Male sex pheromone of a giant danaine butterfly, Idea leuconoe

Males of a giant danaine butterfly, Idea leuconoe, display hairpencils during courtship. The females were visually attracted to and olfactorily arrested by an artificial butterfly model to which male hairpencil extracts were added. The hairpencil extracts contained a complex mixture of volatiles, including pyrrolizidine alkaloid (PA) derivatives (danaidone, viridifloric beta-lactone), aromatics (phenol, p-cresol, benzoic acid), terpenoids (geranyl methyl thioether, (E,E)-farnesol), a series of gamma-lactones (6-hydroxy-4-undecanolides and its homologs), hydrocarbons [(Z)-9-tricosene, etc.], and several compounds with higher molecular weight. A mixture of the major volatiles applied to a butterfly dummy strongly elicited an abdomen-curling acceptance posture in females. Viridifloric beta-lactone and danaidone induced significant electroantennogram responses on the female's antennae, suggesting their principal role together with other hairpencil components as a sex pheromone to seduce females. I. leuconoe males seem to acquire the precursor for both of the PA fragments from the host plant, Parsonsia laevigata (Apocynaceae), during the larval stage; thereby they do not show pharmacophagous behavior towards PA-containing plants during the adult stage. However, males are pharmacophagously attracted to and feed on a number of simple phenolic compounds in a manner similar to other danaine species towards PAs. Wild males sequester one of the phagostimulants, (-)-mellein, in the hairpencils in varying quantities. Phenolic compounds incorporated in the hairpencils may act primarily as warning odors linked with the defensive PAs present in the body tissues.