The role of iridoid glycosides in host-plant specificity of checkerspot butterflies.

The potential role of iridoid glycosides as feeding stimulants forEuphydryas chalcedona larvae was examined in three laboratory experiments. The first experiment examined larval behavior in choice tests between an artificial diet with no additives (AD) and an artificial diet with the iridoid glycoside, catalpol, added (AD + I) in one group; and AD and AD plus a crude extract from which the iridoid glycoside catalpol was crystallized (AD + Ex) in the second group. The larvae were found more often on AD + I or AD + Ex. The second experiment quantified larval consumption of artificial diets when given a choice of AD or AD + I, and AD or AD + Ex, and showed that larvae ate significantly more AD + I or AD + Ex than AD. The third experiment compared growth and survival on six diets: AD; AD + I; artificial diet with dried, ground upScrophularia californica leaves (AD + S); artificial diet with dried, ground upPlantago lanceolata leaves (AD + P);S. californica leaves (S); andP. lanceolata leaves (P). Growth was best onS. californica leaves, and survival was highest onS. californica andP. lanceolata leaves. There were no differences in growth rate or survival between AD andAD + I. Thus, iridoid glycosides serve as feeding attractants and stimulants for larvae ofEuphydryas chalcedona and are suggested as the basis of radiation in butterflies of the genusEuphydryas.