| Due to the robustness of the male silkworm larvae, strong vitality of its pupae, high rate of cocoon layer they produced, long ,fine and evenly distributed silk fibers, the rate of silk produced by the male silkworm is about 20% more than that of the female; the grade of silk produced from silk fiber spu/7 by the male silkworm is raised to more than 2 grades than that of the silk fiber spun by mixed sexes, reaching to the level of 5A; what's more, the male silkworm produce quality cocoon and need 15% less of the amount of mulberry than the mixed sexes (Huang Junting,1980). For all the above-mentioned advantages in rearing of the male silkworm, one of the key measures in sericultural practice is the attempt to realize the monoculture of male silkworm, which will both raise the quality of the cocoons and reduce the cost for silk production. For these purposes, the selective breeding of male silkworm races has always been one of the focuses in sericulture of many sericologists home and abroad.In order to realize the monoculture of male silkworm, many researchers across the world have attempted and are still attempting to look for effective means, e.g. parthenogenesis (Pan Shaoxi,1996), male nucleus development (Li Muwan et al., 1996), using balanced lethal systems(Xia Jianguo et al.,1980) and sex-limited races (Huang Junting et al.,1984). Theoretically speaking, all the eggs produced by a single silkworm moth can be masculinized in male nucleus development, but the rate of developed eggs is low and the rate of hatching is even lower. Therefore technically it is still not feasible but only used for theoretical studies; although it is technicallyfeasible to use the balanced lethal systems and the balanced lethal systems have been created with relatively simple manipulation,.it is much laborious in the maintainance of the races, its cost is high and it is difficult to introduce them into the pragmatic races; By using sex-limited normal marking and sex-limited zebra it is simple to identify male and female, and thus can be used for the breeding of seed cocoons, but the sex identification can only be done within the 5* instar when it has already caused some unavoidable loss; although by using the sex-limited mulrilunar system identification of sexes can be done within the 3rd instar, and thus male and female can be reared separately, it has certain negative effects on economic characters. As for the sex-limited cocoon color system, further research has yet to be done. The efficiency of the black and white egg automatic selection by photoelectric means is high but the cost is also high.Since the discovery of the high temperature lethality of the sex-linked chocolate (sch)during its embryonic stage and its sex-linked inheritance (Pan Qingzhong,1992), new horizon has been open for the selective breeding of male silkworm races. Many researches have been done on the silkworm sch.. Lu Cheng et al.(1996) studied the temperature sensitivity of silkworm sch during its incubating stages, and found that the sch gene was closed related with the temperature sensitive lethality; but the problem whether the temperature sensitive lethality was the result of the pleiotropism of sch gene or was determined by another so called lethal gene closely linked to sch, was unsolved. Lin Jianrong (1998) found that the temperature-sensitive trait of sch was determined by a major gene located on the Z chromosome and that it was in a form of sex-linked recessive inheritance. Zhu Yong et al have bred two male silkworm race combinations, namely Qiubai sch X Xiafang and Xiafang X Qiubai sch through introducing the temperature sensitivity of sch to practical race Xiafang and Qiubai; and these two combinations have been in practical tests. Within about 10 years since the discovery the temperature lethality of sch, some practical race combinations for the rear of male silkworm have already been created. Clearly, the temperature sensitivity of sch system has a broad potential for application in the monoculture of male silkworm.However, up...
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