1991 Volume 26 Issue 3 Pages 299-306
Abnormal sex-ratio (SR) condition was found in Gastrolina depressa in natural populations. Average hatchability of egg masses laid by SR and normal (NR) females was 47% and 92%, respectively. The male ratio in progenies was 0.3% in SR type and 48% in NR type. Egg masses laid after 16 days by normal females injected with resuspended pellet of SR ovaries tended to become SR. The SR agent(s) in G. depressa was sensitive only to tetracycline among four antibiotics tested. No SR colonies were found in Hokkaido, Shikoku or Kyusyu. SR colonies have been found in limited areas at a northernmost limit of Fukushima and at a southernmost limit of Gifu, Central Honshu. No SR colonies were found in the Tohoku, Kinki and Chugoku districts in Honshu.
