Global environmental changes such as increased temperatures and deposition of nutrients are greatly affecting many organisms, including a number of Lepidoptera species. Numerous studies have been conducted to determine the impacts of temperature and nutrients on herbivores, although many have tested each variable separately and could consequently be missing possible interactive effects. In this experiment, we tested the interactive effects of nutrients and temperature on interactions between Pieris rapae and its host plant, Brassica oleracea. Using a full-factorial design, we grew Brussels sprouts at one of three temperatures (16±2°C, 23±2°C, or 30±2°C), on one of three nutrient treatments that varied in the ratio of nitrogen to phosphorus (4:1, 16:1, or 64:1). One first instar caterpillar was assigned to each plant at the various treatments and was fed experimental leaves until pupation. We measured macronutrient and elemental content of leaves for each plant, as well as various life history traits for larvae, including time to pupation, amount of leaves eaten, adult mass, and adult lipid content. Plant macronutrient content was not affected by temperature treatment, but was significantly affected by nutrient treatment. We found an interactive effect for only one variable - time to pupation - with the majority of other significant variables being influenced by temperature, such as time to pupation, survival, and adult size. We also found adult lipid content to be highly affected by nutrient treatment, with butterflies from the warmest treatment having a higher lipid content. Our results suggest that temperature may be the most influential variable for herbivore growth and fitness.