Contrasting egg and larval performances help explain polyphagy in a florivorous butterfly

We examined both egg and larval performances in the polyphagous butterfly Parrhasius polibetes (Lycaenidae) using two host plants differing in morphological and ecological traits. Oviposition on mixed and pure patches of Schefflera vinosa (Araliaceae) and Pyrostegia venusta (Bignoniaceae), as well as the fate of eggs laid on both hosts, was assessed. To disentangle the effects of egg origin and host quality on larval performance, eggs were collected from Schefflera and Pyrostegia, and the corresponding newly hatched larvae were reared either on the natal (control) or non-natal (experimental) host. Lastly, we evaluated whether early and late instars are able to switch to alternative hosts. In both mixed and pure patches, parasitism was significantly lower, and oviposition and hatching rates were significantly higher for eggs laid on Schefflera than on Pyrostegia. Survivorship did not differ among treatments. Larvae fed with Pyrostegia were heavier than those fed with Schefflera, regardless of egg origin. Only early instars fed with Schefflera switched to Pyrostegia in the tests; in the remaining cases, larvae fed on the alternative hosts significantly less than on the controls. Our results help to explain why the use of multiple hosts by P. polibetes is maintained in nature, as the host conferring superior egg survival may incur poor larval performance and vice versa. Oviposition pattern is better understood from a tri-trophic rather than a bi-trophic perspective. Our study also highlights the monophagous condition of individual P. polibetes larvae; the constraint for switching to novel hosts is dependent on both larval instar and host plant species.