Euphydryas chalcedona prediapause larvae were reared on fertilized and control shrubs of the host plant, Diplacus aurantiacus. Larval growth was enhanced by high leaf nitrogen content and inhibited by high leaf phenolic resin content. Larvae fed less on leaves near the branch tip which contained a higher leaf resin content. The results agree with prior laboratory investigation that the dietary content of nitrogen and D. aurantiacus leaf resin are major determinants of E. chalcedona larval growth and suggest that the phenolic leaf resin of Diplacus may both deter and inhibit leaf herbivores.