Induction of the triploid silkworm, Bombyx mori, by ice-water treatment applied to eggs inseminated immediately after oviposition

Yokoyama, T.; Aizawa, M.; Oshiki, T.

The silkworm, Bombyx mori, used as experimental material was a hybrid of CT K cntdot Damb female (heterozygous normally pigmented egg, Sex-limited sable marking and heterozygous yellow blood larva: re/+re, T(W;2)p-Sa: +p +Y/+P Y) and re9 male (red pigmented egg, striped marking and white blood larva: re/re, p-S +GAMMA-y/p-S +Y). The eggs of the FCTK cntdot Camb times re9 hybrid were treated with ice-water at 0 degree C for 2 days immediately after oviposition. The treated eggs showes a normal or red pigmented in the ratio of 10.7:1, and the larvae hatched from normally pigmented eggs were females with striped marking and yellow blood of a percentage of 81.6. In spite of the fertilization of the individuals, these characters did not exhibit segregation for herozygous egg pigment (+re/re), blood color (Y/+y) and sex (ZW). Also, the number of sex-chromatin bodies per nucleus in the cells of the sucking stomach of these moths showed only the presence of one W chromosome. The eggs oviposited by many mot hs of the treated group showed considerable variation in shape and size, and died during subsequent embryonic development, without egg hatching. These results indicated that the triploid females (ZZW) were induced by ice-water treatment (0 degree C for 2 days) of the inseminated eggs immediately after oviposition. The induction of the triploid silkworm was ascribed to the inhibition of reduction division in the egg nucleus is inhibited by the ice-water treatment. As a result, the nucleus(ZW) of the diploid egg nucleus (ZW) fused with the pronucleus(Z) of the haploid sperm leading to the formation of a triploid female zygote (ZZW).