Abstract
While many Plusiinae species commonly secrete (Z)-7-dodecenyl acetate (Z7-12:OAc) as a key pheromone component, female moths of the rice looper (Plusia festucae) exceptionally utilize (Z)-5-dodecenyl acetate (Z5-12:OAc) to communicate with their partners. GC–MS analysis of methyl esters derived from fatty acids included in the pheromone gland of P. festucae showed a series of esters monounsaturated at the ω7-position, i.e., (Z)-5-dodecenoate, (Z)-7-tetradecenoate, (Z)-9-hexadecenoate (Z9-16:Me), and (Z)-11-octadecenoate (Z11-18:Me). By topical application of D3-labled palmitic acid (16:Acid) and stearic acid (18:Acid) to the pheromone glands, similar amounts of D3-Z5-12:OAc were detected. The glands treated with D13-labeled monoenoic acids (Z9-16:Acid and Z11-18:Acid), which were custom-made by utilizing an acetylene coupling reaction with D13-1-bromohexane, also produced similar amounts of D13-Z5-12:OAc. These results suggested that Z5-12:OAc was biosynthesized by ω7-desaturase with low substrate specificity, which could introduce a double bond at the 9-position of a 16:Acid derivative and the 11-position of an 18:Acid derivative. Additional experiments with the glands pretreated with an inhibitor of chain elongation supported this speculation. Furthermore, a comparative study with another Plusiinae species (Chrysodeixis eriosoma) secreting Z7-12:OAc indicated that the β-oxidation systems of P. festucae and C. eriosoma were different.
Highlights
About 160,000 lepidopteran species are known world wide, and each species is believed to establish a species-specific mating communication system for species conservation
FATTY ACIDS IN THE PHEROMONE GLANDS Figure 2 shows the GC–MS analysis of fatty acid methyl esters (FAMEs) derived from lipids in the pheromone gland of P. festucae females
In Lepidoptera, biosynthesis of Type I pheromones has been studied with several species and the results have proposed the following pathway operating in pheromone glands; formation of saturated fatty acyl compounds from acetyl CoA → desaturation → chain shortening or elongation → reduction of the acyl moiety to a hydroxyl group → acetylation of alcohols or oxidation to aldehydes (Jurenka, 2004)
Summary
About 160,000 lepidopteran species are known world wide, and each species is believed to establish a species-specific mating communication system for species conservation. Lepidopteran sex pheromones have been identified from more than 600 moth species and about three-quarters of them are composed of C10–C18 unsaturated fatty alcohols, their acetates, and aldehyde derivatives, including one, two, or three C=C bonds (Type I pheromones; Ando et al, 2004; Ando, 2011; El-Sayed, 2011) These components are biosynthesized from saturated fatty acyl intermediates, into which double bonds are introduced at definite positions by desaturases working in a pheromone gland (Jurenka, 2004). In addition to the different chain lengths and kinds of terminal functional groups, the chemical structural varieties are attributed to the different positions of the double bonds (Ando et al, 2004)
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