The introduction of novel host plants into new habitats may have profound effects on native organisms and their interactions with other trophic levels; these effects may vary from negative to neutral to positive. Here we report data from three lepidopteran species in the family Nymphalidae that have incorporated the novel host plant, Plantago lanceolata (Plantaginaceae) (narrow-leaved plantain) into their diet: Anartia jatrophe (the White Peacock), Vanessa cardui (the Painted Lady), and Euphydryas phaeton (the Baltimore checkerspot). We used a combination of field collections, chemical analysis via gas chromatography, and laboratory experiments to ask how use of this novel host plant affects chemical defense, immune response, and susceptibility to a virus.
Our data showed that: 1) A. jatrophe and V. cardui were able to sequester defense compounds (iridoid glycosides) from the novel host plant that are not available from their native hosts, although their ability to do so varied between these species; 2) feeding on P. lanceolata also affected growth and immune response of these two species; 3) feeding on P. lanceolata altered chemical defense in E. phaeton compared to the native host plant; and 4) use of P. lanceolata also reduced E. phaeton caterpillar immune response and increased susceptibility to a virus. These results indicate the effects of incorporation of novel host plants may not always be negative, and that consideration of higher trophic levels is of particular importance.