HORMONAL-CONTROL OF MOLTING AND METAMORPHOSIS IN ARTHROPODS - ESTABLISHED FACTS AND OPEN QUESTION

The hormonal basis of molting and metamorphosis has been established a long time ago in insects, but our knowledge on other arthropod groups is not so well documented. Although ecdysteroids are for sure involved in these processes, molting glands are not yet identified in all groups, and the biosynthetic pathway from cholesterol to ecdysone is far from elucidated. Spectacular progress has been done on ecdysteroid receptors, and their formation of heterodimers with other DNA-binding proteins opens new concepts regarding the molecular mechanisms of gene activity regulation. Juvenile hormone synthesis (in corpora allata) was formerly restricted to insects, but more recently methyl farnesoate was found to be a secretory product of crustacean mandibular organs. It is also well known that juvenile hormone or synthetic analogs are active on ticks and more generally on lower arthropods. We are presently facing a rapidly developing knowledge of insect cellular and molecular endocrinology, particularly thanks to genetic and molecular biology approaches done on Drosophila. However, the most basic physiological questions regarding the mechanisms that trigger molting/metamorphosis, control larval stage number..., in other words everything what concerns the integrated functioning of endocrine systems remain still almost fully unknown.