No abstract

The composition, metabolism, and significance of fatty acids in insect biology are addressed. Fatty acids enter a number of metabolic pathways not directly related to energy storage and production; the unifying theme is that the fatty acids are not only structurally altered in these pathways, but that the alterations carry them from one area of biological significance into another. This theme is developed by offering a perspective on fatty acids in insects and then reviewing three major areas: 1) fatty acid composition, 2) biosynthesis of fatty acids (including polyunsaturated fatty acids and characteristics of certain biosynthetic enzymes), and 3) the biological significance of fatty acids. This last section includes discussions of the biochemistry of waxes, pheromones, and prostaglandins and the roles of fatty acids as components of defensive secretions. Little is known at the biochemical level about the regulation of fatty acid metabolism, and it is suggested that work in this area represents another frontier in insect biochemistry.

Pheromones are utilized by many insects in a complex chemical communication system. This review will look at the biosynthesis of sex and aggregation pheromones in the model insects, moths, flies, cockroaches, and beetles. The biosynthetic pathways involve altered pathways of normal metabolism of fatty acids and isoprenoids. Endocrine regulation of the biosynthetic pathways will also be reviewed for the model insects. A neuropeptide named pheromone biosynthesis activating neuropeptide regulates sex pheromone biosynthesis in moths. Juvenile hormone regulates pheromone production in the beetles and cockroaches, while 20-hydroxyecdysone regulates pheromone production in the flies.

Pheromone biosynthesis-activating neuropeptide (PBAN), a peptide produced by the subesophageal ganglion, is used by a variety of moths to regulate pheromone production. PBAN acts directly on pheromone gland cells by using calcium and cAMP as second messengers. We have identified a gene encoding a G proteincoupled receptor (GPCR) from pheromone glands of the female moth Helicoverpa zea. The gene was identified based on sequence identity to a group of GPCRs from Drosophila that are homologous to neuromedin U receptors in vertebrates. The full-length PBAN receptor was subsequently cloned, expressed in Sf9 insect cells, and shown to mobilize calcium in response to PBAN. This response was dose-dependent (EC 50 ‫؍‬ 25 nM) with a maximum response at 300 nM and a minimal observable response at 10 nM. Four additional peptides produced by the PBAN-encoding gene were also tested for activity, and it was determined that three had similar activity to PBAN and the other was slightly less active. Peptides belonging to the same family as PBAN, namely pyrokinins, as well as the vertebrate neuromedin U peptide also induced a calcium response. We have identified a GPCR for the PBAN͞pyrokinin family of peptides with a known function of stimulating pheromone biosynthesis in female moths. It is related to several receptors from insects (Drosophila and Anopheles) and to neuromedin U and ghrelin receptors from vertebrates.