Abstract: Climatic warming affects plant growth and physiology, yet how warming alters chemistry in invasive plants and indirectly affects herbivorous insects remains largely unknown. Here, we explored warming-induced changes in leaf chemistry of the invasive plant Alternanthera philoxeroides and its native congener Alternanthera sessilis, and further examined how these changes affected the performance of the herbivores, Cassida piperata and Spodoptera litura. We conducted a simulated warming experiment to address its effects on 13 leaf chemical traits of A. philoxeroides and A. sessilis. We measured growth and development time of two herbivores reared on plants from warming or ambient controls. Warming significantly affected leaf chemistry composition for both the invasive and native Alternanthera. Warming decreased nitrogen concentration in A. philoxeroides and increased total flavonoid and total phenol concentration in A. sessilis. The effects of warming on nutrients (i.e. fructose, sucrose, total soluble sugar and starch) varied with individual chemicals and plant species. Weight of C. piperata pupal and S. litura larval reared on warming-treated A. sessilis significantly decreased compared with non-warmed control, and a similar pattern was observed for weight of S. litura larval feeding on warming-treated A. philoxeroides. In addition, warming-treated A. sessilis significantly prolonged larval development time of S. litura. These results indicate that warming can directly affect the leaf chemistry in both invasive plant and its native congener, but these effects vary by species. Such differences in warming-induced changes in plant chemistry could indirectly affect herbivorous insects associated with the invasive and native plants.

Key words: climate warming, direct and indirect effects, invasive plant, herbivore, secondary chemicals