The coevolution of Euphydryas chalcedona butterflies and their larval host plants

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Abstract
Oviposition host preference of the checkerspot butterfly, Euphydryas chalcedona, was examined in relation to the nutritional qualities of two regularly-used larval host plants. In many coastal-California colonies, E. chalcedona larvae feed primarily on a common drought-deciduous shrub, Diplacus aurantiacus, but also use an herbaceous perennial, Scrophularia californica. Diplacus has been shown to be nutritionally inferior to Scrophularia, however, Diplacus may be a more persistant resource in ecological and evolutionary time. In both greenhouse and field trials, butterflies strongly preferred to oviposit on Scrophularia, but would oviposit on Diplacus if Scrophularia was not available. Host preference of adults was not related to their larval feeding experience. In trials testing the effects of sun and shade on oviposition behavior, E. chalcedona preferred to oviposit on hosts in sun. Scrophularia often occurs in shadier habitats than Diplacus and Scrophularia plants placed in shade were accepted more often than Diplacus plants placed in the shade. Host use by E. chalcedona butterflies appears to reflect a trade-off between nutritional quality and resource relability.