Unique chorion structure of the mottled gray (mgr) egg, an egg-character mutation of Bombyx mori (Lepidoptera: Bombycidae)

The surface and internal chorion structures of the mottled gray egg (mgr) of Bombyx mori, a mutation which exhibits patched areas of gray or opaque regions, were observed in comparison with normal eggs using a scanning electron microscope. No peculiarity was exhibited in the mutant with respect to whole egg size, surface structures at the micropyle region and basic patterns as well as the average area of the network imprints (polygons) on the lateral flat region. When cross-sections of the chorions were observed, the middle layer of the mgr chorion corresponding to the gray areas was found to be deformed without a lamellar structure. Thus it can be concluded that the mgr alleles take part in the formation of the middle layer architecture during choriogenesis.