Light and temperature are ecological factors that are known to influence leaf quality and herbivory. Because temperature is likely to vary with light environment, the effects that each factor has on herbivore performance and seasonal herbivory rates are likely to be confounded. We studied how light and thermal environment influenced consumption and conversion of Lindera benzoin L. (Lauraceae) leaf material by Epimecis hortaria F. (Lepidoptera: Geometridae) in field and laboratory settings. Ambient and leaf surface temperatures were higher in the sun than in the shade. Experimental enclosures increased feeding temperatures by <1°C. Larvae of E. hortaria feeding at warmer temperatures consumed more leaf material than their counterparts in cooler conditions in the laboratory. However, in the field, herbivores tended to remove less leaf material from plants in warm, sunlit habitats where seasonal herbivory is lower. Conversion of leaf area eaten into biomass was higher in larvae feeding on L. benzoin leaves from sun habitats for all field and laboratory treatments and was independent of temperature, suggesting that sun leaves are more nutritious for E. hortaria than shade leaves. While elevations in ambient temperature play a significant role in laboratory-based settings, the effects of ambient temperature on herbivory rates in the natural environment seem to be muted by differences in leaf quality and antiherbivore defenses in sun and shade populations of L. benzoin.