection with JcDV caused suppression of PO activity, which was not host plant dependent. We conclude that viral infection combined with host plant consumption creates a unique chemical environment, particularly within the insect hemolymph. Whether and how these metabolites contribute to defense against viral infection is an open question in chemical ecology.

寄主植物的消耗和病原体感染通常会影响与发育和免疫相关的昆虫性状，这些性状最终反映在昆虫的行为和生理上。在此，我们探索了通才昆虫草食动物Vanessa cardui （鳞翅目：蛱蝶科）的代谢组变化，以响应饮食变化和病原体感染，以深入了解昆虫代谢和免疫的三营养相互作用。毛虫在两种不同的宿主植物——车前草（车前草科）和蒲公英（菊科）上饲养，并受到 Junonia coenia densovirus (JcDV) 的病毒感染，并进行测定以确定昆虫免疫反应和发育。使用液相色谱-质谱法评估了植物和毛毛虫代谢物的丰富度和多样性，结果表明，病毒感染会根据宿主植物的消耗诱导卡杜伊菌血淋巴和粪便化学含量的变化。总体而言，通过酚氧化酶 (PO) 酶活性测量，以P. lanceolata为食的个体的免疫反应高于以T. officinale为食的个体。此外，JcDV 感染导致 PO 活性受到抑制，这不依赖于宿主植物。我们得出的结论是，病毒感染与宿主植物消耗相结合创造了独特的化学环境，特别是在昆虫血淋巴内。这些代谢物是否以及如何有助于防御病毒感染是化学生态学中的一个悬而未决的问题。