Physiology of Insect Ecdysis

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Abstract
At the end of the last larval instar the mature silkworm larva stops feeding and spins a silken cocoon. In this chamber the animal subsequently pupates and in some cases overwinters in a dormant condition-termed diapause. Under the influence of the warmth and lengthening days of spring, the pupa terminates diapause and initiates adult development. Weeks later the mature moth sheds the pupal exuviae and escapes from the cocoon. In Cecropia (Hyalophora cecropia) and many other saturniids the larva has prepared for this eventuality by spinning into the cocoon an ‘escape-hatch’ or valve through which the moth emerges (Van der Kloot & Williams, 1953). Among the silkworms of the genus Antheraea the moth resorts to chemistry to escape from its stout-walled and valveless cocoon (Kafatos & Williams, 1964). A few days prior to emergence the moth secretes a crystalline enzyme, cocoonase, on to the surface of its maxillary galeae. Then, during the process of eclosion, buffer produced in the labial glands is also secreted on to the galeal surface. The resulting protease solution then digests the sericin ‘glue’ from around the silk fibres and thus provides an opening for the moth. After struggling free, the moth clings to the outside of the cocoon and spreads its wings.