Plate 1 A unit of the castor oil stearoyl-ACP desaturase, with a molecule of stearic acid (white stick model, grey space-filling outline) modelled into the active site, in a gauche conformation. The protein chain with its a-helix coils is shown green. This conformation orients both C-9 and C-10 pro-R hydrogens towards the activated oxygen (not shown), bound to the di-iron active site (red spheres) allowing removal of hydrogen and introduction of a cis double bond (Illustration: J. Shanklin and W. McGrath, Brookhaven Natl. Lab.)

Plate 2 Female silkworm moth Bombyx mori with her pheromone glands extended (arrowed), emitting bombykol

(Photo: Jacques Six, with permission of Société Nouvelle des Éditions Boubée)

Plate 3 The seven-spotted ladybird Coccinella septempunctata, which produces precoccinelline and coccinelline by reflex bleeding. The larva, left (Photo: Jim Kalish) Adults mating, right (Photo: Steve McWilliam)

Plate 4 Pupa of the Mexican bean beetle Epilachna varivcstis, showing its many hairs with droplets of fluid containing epilachnine and related macrocyclic compounds; and a close-up view of some of the hairs and droplets (Photo: Maria Eisner)

Plate 5 The centipede Scolopendra subspinipes multilans which produces the antibiotic centipedin. It also has an extremely painful bite of unknown composition (Photo: Tom Larsen)

Plate 6 The boll weevil Anthonomis grandis, an important pest of cotton and producer of a terpene aggregation pheromone. Insects are a favoured subject for philately

Plate 7 Larva of the ladybird Hippodamia convergens, which produces hippodamine and convergine, eating aphids of Aphis nerii, which in turn live on oleander bushes, and are pigmented with the naphthol glucoside B (Figure 8.17). This aphid collects and stores three cardiac glycosides from oleander (Photo: Mike Quinn)

Plate 8 Wax mounds on an Acacia branch produced by Ceroplastes scale insects. Anoplolepis ants are searching the branch (Photo: Hamish Robertson)

Plate 9 The fire bug Pyrrhocorus apterus coloured by red erythropterin pigment and other pterins

(Photo: Anthony Papadopoulos)

Plate 10 The blister beetle Lytta magister which produces cantharidin (Photo: Warren E. Savary)

Plate 11 Larva of the moth Arctia caja, with its long urticating hairs, which contain the alkaloid serotonin (Photo: Jens Christian Schou)

Plate 12 Larva of the Monarch butterfly Danaus plexippus, with aposematic (warning) colours. The larva acquires the cardiac glycoside calotropin from its food plant (Photo: Mike Quinn)

Plate 13 The millipede Harpaphe haydeniana, a producer of hydrogen cyanide. It has been used to study the biosynthesis of mandelonitrile (Photo: Markku Savela)

Plate 14 Adult female lone star tick Amblyomma americanum, which produces 2,6-dichlorophenol as a sexual attractant (Photo: School of Veterinary Medicine, State U. Oklahoma)

Plate 15 Larva of the tobacco hornworn Manduca sexta (Photo: Paul Choate)

Plate 16 Two adult wasps o/ Polistes dominulus on a newly constructed nest. Their yellow colour is due to xanthopterin. The upper wasp is marking the pedicel of the nest with abdominal secretion (Photo: Stefano Turillazzi)

Plate 17 Adults and nymphs of the milkweed bug Oncopeltus fasciatus on a milkweed pod.

Their cuticle is partly black (melanin) and partly transparent, showing the pterin pigments underneath (Photo: Mike Quinn)

Plate 18 A worker of the garden ant Myrmica rubra following an artificial trail of synthetic 3-ethyl-2,5-dimethylpyrazine on paper. Note the position of the antennae. The sting lance is protruded, probably re-enforcing the trail with more pheromone. The paper is ruled in 0.1 inch (2.54 mm) squares (Photo: Terry Bolam)

Figure 7.14 A summary of the formation of the moulting hormone 20-hydroxyecdysone from cholesterol The early stages are not yet firmly known. All the stages except the last occur in the prothoracic gland. Ponasterone A is a crustacean moulting hormone

hydroxyl. Ecdysteroids are inactivated by conversion to C-22 sulphates or oxidized to ecdysonoic acid (Figure 7.15) or to a lesser extent converted to glycosides.

In some arthropods (for this hormone is shared with other classes besides insects), the series are not hydroxylated at C-25. Many crustaceans use 20-hydroxyecdysone as moulting hormone, others use ponasterone A (Figure 7.14). Ecdysteroids have also been found in plants. These phytoecdysteroids are widely distributed in the plant

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