Ameiotic and meiotic parthenogenesis induced by carbonated water was investigated using ovarian eggs of the silkworm, Bombyx mori. We used B. mori females in which the red egg gene locus is heterozygous (+/re) in order to facilitate detection of parthenogenesis via egg pigmentation. More than 80% of the ovarian eggs from virgin females exhibited parthenogenesis when maintained at 17ﾟC for 1 day, soaked in carbonated water for 1 h at 17ﾟC, and subsequently maintained at 17ﾟC or 3 days. When ovarian eggs were soaked in carbonated water adjusted to different pH values, parthenogenesis was significantly increased in the acidic pH range where CO2 bubbles were generated in the water. Because eggs soaked in acidified non-carbonated mineral water exhibited a significantly lower induction rate, CO2 gas in carbonated water, rather than hydrogen ions, was suggested to play more important role in parthenogenesis induction. Sealing the front pole, back pole, lateral side, whole part, and no part of ovarian eggs with nail varnish (topcoat) to inhibit CO2 diffusion into the eggs resulted in 79.1%, 93.1%, 82.4%, 0%, and 84.4% egg parthenogenesis, respectively. These findings suggest that gaseous CO2 from carbonated water, penetrating eggs via unspecified surface areas, induces ameiotic parthenogenesis. In general, the hatchability of parthenogenetic eggs was very low. We hypothesize that embryonic lethality arises from haploid cells in parthenogenetic embryos.
