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FIGURE 18.2 Modifications of the distal tip of the proboscis in fruit-piercing and skin-piercing moths. (A) Unmodified proboscis of nectar-sucking moth, Autographa gamma. (Noctuidae); (B), Fruit-piercing moth, Scolyopteryx libatrix (Noctuidae); (C) skin-piercing, blood-sucking moth, Calyptra eustrigata (Noctuidae). (Redrawn from Bànziger, 1971.)

for chewing plant material on which the larvae feed. The general body form of larvae is highly modified in some families to the extent that they may not be recognized as lepidopteran larvae by the nonspecialist. Examples include some of the more medically important taxa such as puss caterpillars and hag moths.

Caterpillars which cause dermatitis on contact with vertebrate skin are protected by specialized hairs and spines. In some cases these structures cause simple mechanical injury or irritation when they penetrate the skin. In other cases, they have associated poison glands which

Crochets

FIGURE 18.3 External morphology of typical lepidopteran larva, with enlargement of abdominal proleg showing tiny hooks, or crochets. (Redrawn from Romoser, 1981.)

Crochets

FIGURE 18.3 External morphology of typical lepidopteran larva, with enlargement of abdominal proleg showing tiny hooks, or crochets. (Redrawn from Romoser, 1981.)

secrete toxic substances that elicit varying degrees of inflammation and swelling at the contact site. The location, numbers, and types of urticating hairs and spines vary significantly among different families and genera (Fig. 18.4).

Setae and spines are produced by specialized trichogen cells, literally "hair-forming" cells. These cells secrete multiple layers of cuticle to form the wall structure, differentiated from the surrounding epidermis. Each spine typically articulates with a socket formed by a tormogen cell, or "socket-forming" cell. Setae, or hairs, are generally formed by one or a few trichogen cells, whereas the larger, more robust spines are multicellular in origin and are produced by many trichogen cells. These setae and spines usually are innervated and associated with supporting cells and, depending on the taxon, may or may not have poison-secreting cells and tracheoles.

The specialized setae and spines of urticating lepi-dopterans are highly variable in structure. The following categories are based on Kawamoto and Kamada's (1984) modification of a classification proposed by Kano (1967, 1979), which includes types found in adults as well as larvae. According to their classification, there are two major groups of urticating structures: spicule hairs and spine hairs. Spicule hairs are detachable setae which are readily rubbed off or can become airborne to cause dermatitis on contact with animal skin. These hairs are easily shed and often are incorporated into the silk of the pupal cocoon. Although some of them cause only mechanical injury, others contain toxins which can affect vertebrates on contact. Spine hairs, on the other hand, cause urticaria only when the caterpillar makes direct contact with the skin. They often have associated poison glands and must be innervated in order for the toxins to be released. The following seven types of spicule hairs and four types of spine hairs are recognized.

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