Specific mixtures of secretions from male scent organs of African milkweed butterflies (Danainae)

Abstract

The abdominal androconial organs (hairpencils: male scent glands) of samples of ten African milkweed butterfly species (Lepidoptera: Danainae) belonging to Danaus, Tirumala and Amauris , including all nine species commonly encountered in Kenya, have been analysed by gas chromatography and mass spectrometry. A total of 214 compounds have been identified, belonging to 14 chemical classes: hydrocarbons, alcohols, aldehydes, ketones, esters, lactones, carboxylic acids, oxidized carboxylic acids, aromatics, derivatives of pyrrolizidine alkaloids (PAs), monoterpenes, sesquiterpenes, other terpenoids and tetrahydrofurans. Various compounds only rarely or never found in insects before, including some previously unknown in nature, are present in the hairpencils. Excluding the numerous tetrahydrofurans, which were not investigated systematically, the number of compounds ranges from 12-59 per species. All ten species have distinct mixtures of volatiles, including, in all cases, species-specific compounds (autapomorphies). In addition, the co-occurrence of compounds between species (synapomorphies) exhibits a strongly hierarchical chemo-taxonomic pattern which has been demonstrated to be largely consistent with a previous cladistic analysis based on adult morphology. The potential significance of these findings in relation to chemical communication and speciation in these mimetic butterflies is discussed.