Differences in oxidase and esterase activities involved in pheromone biosynthesis in two species ofChoristoneura

Biosynthetic pathways of the sex pheromone components and substrate selectivity of the oxidation enzymes working in pheromone glands of the fall webworm, Hyphantria cunea

The fall webworm, Hyphantria cunea Drury (Lepidoptera: Arctiidae), is a harmful polyphagous defoliator. Female moths produce the following four pheromone components in a ratio of about 5:4:10:2; (9Z,12Z)-9,12-octadecadienal (I), (9Z,12Z,15Z)-9,12,15-octadecatrienal (II), cis-9,10-epoxy-(3Z,6Z)-3,6-henicosadiene (III), and cis-9,10-epoxy-(3Z,6Z)-1,3,6-henicosatriene (IV). Although ¹³C-labeled linolenic acid was not converted into trienal II at the pheromone glands of H. cunea females, GC-MS analysis of an extract of the pheromone gland treated topically with ¹³C-labeled linolenyl alcohol showed the aldehyde incorporating the isotope. Other C₁₈ and C₁₉ fatty alcohols were also oxidized to the corresponding aldehydes in the pheromone gland, indicating a biosynthetic pathway of IIvia linolenyl alcohol and low substrate selectivity of the alcohol oxidase in the pheromone gland. On the other hand, epoxydiene III was expected to be produced by specific 9,10-epoxidation of the corresponding C₂₁ trienyl hydrocarbon, which might be biosynthesized from dietary linolenic acid in oenocytes and transported to the pheromone gland. The final biosynthetic step in the pheromone gland was confirmed by an experiment using deuterated C₂₁ triene, which was synthesized by the chain elongation of linolenic acid and LiAlD₄ reduction as key reactions. When the labeled triene was administered to the female by topical application at the pheromone gland or injection into the abdomen, deuterated III was detected in a pheromone extract by GC-MS analysis. Furthermore, the substrate selectivity of epoxidase and selective incorporation by the pheromone glands were examined by treatments with mixtures of the deuterated precursor and other hydrocarbons such as C₁₉-C₂₃ trienyl, C₂₁ dienyl, and C₂₁ monoenyl hydrocarbons. The 9,10-epoxy derivative of each alkene was produced, while the epoxidation of the C₂₁ monoene was poorer than those of the trienes and diene. The low selectivity indicated that the species-specific pheromone of the H. cunea female was mainly due to the critical formation of the precursor of each component.

Insect pheromones--an overview of biosynthesis and endocrine regulation

This overview describes, compares, and attempts to unify major themes related to the biosynthetic pathways and endocrine regulation of insect pheromone production. Rather than developing and dedicating an entirely unique set of enzymes for pheromone biosynthesis, insects appear to have evolved to add one or a few tissue-specific auxiliary or modified enzymes that transform the products of "normal" metabolism to pheromone compounds of high stereochemical and quantitative specificity. This general understanding is derived from research on model species from one exopterygote insect order (Blattodea) and three endopterygote insect orders (Coleoptera, Diptera, and Lepidoptera). For instance, the ketone hydrocarbon contact sex pheromone of the female German cockroach, Blattella germanica, derives its origins from fatty acid biosynthesis, arising from elongation of a methyl-branched fatty acyl-CoA moiety followed by decarboxylation, hydroxylation, and oxidation. Coleopteran sex and aggregation pheromones also arise from modifications of fatty acid biosynthesis or other biosynthetic pathways, such as the isoprenoid pathway (e.g. Cucujidae, Curculionidae, and Scolytidae), or from simple transformations of amino acids or other highly elaborated host precursors (e.g. Scarabaeidae and Scolytidae). Like the sex pheromone of B. germanica, female-produced dipteran (e.g. Drosophilidae and Muscidae) sex pheromone components originate from elongation of fatty acyl-CoA moieties followed by loss of the carbonyl carbon and the formation of the corresponding hydrocarbon. Female-produced lepidopteran sex pheromones are also derived from fatty acids, but many moths utilize a species-specific combination of desaturation and chain-shortening reactions followed by reductive modification of the carbonyl carbon. Carbon skeletons derived from amino acids can also be used as chain initiating units and elongated to lepidopteran pheromones by this pathway (e.g. Arctiidae and Noctuidae). Insects utilize at least three hormonal messengers to regulate pheromone biosynthesis. Blattodean and coleopteran pheromone production is induced by juvenile hormone III (JH III). In the female common house fly, Musca domestica, and possibly other species of Diptera, it appears that during hydrocarbon sex pheromone biosynthesis, ovarian-produced ecdysteroids regulate synthesis by affecting the activities of one or more fatty acyl-CoA elongation enzyme(s) (elongases). Lepidopteran sex pheromone biosynthesis is often mediated by a 33 or 34 amino acid pheromone biosynthesis activating neuropeptide (PBAN) through alteration of enzyme activities at one or more steps prior to or during fatty acid synthesis or during modification of the carbonyl group. Although a molecular level understanding of the regulation of insect pheromone biosynthesis is in its infancy, in the male California fivespined ips, Ips paraconfusus (Coleoptera: Scolytidae), JH III acts at the transcriptional level by increasing the abundance of mRNA for 3-hydroxy-3-methylglutaryl-CoA reductase, a key enzyme in de novo isoprenoid aggregation pheromone biosynthesis.