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.