This dissertation is composed of three manuscripts that describe aspects of the interactions between the Chalcedon Checkerspot Butterfly, Euphydryas chalcedona (Dbldy. and Hew.) (Lepidoptera, Nymphalidae) and its larval host plants on the Stanford University Jasper Ridge Biological Preserve in San Mateo County, California. At Jasper Ridge, the larvae regularly feed on two species of Scrophulariaceae, Diplacus aurantiacus and Scrophularia californica. Diplacus is a drought-deciduous shrub that carries green, terminal leaves throughout the year. Scrophularia is an herbaceous perennial that dies back to ground level by August with the annual summer drought and reinitiates growth when winter rains occur. Diplacus plants produce a defensive chemical, a phenolic leaf-surface resin; Scrophularia has no prominent defensive chemical. Studies conducted in the laboratory and on Jasper Ridge attempted to compare the utilization of plants that differ in growth and nutritional qualities. The first Study related larval feeding behavior to leaf nitrogen and resin contents of Diplacus and to leaf nitrogen content of Scrophularia. Euphydryas chalcedona larvae consume substantial amounts of the leaf surface area on both plants (often over 75%), however the location of feeding activity differs between plant species. Resin production is highest on young and old leaves and larvae feed selectively on newly-expanded Diplacus leaves which produce less resin (by leaf dry weight). Larvae preferred those Diplacus leaves with the highest nitrogen: resin ratio in controlled choice tests. Scrophularia leaves showed no significant differences in leaf nitrogen content and larvae fed relatively evenly among all Scrophularia leaves. These results demonstrate the spectrum of resources, within plants, that are encountered by herbivores and the capacity of herbivores to selectively feed on the apparently more nutritious food. The second study involved a set of feeding experiments that were designed to differentiate the effects of individual larval feeding experience or maternal food type on the growth and digestive efficiency of young larvae. These feeding studies showed that Scrophularia was significantly more nutritious than Diplacus in terms of growth and standard digestibility parameters. Larval food type had a significant effect on larval performance and there were no obvious genetically-mediated effects on food utilization. In choice tests, larvae consumed significantly more Scrophularia than Diplacus, regardless of their previous feeding experience. The third study examined oviposition behavior of adult Euphydryas chalcedona in relation to the nutritional qualities of Diplacus and Scrophularia and to larval food preferences. Butterflies were allowed to land on, and examine, both plants in the greenhouse, insectary, and on Jasper Ridge. Their behavior was monitored and acceptance of hosts was noted. All females, regardless of their host-origin, accepted Scrophularia more frequently ...