Comparison of Chorion Structure of Eggs from Bombyx mori, Bombyx mandarina (Lepidoptera: Bombycidae) and Their First Filial Generation

Abstract

The surface and internal structures of eggshells were compared among Bombyx mori, Bombyx mandarina and their first filial generation (F₁) using a scanning electron microscope. The average area of petal-shaped patterns directly surrounding the micropyle opening at the anterior pole region of the egg surface, and that of polygons imprinted on the lateral flat sides, were significantly smaller in B mandarina and F 1 than in B. mori. The knobs clearly observable in each polygon of B. mori were very few in number in B. mandarina and F₁. The knobs appearing on the surface at the posterior pole, dorsal side and ventral side regions of B. mandarina and F₁ were large and irregular in shape. Moreover, cross sections of B. mandarina chorion revealed mountain-like peaks with an air cavity, a feature never seen in B. mori eggs. This peculiar structure was also found in the F₁ eggs, indicating that the character is inherited dominantly from B. mandarina. The differences in eggshell morphology between the two species may reflect their distinct habitats.