Effect of X-ray irradiation on the male moths of two voltine groups of the silkworm, Bombyx mori, and inheritance of induced sterility

Full text: The silkworm, Bombyx mori, one of the important sericigenous insect members, during its life cycle from egg to adult exhibits sequential events of spermatogenesis in homogametic males and mature sperms are invariably seen in adult moths. In the present experiment, the male moths of two races of Bombyx mori viz., Pure Mysore and Kalimpong-A belonging to two voltine groups namely multivoltine and bivoltines, respectively were irradiated with X-rays at two independent doses of 50 Gy and 100 Gy and were crossed with unmated female moths. Untreated batches were maintained as control. The eggs deposited by bivoltine race were treated with hydrochloric acid to break the diapause and were allowed to develop at 25±1 deg. C and 80% RH. Unfertilised and unhatched eggs of both the parental races were examined by adopting standard procedures and the hatched larvae were reared under standard rearing conditions. In order to understand the inherited sterility, the untreated females were crossed with F1, F2 and F3 males survived from X-ray treatment. The results have clearly indicated that, in the parental generation, unfertilised and unhatched eggs ranged from 65-75% with the multivoltine race revealing fewer of embryonic deaths and unfertilised eggs and in both races a dose dependency was found. The eggs laid by F1 moths recorded the highest number of unfertilized and unhatched eggs while in F2 and F3 populations there was a gradual decline in the sterility resulting in a significant increase in egg hatch. The data obtained were statistically analysed at every generation and compared with those of untreated control batches. The high percentage of sterility in the treated F1 and inherited sterility in F2 and F3 populations are discussed in the light of chromosome imbalance (translocation) that may be able to pass through meiotic division in adult moths, which may cause production of functionless sperms resulting in delayed lethal effect from irradiation. The differences in the response to radiation by the moths of two voltinistic groups are also discussed. (author)