Juvenile hormone modifies larvae and silk gland development in Bombyx mori.

Topical application of a Juvenile Hormone Analogue (ZR 515) during the first half of the first half of the last (fifth) larval instar of Bombyx mori induces a prolongation of this instar and increases larvae weight and silk secretion. Later treatment can lead to an extra larval molt. Moreover, the hormone analogue stops either the development or the secretory activity of the silk gland, depending on the period of treatments. When Juvenile Hormone is administered at the beginning of the fifth instar, silk gland growth as well as RNA and protein syntheses are first inhibited and later resumed and amplified. Finaly silk production increases up to 150 per cent of controls. One of the primarly effects of treatments seems to be RNA synthesis. Thus Juvenile Hormone analogue application could be a new tool for studying RNA transcription and/or processing.