Section 16
Chapter 15,564

Ecdysteroid levels and developmental events during larval moulting in the silkworm, Bombyx mori

Kiguchi, K.; Agui, N.

Journal of Insect Physiology 27.11: 805-812


ISSN/ISBN: 0022-1910
DOI: 10.1016/0022-1910(81)90072-x
Accession: 015563139

In the silkworm, B. mori , apolysis of the spiracle is the first visible sign of the initiation of a larval moult. After spiracular apolysis, the characteristic sequence of new spiracle formation can be recognized easily through the cuticle around the old spiracle. This sequence, called the spiracle index, was used as the basis for a precise developmental chronology of the larval moulting period. At certain spiracle-index stages, histological changes in the larval ventral abdominal integument were also examined. By allatectomy and abdominal ligations, the critical periods for the secretion of juvenile hormone and ecdysone respectively were found to be at the initiation of spiracular apolysis and at the time when general apolysis was complete. The haemolymph-ecdysteroid level as measured by radioimmunoassay was about 30-50 ng/ml during the first 2 days of the 4th instar, 60-70 ng/ml at the time of initiation of spiracular apolysis, and 200 ng/ml at the time of completion of apolysis of the general body surface. The maximal level of the hormone was about 290 ng/ml at the mid-moulting period. The relationship between the ecdysteroid titre and morphological events occurring during the larval moult was discussed.

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