Ecological adaptation of an Aristolochiaceae-feeding swallowtail butterfly,Atrophaneura alcinous, to aristolochic acids

Seven analogs of aristolochic acids (I, II, III, B, C, D, and E) were isolated from the leaves ofAristolochia debilis and characterized as the larval feeding stimulants of an Aristolochiaceae-feeding swallowtail butterfly,Atrophaneura alcinous. Aristolochic acids showed synergistic activity in combination with the water-soluble components in the leaf extract. Aristolochic acids were detected in the body tissues and specialized organs throughout all life stages ofA. alcinous. Larval osmeterial fluid contained aristolochic acids as high as 2% of the secretions, the compositions of which were similar to that found in the leaf extracts. In contrast, the eggs selectively contained aristolochic acids I and II. These two acids were present both in the egg yolk and egg coating material as well as in the collateral glands (glandulae sebaceae) of the adult females. The cannibalistic activity of the larvae against the eggs and pupae seemed to be triggered by aristolochic acids present on the egg surface and pupal cuticle, suggesting a possible adaptive mechanism in this species. Aristolocic acid I deterred feeding of tree sparrows, which suggested a defensive role against vertebrate predators.