Embryonic Diapause Of B Mori

Silkworms undergo diapause, during which the embryo within the egg stops growing. In the B. mori embryo, diapause is primarily determined by the temperature, light, nutrition, and other conditions of the lifetime of silkworms. Of the various factors, temperature and light during the egg (embryo) stage have the greatest influence. When the eggs of bivoltine silkworms were incubated at relatively high temperatures (25°C) with long days (> 13 h of light), all silkworms that grew from these eggs laid diapausing eggs. When the eggs were incubated at 15°C with short days (< 13 h of light), adults of all these silkworms subsequently laid nondiapausing eggs.

The subesophageal ganglion, located just below the brain, secretes a peptide hormone that induces the embryonic diapause of B. mori. In 1951, K. Hasegawa and S. Fukuda, in separate studies, demonstrated that the subesophageal ganglion plays role in induction of diapause. The diapause hormone is composed of 24 amino acids and is produced and secreted by six pairs of neurosecretory cells of the subesophageal ganglion.

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