Neurohormonal Factors Involved in the Control of Pupariation

Abstract

Formation of the puparium (pupariation) is the first visible process in the initiation of metamorphosis of cyclorrhaphous flies. It is potentiated by the action of the molting hormone, supposedly produced and released by the ring gland, an endocrine organ comprising the homologues of the corpora allata, corpora cardiaca, and prothoracic glands. Fraenkel’s (1934, 1935) classic experiments with ligated Calliphora larvae revealed that hormonal conditions responsible for tanning of the cuticle are present many hours before the actual process begins. Larvae ligated before this “critical period” do not tan in the posterior region, which is devoid of the fused central nervous system (CNS) mass and of the ring gland. By using this ligation test, the hormone involved in the tanning reaction was isolated (Butenandt and Karlson 1954) and was recognized as a steroid compound, ecdysone (Huber and Hoppe 1965). The test has become known as the “Calliphora test.” Other fly species can be employed equally well, for instance, Sarcophaga spp. (Fraenkel and Žďárek 1970) or Musca domestica (Adelung and Karlson 1969), with even higher sensitivity in the latter case.