Date Published: April 23, 2019
Publisher: Public Library of Science
Author(s): Heidy Herrera, Wilson Barros-Parada, Jan Bergmann, J Joe Hull.
The main pheromone compound of Chilecomadia valdiviana (Lepidoptera: Cossidae) has been recently identified as (7Z,10Z)-7,10-hexadecadienal. The biosynthesis of this pheromone compound showing attributes of both Type I and Type II lepidopteran pheromones was studied by the topical application of isotope-labeled fatty acids to the pheromone gland and subsequent analysis of the gland contents (pheromone compounds and fatty acyl compounds) by gas chromatography-mass spectrometry. The deuterium label of D11-linoleic acid was incorporated into the pheromone compound and its putative acyl precursor (7Z,10Z)-7,10-hexadecadienoate, demonstrating that the pheromone compound is biosynthesized from linoleic acid by chain-shortening and further functional group transformation. Furthermore, the deuterium label of D3-stearic acid was also incorporated into the pheromone compound, which indicates that the pheromone can be synthesized de novo by C. valdiviana, as is the case for Type I lepidopteran pheromone compounds.
The sex pheromones of about 600 species of Lepidoptera have been identified [1,2] and according to their structure, they are often classified as “Type I” or “Type II” pheromones. The common feature of Type I pheromones, produced by the majority of species, is an unbranched chain of 10–18 carbon atoms possessing a terminal oxygenated functional group (alcohol, aldehyde, or acetate) and 0–3 double bonds along the chain, while Type II pheromones, produced by a number of species in the families Arctiidae, Geometridae, Lymantriidae, and Noctuidae, are straight-chain, polyunsaturated hydrocarbons and their epoxy derivatives [1,3].
The in vivo experiments carried out in this study confirmed the transformation of deuterium-labeled linoleic acid to deuterium-labeled Z7,Z10-16:Ald in the pheromone gland of C. valdiviana females. The first step in this transformation is the chain-shortening of linoleic acid by two carbons, as was evidenced by the appearance of deuterium-labeled Z7,Z10-16:COOMe among the fatty acyl compounds in the pheromone gland after treatment with D11-linoleic acid. This fatty acyl precursor is then further transformed to Z7,Z10-16:Ald, presumably by reduction to the corresponding primary alcohol and partial oxidation to the target aldehyde . Another possibility is the direct reduction of the acyl precursor to the aldehyde . We did not detect linoleyl alcohol, neither labeled nor unlabeled, in the extracts, but this may be accounted for by immediate oxidation of the alcohol to the aldehyde, which would prevent accumulation to detectable amounts in the gland.
We have shown that linoleic acid is a direct precursor for the biosynthesis of Z7,Z10-16:Ald in C. valdiviana. We have not conclusively established the origin of linoleic acid used in pheromone biosynthesis, which might be either of dietary origin or be synthesized de novo, or a mixture of both. The chain-shortening of linoleic acid in the pheromone gland and the transformation of stearic acid to the pheromone compound suggests that the biosynthesis of Z7,Z10-16:Ald follows a pathway more similar to that for Type I lepidopteran pheromone compounds.