Endocrine control of molting and metamorphosis in Bombyx mori

Insect molting and metamorphosis are controlled by ecdysteroids, produced by the prothoracic glands, and juvenile hormone (JH), produced by the corpora allata (CA). The production of ecdysteroid is stimulated by the prothoracicotropic hormone (PTTH). In recent several years, using silkworm, Bombyx mori as a model system, hormonal control of insect molting and metamorphosis has been studied. It is found that changes in hasal hemolymph ecdysteroid levels in this insect can modulate JH biosynthetic activity of (CA), with very low ecdysteroid levels during the early last larval instar leding to the inactivation of CA. It is also found that the PTTH signal transduction undergoes a development-specific change during the fourth and last larval instars. A review of the current knowledge on hormonal control of insect molting and metamorphosis has also been given.