Identification of Novel C₂₀ and C₂₂ Trienoic Acids from Arctiid and Geometrid Female Moths that Produce Polyenyl Type II Sex Pheromone Components

Gas chromatography-mass spectrometry (GC-MS) and GC-electroantennographic detection (EAD) analyses of the sex pheromone extract from a wasp moth, Syntomoides imaon (Lepidoptera: Arctiidae: Syntominae), showed that virgin females produced (Z,Z,Z)-3,6,9-henicosatriene and (Z,Z,Z)-1,3,6,9-henicosatetraene with a trace amount of their C₂₀ analogs. Identification of the chemical structures was facilitated by comparison with authentic standards and the double-bond positions were confirmed by dimethyl disulfide derivatization of monoenes produced by a diimide reduction. In a field test in the Yonaguni-jima Islands, males of the diurnal species were captured in traps baited with a 1:2 mixture of the above-described synthetic C₂₁ polyenes. Lipids were extracted from the abdominal integument and its associated oenocytes and peripheral fat bodies. Following derivatization, fatty acid methyl esters (FAMEs) were fractionated by HPLC equipped with an ODS column, and methyl (Z,Z,Z)-11,14,17-icosatrienoate and (Z,Z,Z)-13,16,19-docosatrienoate were identified by GC-MS. These novel C₂₀ and C₂₂ acid moieties are longer-chain analogs of linolenic acid, (Z,Z,Z)-9,12,15-octadecatrienoic acid. They are presumed to be biosynthetic precursors of the S. imaon pheromone because the C₂₁ trienyl component might be formed by decarboxylation of the C₂₂ acid. On the other hand, the C₂₀ acid, but not the C₂₂ acid, was found in FAMEs of Ascotis selenaria cretacea (Lepidoptera: Geometridae), which secretes C₁₉ pheromone components, (Z,Z,Z)-3,6,9-nonadecatriene and the monoepoxy derivative, indicating that different systems of the chain elongation might play an important role in developing species-specific communication systems mediated with polyunsaturated hydrocarbons and/or epoxy derivatives, components of Type II lepidopteran sex pheromones.