Incorporation of an introduced weed into the diet of a native butterfly: consequences for preference, performance and chemical defense.

The introduction of exotic plants, animals, and pathogens into non-native ecosystems can have profound effects on native organisms. Plantago lanceolata, narrow-leaf or ribwort plantain (Plantaginaceae), is a weed that was introduced to North America from Eurasia approximately 200 years ago and that has been incorporated into the diet of a variety of native North American herbivores. Plantain contains two iridoid glycosides, aucubin and catalpol, that can be toxic or deterrent to non-specialized herbivores or herbivores that have recently incorporated this species into their diet. Anartia jatrophae (Nymphalidae), the white peacock, feeds on plants in five families including the Plantaginaceae, and was recently observed feeding on plantain; however, the effects of feeding on this novel host plant are unknown. In this study, we performed a series of experiments to assess larval preference and performance on the introduced P. lanceolata and on a native host plant that does not contain iridoid glycosides, water hyssop, Bacopa monnieri (Plantaginaceae). We also tested whether or not white peacocks were able to sequester iridoid glycosides and compared this ability with an iridoid specialist, the buckeye, Junonia coenia (Nymphalidae). White peacocks successfully developed to the adult stage on plantain; larvae grew more slowly but pupae were heavier when compared with larvae and pupae reared on the native host plant. Larvae showed induced feeding preferences for the host plant on which they were reared. Furthermore, larvae sequestered small amounts of iridoids that were also retained in pupae and adults. These results suggest that incorporation of the introduced weed, plantain, into the diet of the white peacock may have important consequences for larval performance and preference, as well as for interactions with natural enemies.