Evidence for de novo biosynthesis of osmeterial secretions in young larvae of the swallowtail butterflies (Papilio): deuterium incorporation in vivo into sesquiterpene hydrocarbons as revealed by mass spectrometry

Abstract

Investigations were carried out on the origin of osmeterial secretions exuded by fourth instar larvae of Papilio helenus and P. protenor that had been reported to secrete a variety of terpenic compounds. Variations in the chemical composition of the secretion induced by dietary and/or genetic factors were quantitative rather than qualitative in both species. Overall pattern of the chemical constituents was found to be highly species-specific and substantially invariable in a given species. Several sesquiterpene hydrocarbons secreted by the larvae were not present in detectable amounts in the leaves of the host plant, Fagara ailantoides, suggesting that the sesquiterpenes were biosynthesized by these larvae. Deuterium was efficiently incorporated in vivo into sesquiterpene hydrocarbons in the secretion, (E)-β−farnesene, β−caryophyllene, germacrene-A and germacrene-B, by topical application of deuteriumlabelled acetic acid to everted osmeteria, while similar treatment with deuterium oxide resulted in much lower incorporation of deuterium. These results provide evidence for de nova biosynthesis of sesquiterpene hydrocarbons in young Papilio larvae.