Arthropods And Insects

The arthropods were the first organisms to emerge from the sea, and insects were the first invertebrates to fly. The arthropods consist of Crustacea (crabs, lobsters, shrimp, barnacles and woodlice), Chelicerata (spiders, ticks, mites, scorpions and others), Hexapoda or Insecta, and Myriapoda (millipedes, centipedes and other minor groups). These classes separated a long time ago, so they have developed quite differently, but it is interesting to discover parallel developments.

Spiders and millipedes have sometimes developed chemical defences or communication chemicals similar to those of insects. It is therefore useful occasionally to make comparisons.

The insects are the largest single group of animals, with over 800,000 identified species, far more than all the other animals put together. New species are reported at the rate of about 5,000 per year, and total number estimates range from 1 to 10 million. It is estimated there are 1018 individuals alive at any time. They are divided into the Apterygota, primitive wingless insects (springtails and silverfish) which have as yet received little chemical study; and the Pterygota, or winged insects, which form the great majority. The latter in turn are divided into the Exopterygota or Hemimetabola, which hatch from eggs to nymphs which closely resemble their final adult form or imago (grasshoppers, cockroaches, termites, bugs, stick insects, etc.) (Figure 1.5); and Endopterygota or Holometabola, which hatch from egg to larvae which may have a very different form and habitat from the adult. They then go into a resting form called the pupa, while the tissues are completely remodelled and from that emerges the adult form (Figure 1.5). The Holometabola include beetles, butterflies and moths, flies, fleas, bees, wasps and ants. Almost half of all the insect species are beetles. Potentially, the subject of this book is gigantic.

The isolation of insect chemicals began slowly. Kermesic acid or Venetian red, a pigment from beetles (Chapter 8) has been known and used from ancient times. Wray, in 1670, reported formic acid by distillation of formicine ants. It was not until the 1930s that it began to be recognized that some Lepidoptera males were chemically attracted to females, and

Figure 1.5 Representation of the life cycles of a hemimetabolous and a holometabolous insect. The symbols JH and MH between stages indicate where the juvenile hormone (Chapter 6) and moulting hormone (Chapter 7), which regulate development, are produced

Reprinted from Comprehensive Natural Products Chemistry, Vol. 8, E. D. Morgan and I. D. Wilson. Insect hormones and insect chemical ecology, pp. 263-375. Copyright 1999, with permission from Elsevier.

only in 1956 was the first sexual attractant (bombykol, from the silk moth Bombyx morĂ­) isolated and identified. From that time onward, with the development of chromatographic and sensitive mass spectrometric techniques, the study of insect natural products has grown to be a major discipline of science.

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  • Osman
    What other defense secretion produce by arthropods?
    5 months ago

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