Temperature and photoperiod generate seasonal polyphenism in butterfly wing shape and pattern,
providing evidence that environmental factors affect wing pattern expression during the pupal stage.
However, little data exist regarding the importance of host plant secondary metabolites to which
butterflies are exposed in the larval stage to such differences. We had three aims for this experiment: 1)
to determine if exposure of larvae to anti-herbivore chemicals alters wing pattern or color, 2) to
determine how different classes of chemicals affect butterfly wing patterns, and 3) to determine if
chemicals affect the wings of different species in similar ways. We raised Painted Lady (Vanessa cardui)
and Common Buckeye (Junonia coenia) larvae on different diets, including field collected host plants
(Plantago major and P. lanceolata) and artificial diets amended with chemicals (oleanolic acid and
catalpol) found in those host plants. We reared larvae on artificial diet until the 3rd instar, fed them on
experimental treatments until pupation, reared them through to pupation, and measured colors,
eyespot sizes, and other wing patterns elements using ImageJ.
Results/Conclusions
Vanessa cardui raised on host plants had smaller wings and relatively smaller eyespot elements from V.
cardui larvae raised on artificial diet, regardless of the chemicals added to artificial diet. Junonia coenia
larvae reared on P. lanceolata had greater amounts of blue iridescent scales on the dorsal forewings
compared to those reared on P. major. Moreover, female J. coenia had larger hindwings when raised on
P. lanceolata. This study is the first to demonstrate that host plants can create phenotypic
variation in structural color and one of the first to document larval host plant effects on eyespot size and
pigments expressed in the adult stage. Although diets amended with chemicals did not produce
variation in wing patterns in this study, consistent differences in wing patterns across individuals of both
species raised on different host plants suggests a role for plant metabolites in phenotypic wing pattern
variation.