Abstract: The female moths of 157 bred and hybrid lines of the silkworm, Bombyx mori, which are maintained in the gene pool of Southwest University, China, were dissected, and the diversity in their ovariole number was investigated. Variation in ovariole number of the ovaries of female moths was detected in 87 of the 157 (55.4%) bred/hybrid lines, and 11 mutant types of ovariole number were found. The proportion of individuals with atypical ovariole number showed significant differences among the bred/hybrid lines surveyed. The highest proportion (60.19%) was found in the mutant lines and the lowest (37.50%) in the hybrid lines. In the mutant lines with different ovariole numbers of the ovaries of female moths, the proportions ranged from 2% to 50%. Observations on some bred/hybrid lines revealed that the increase in ovariole number in the line was not necessarily accompanied by an increase in total eggs produced and that the average egg number per ovariole was always lower than that of the normal type (4, 4). The results of analysis on the variation in ovariole number of three successive generations of the commercially reared bred line 21-871 and the mutant line 06-051 suggested that variation in ovariole number is inheritable.

Key words: Bombyx mori, bred/hybrid lines, ovariole number, variation, reproductive significance