Biosynthesis of Unusual Moth Pheromone Components Involves Two Different Pathways in the Navel Orangeworm, Amyelois transitella

Abstract

The sex pheromone of the navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), consists of two different types of components, one type including (11 Z,13 Z)-11,13-hexadecadienal (11 Z,13 Z-16:Ald) with a terminal functional group containing oxygen, similar to the majority of moth pheromones reported, and another type including the unusual long-chain pentaenes, (3 Z,6 Z,9 Z,12 Z,15 Z)-3,6,9,12,15-tricosapentaene (3 Z,6 Z,9 Z,12 Z,15 Z-23:H) and (3 Z,6 Z,9 Z,12 Z,15 Z)- 3,6,9,12,15-pentacosapentaene (3 Z,6 Z,9 Z,12 Z,15 Z-25:H). After decapitation of females, the titer of 11 Z,13 Z-16:Ald in the pheromone gland decreased significantly, whereas the titer of the pentaenes remained unchanged. Injection of a pheromone biosynthesis activating peptide (PBAN) into the abdomens of decapitated females restored the titer of 11 Z,13 Z-16:Ald and even increased it above that in intact females, whereas the titer of the pentaenes in the pheromone gland was not affected by PBAN injection. In addition to common fatty acids, two likely precursors of 11 Z,13 Z-16:Ald, i.e., ( Z)-11-hexadecenoic and (11Z,13Z)-11,13-hexadecadienoic acid, as well as traces of ( Z)-6-hexadecenoic acid, were found in gland extracts. In addition, pheromone gland lipids contained (5 Z,8 Z,11 Z,14 Z,17 Z)-5,8,11,14,17-icosapentaenoic acid, which also was found in extracts of the rest of the abdomen. Deuterium-labeled fatty acids, (16,16,16-D ₃)-hexadecanoic acid and ( Z)-[13,13,14,14,15,15,16,16,16-D ₉]-11-hexadecenoic acid, were incorporated into 11 Z,13 Z-16:Ald after topical application to the sex pheromone gland coupled with abdominal injection of PBAN. Deuterium label was incorporated into the C ₂₃ and C ₂₅ pentaenes after injection of (9 Z,12 Z,15 Z)- [17,17,18,18,18-D ₅]-9,12,15-octadecatrienoic acid into 1–2 d old female pupae. These labeling results, in conjunction with the composition of fatty acid intermediates found in pheromone gland extracts, support different pathways leading to the two pheromone components. 11 Z,13 Z-16:Ald is probably produced in the pheromone gland by Δ11 desaturation of palmitic acid to 11 Z-16:Acid followed by a second desaturation to form 11 Z,13 Z-16:Acid and subsequent reduction and oxidation. The production of 3 Z,6 Z,9 Z,12 Z,15 Z-23:H and 3 Z,6 Z,9 Z,12 Z,15 Z-25:H may take place outside the pheromone gland, and appears to start from linolenic acid, which is elongated and desaturated to form (5 Z,8 Z,11 Z,14 Z,17 Z)-5,8,11,14,17-icosapentaenoic acid, followed by two or three further elongation steps and finally reductive decarboxylation.