Cuticle of insect

The external cuticle of insects is covered by a waxy layer composed of mixtures of hydro-phobic lipids that include long-chain alkanes, alkenes, wax esters, fatty acids, alcohols, aldehydes, and sterols. The primary purpose of this layer is to maintain water balance and prevent desiccation, as described in Chapter 6, but many of the cuticular lipid components have important secondary roles as intraspecific contact chemical signals (pheromones). These roles include species and sex recognition during reproductive interactions, and nestmate recognition and other colony organization functions in social insects. Thus, these compounds are essential mediators of insect behaviors. Cuticular compounds are also exploited by parasitoids and predators as interspecific contact cues (kairomones) to aid in host location. 

Hydrocarbons found in the environment are of diverse structure and are widely distributed in the biosphere, predominantly as surface waxes of leaves, plant oils, cuticles of insects, and the lipids of microorganisms. Straight-chain HC, or alkanes, with carbon number maxima in the range of C17 to C21 are typically produced by aquatic algae. Conversely terrestrial plants typically produce alkanes with C25 to C33 maxima. Plants also synthesize aromatic HC such as carotenoids, lignin, aUcenoids, terpenes, and flavenoids. Polycyclic... 

Lipids also function as antimicrobial agents in the skin of mammals (Nico-laides, 1974), antidesiccants in the cuticle of insects (Holloway, 1984), and bioacoustic lenses in dolphins (Ackman et al., 1975). A special structure known as the elaisome located in the seeds of numerous species of plants release lipids, particularly diacylglycerols, that attract ants (Marshall et al., 1979). A study by Skidmore and Heithaus (1988) used TLC to show that ants responded rapidly to the elaisomes or the diacylglycerol fraction of the elaisomes of seeds of the perennial herb Hepatica americana. 

Oxidation catalysed by peroxidases (Figure 2.35) converts the tyrosine residues in proteins into bityrosine and isobityrosine derivatives. Bityrosine has been found in animal proteins from resilin, a protein found in the cuticle of insects and arthropods, to... 

Chitin is a (l->4)-linked 2-acetoamido-2-deoxy-g-D-glucan, and chitosan is its N-deacetylated product. These polysaccharides are naturally abundant and are present in the cuticles of insects and in the cell walls of plant pathogens, absent in the higher plant kingdom. Chitin and chitosan are (a) natural, (b) biocompatible, (c) almost nontoxic, (d) biodegradable, and (e) bioactive polymers. Our interest in these polymers is two-fold. (1) the molecular design of chitin and chitosan by chemical modification (Figure 1) in view of (a) the inversion of their molecular conformation, 3 (b) the development of their potential molecular... 

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