Insect Structure And Function

The physical form and body workings (Snodgrass 1935,1952; Wigglesworth 1984; Chapman 1982; Kerkut and Gilbert 1984; King and Akai 1982-1984; Manton 1977; Rockstein 1964-1974, 1978; Smith 1968; Treherne et al. 1963-1982) of insects and their terrestrial arthropod relatives are as remarkable and complex as those of any animal type. Numerous structural and functional systems will be used in the text following as organizational topics for a basic review.

References

Chapman, R. F. 1982. The insects: structure and function. 3d ed. American Elsevier, New York.

Kerkut, G. A., and L. I. Gilbert. 1984. Comprehensive insect physiology, biochemistry and pharmacology. Vols. 1 — 13. Pergamon, Elmsford, N.Y. King, R. C., and H. Akai, eds. 1982-1984. Insect ultrastructure. Vols. 1—2. Plenum, New York.

Manton, S. M. 1977. The Arthropoda, habits, functional morphology, and evolution. Clarendon, Oxford. Rockstein, M., ed. 1964-1974. The physiology of insects. Vols. 1—6. Academic, New York. Rockstein, M., ed. 1978. Biochemistry of insects. Academic, New York. Smith, D. S. 1968. Insect cells: Their structure and function. Oliver and Boyd, Edinburgh. Snodgrass, R. E. 1935. Principles of insect morphology. McGraw-Hill, New York. Snodgrass, R. E. 1952. A textbook of arthropod anatomy. Comstock, Ithaca. Treherne, J. E., M. J. Berridge, and V. B. Wigglesworth. 1963-1982. Advances in insect physiology. Vols. 1 — 16. Academic, New York.

Wigglesworth, V. B. 1984. Insect physiology. 8th ed. Chapman and Hall, London.

Integument

The outer, living epidermis in insects is a single layer of generally simple, cuboidal cells that secrete an external nonliving cuticle. The cuticle (Neville 1975) is very durable and resistant because of its composition of waterproof waxes and complex molecules of such substances as chitin (a nitrogenous polysaccharide) and sclerotin (protein). In combination with the epidermis, it forms the insect's integument (Hepburn 1976).

The integument may be generally thin and flexible, as in insect larvae, or thick and rigid, as in most adults and larval structures such as the head. Rigidity is the result of the abundance of sclerotin, and hard areas, or "sclerites," are said to be well sclerodzed. Flexibility is allowed by membranous joints or articulations between the rigid portions. Thus, the integument gives the insect its basic form and is its primary protective system, forming a barrier to water loss and entry of pathogenic microorganisms as well as providing resistance to physical trauma.

Sclerites may also be separated by infold-ings, known as apodemes (if linear, called sutures; if pitlike, apophyses). It is to the internal portions of apodemes that the main muscles of motion are attached, giving the integument a secondary function, that of a skeleton (exoskeleton).

The cuticle derives its color not only from its structural components but from infusions of pigments (Crowmartie 1959) and microstructural developments (lamellae, gratings, etc.) that cause scattering, refraction, and defraction of light waves striking them, resulting in spectral phenomena. Among the pigments are common colored compounds such as melanin (black), pterines (white, red, yellow), carotenoids (red, brown), carminic acid (carmine), and flavones (red, yellow). Physical colors are often metallic or iridescent blues, greens, and reddish hues. Many Neotropical butterflies are beautifully colored from combinations of both pigmentary and physical colors localized in the wing scales (Ghiradella 1984). Gold and silver are interference colors also, but unlike the other metallics, which are produced by pure, narrow wavelengths, these are broad-band reflective mixes of radiation (Neville 1975, 1977). By providing a surface for display of color patterns, the integument serves additional functions— protection by crypsis and mimicry, sexual recognition, and so forth.

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