Most aphids possess intracellular bacteria of the genus Buchnera. The bacteria are transmitted vertically via the aphid ovary, and the association is obligate for both partners: Bacteria-free aphids grow poorly and produce few or no offspring, and Buchnera are both unknown apart from aphids and apparently unculturable. The symbiosis has a nutritional basis. Specifically, bacterial provisioning of essential amino acids has been demonstrated. Nitrogen recycling, however, is not quantitatively important to the nutrition of aphid species studied, and there is strong evidence against bacterial involvement in the lipid and sterol nutrition of aphids. Buchnera have been implicated in various non-nutritional functions. Of these, just one has strong experimental support: promotion of aphid transmission of circulative viruses. It is argued that strong parallels may exist between the nutritional interactions (including the underlying mechanisms) in the aphid-Buchnera association and other insect symbioses with intracellular microorganisms.

Nutritional Interactions in Insect-Microbial Symbioses: Aphids and Their Symbiotic Bacteria Buchnera

▪ Abstract This review covers selected literature from 1982 to the present on some of the ecological, behavioral, and biochemical aspects of hydrocarbon use by insects and other arthropods. Major ecological and behavioral topics are species- and gender-recognition, nestmate recognition, task-specific cues, dominance and fertility cues, chemical mimicry, and primer pheromones. Major biochemical topics include chain length regulation, mechanism of hydrocarbon formation, timing of hydrocarbon synthesis and transport, and biosynthesis of volatile hydrocarbon pheromones of Lepidoptera and Coleoptera. In addition, a section is devoted to future research needs in this rapidly growing area of science.

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Ecological, behavioral, and biochemical aspects of insect hydrocarbons*

Photosynthetic fixation of carbon dioxide in our biosphere yields approxi­ mately 136 X lOIS g of dry plant material annually, which represents Earth's most abundant form of biomass (88). Two major constituents of such biomass are cellulose and lignin, and hence this material is often referred to as . \ lignocellulosic biomass, or simply lignocellulose. Most of the synthesis (about 2/3) occurs in terrestrial ecosystems where it is balanced, or nearly so, by the decomposition/respiration side of the carbon cycle (63). Decom­ position of lignocellulose is carr ied out primarily by microorganisms, chiefly fungi and bacteria. However, augmenting the activities of microbes is an arr ay of soil macro-invertebrates, whose effects may range from simple comminution and dispersion of plant material to actual dissimilation of the structural polymers of lignocellulose (86, 90, 91). Among the most abundant and important of these invertebrates ' are termites, which, with their associated microbial symbionts, dissimilate a significant proportion of the cellulose

Role of Microorganisms in the Digestion of Lignocellulose by Termites

Lipids of the insect cuticle: origin, composition and function

The study of fat metabolism in insects has received considerable attention over the years. Although by no means complete, there is a growing body of information about dietary lipid requirements, and the absolute requirement for sterol is of particular note. In this review we (a) summarize the state of understanding of the dietary requirements for the major lipids and (b) describe in detail the insect lipid transport system. Insects digest and absorb lipids similarly to vertebrates, but with some important differences. The hallmark of fat metabolism in insects centers on the lipid transport system. The major lipid transported is diacylglycerol, and it is carried by a high-density lipoprotein called lipophorin. Lipophorin is a reusable shuttle that picks up lipid from the gut and delivers it to tissues for storage or utilization without using the endocytic processes common to vertebrate cells. The mechanisms by which this occurs are not completely understood and offer fruitful areas for future research.

Fat metabolism in insects

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.

Fatty acids in insects: Composition, metabolism, and biological significance

The chemistry, biochemistry, and physiology of insect cuticular lipids are reviewed. The types of components present in cuticular extracts are described with special emphasis on the occurrence and identification of the di- and trimethylalkanes and the newly discovered tetramethylalkanes. The methods used in the extraction of cuticular components are discussed, including recommendations to standardize procedures. The structural elucidation of methylalkanes, particularly the mass spectral interpretation of multi-methyl-branched alkanes, is reviewed. The biosynthesis of cuticular lipids is discussed with emphasis on the hydrocarbon components, describing elongation reactions and the origin of the methyl branches. The effects of environment and development on cuticular lipids are reviewed.

Mertxe de Renobales

Papers

Fatty acids in insects: Composition, metabolism, and biological significance

Chemistry, biochemistry, and physiology of insect cuticular lipids

Biosynthesis of linoleic acid in a termite, cockroach and cricket

De novo biosynthesis of linoleic acid in insects

Biosynthesis of linoleic acid in insects