Fluctuations in the biosynthetic activity of the prothoracic gland in recessive trimolters of the silkworm,Bombyx mori: Their modulation by juvenile hormone and physiological significance

✍ Scribed by Gu, Shi-Hong ;Chow, Yien-Shing ;Lin, Fei-Jann

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 940 KB
• Volume: 271
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402710308

✦ Synopsis

Abstract

Changes in the steroidogenic competence of prothoracic glands and their modulation by juvenile hormone (JH) were examined in recessive trimolters(rt)of the silkworm, Bombyx mori. These rt mutants have four larval instars rather than the five larval instars of normal silkworms. A small peak of prothoracic gland activity was found to occur during the early stage of the last (fourth) larval instar. The activities of both the prothoracic gland and the corpora allata (CA) were, however, greatly inhibited during the third instar after the third instar larvae have been treated with an imidazole compound (KK‐42). No small peak of prothoracic gland activity was detected during the early stage of the last instar in these treated larvae. The pattern of secretion from the prothoracic gland during the third instar was not significantly affected when hydroprene was applied to the KK‐42‐treated larvae during the prolonged third instar. However, the same small peak of activity, as found in untreated rt larvae, was detected during the early last instar. A model was developed from the results of the present study which clearly shows how the slight fluctuations in the activity of the prothoracic gland are regulated. By treating newly ecdysed last instar larvae with KK‐42 and by the addition of 20‐hydroxyecdysone to the food supplied to these larvae, we conclude that the decrease after small increase in the ecdysteroid titers and subsequent low ecdysteroid levels during the early last larval instar play an important role in initiating the decline of the JH biosynthetic rate and in directing precocious metamorphosis. © 1995 Wiley‐Liss, Inc.