Chapter 1. Previous studies which attempted to determine the role of food resources in the population structure of butterflies concentrated on larval host plant dynamics. Adult resources were thought important as components of habitat suitability but their exact role had not been ascertained. In a habitat with an uncommon spacial arrangement of larval and adult resources, adult Euphydras chalcedona were found more often near a single nectar concentration in otherwise broadly suitable habitat. The distribution of offspring correlated with the distribution of nectar sources indicating that adult resources are a primary determinant of habitat selection. Chapter 2. The role of adult feeding in butterfly reproduction was determined more precisely. Carbohydrate intake was key in maximizing female longevity, body weight maintenance and egg production in Euphydryas editha. Amino acids played a role enhancing individual egg weight, increasing the chance of offspring survival. Females fed artificial nectar had about 60% greater egg production than females not fed. However it is likely that under most circumstances on Jasper Ridge and in similar habitats this does not result in commensurate increases in surviving offspring. Adult feeding increases the size of later egg masses. During years of normal and below normal precipitation larvae emerging from later egg masses cannot reach obligatory size for diapause because they do not find adequate food. Where mortality is density-independent, the role played by nectar is in enhancing egg production during years of high rainfall when later egg masses contribute to surviving larvae. Such infrequent population increases are important in maintaining a large population size, reducing the chances of extinction during inevitable drought years. Chapter 3. Euphydryas editha adults exhibited strong preferences for specific nectar sources which (1) vary between habitats and (2) change through the season. Males and females exhibited similar preferences, though the length of individual foraging bouts differed. E. editha was surprisingly constant in visitation to specific sources. Though efficient foragers the butterflies probably are inefficient pollinators. The proportion of pollen carried reflected source abundance rather than the pattern of visitation to the sources. Nectar source use was a function of the volume of nectar available per plant and its physical accessibility to the foraging butterfly.