Pyrrolizidine ester alkaloid in danaid butterflies

Abstract

THE dihydropyrrolizines (I–III, Fig. 1a) found in the hairpencil secretions of male butterflies of the sub-family Danainae^1–5 and shown in one instance to be an important courtship pheromone⁶, are closely related to the hepatotoxic dihydropyrrolizine metabolites of the pyrrolizidine alkaloids^7,8. We have previously adduced evidence which points strongly to these hairpencil constituents having their origin in plant alkaloids (or their metabolites) ingested by the adult insects⁵. Thus, there are a number of reports of adult male danaid butterflies being strongly attracted to, and sometimes feeding on, dead and withering plants containing pyrrolizidine alkaloids⁵. With one species, Danaus chrysippus petilea (Stoll) we have shown⁵ that when dihydropyrrolizine-deficient laboratory-reared butterflies are given access to one such alkaloid containing plant, Heliotropium amplexicaule (Vahl), they soon acquire the dihydropyrrolizine ketone (I) which is normally found on the hairpencils of this species.