Appraisal of the acceptability of subtropical rutaceous plants for a swallowtail butterfly, Papilio protenor demetrius (Lepidoptera: Papilionidae)

Abstract

A Rutaceae-feeding swallowtail butterfly, Papilio protenor demetrius, exploits only a few plant species as hosts in the field. We examined in detail the acceptability of five potential rutaceous hosts occurring in the subtropics for ovipositing females of a Hiroshima population of the butterfly. The plants tested were Citrus depressa, Toddalia asiatica, Evodia meliifolia, Melicope triphylla, and Murraya paniculata, which are distributed mainly in the Southwestern Islands of Japan, thus in allopatry with the butterfly. Female responses to the foliage, methanol extracts and partitioned fractions from these plants were assayed for the presence of oviposition stimulants and/or deterrents. The foliage of C. depressa and T. asiatica strongly stimulated egg-laying, whereas ovipositing females only marginally accepted E. meliifolia and Me. triphylla, and virtually rejected Mu. paniculata. Further experiments with methanol extracts and fractions derived from the respective plants revealed that both C. depressa and T. asiatica contained potent oviposition stimulant(s) particularly in the aqueous fractions, and that the aqueous fractions of E. meliifolia and Mu. paniculata, despite their poor or little acceptability, contained moderate and weak stimulant(s), respectively. However, certain volatile deterrent(s) seemed to be responsible for the rejection of Mu. paniculata by females. Me. triphylla appeared to have neither appreciable stimulant(s) nor deterrent(s). Larval survival on these plants was also recorded as an estimate of fitness. Larvae performed very well on C. depressa. Unexpectedly, however, larvae did not survive on T. asiatica at all, but successfully grew on E. meliifolia. Larvae altogether failed to grow on both Me. triphylla and Mu. paniculata, suggesting the involvement of antifeedant(s) and/or toxic substance(s) in those plants to which larvae were maladapted.