Biosynthesis of a volatile, methly-branched hydrocarbon sex pheromone from leucine by arctiid moths (Holomelina spp.)

The biosythesis of 2‐methylheptadecane was investigated in three moth species, Holomelina lamae, H. immaculata, and H. aurantiaca, all of which use this hydrocarbon as the principal component of their volatile sex pheromone. Following injection into adult females, deuterium‐labeled leucine and isovaleric acid were readily incorporated into pheromone but valine and isobutyric acids were not. Radiolabeled acetate and malonic acid also gave good incorporation into pheromone as did 13‐methyltetradecanoic acid and 15‐methlhexadecanoic acid. These findings support a biosynthesis pathway whereby leucine is converted to isovaleric acid, which serves as the methly branch donor and chain initiator; malonic acid donates seven additional 2 carbon units to from 17‐methloctadecanoic acid, which is then deccarboxylated to produce the odd‐carbon chain hydrocarbon pheromone. Methyl‐branched fatty acids were detected in only small amounts or were absent in pheromone gland extracts, and among the different glandular lipid classes, labeled leucine and acetate were only incorporated into hydrocarbons. These findings suggest that onceinitiated, biosynthesis of the pheromone proceeds rapidly with little or no accu mulation of intermediates and/or that the pheromone or some long‐chain intermediate is biosynthesized elsewhere in the insect and transported to the gland.