Development of long-term preservation is essential for conservation of stocks of silkworm genetic resources. Thus far, a few methods have been reported, but more improvement is required for practical use. We have developed two effective modifications of a method for long-term preservation using frozen ovaries. One was slow cooling (1. °C per min) until -80. °C of the donor ovaries made possible by use of a BICELL freezing vessel. Using donor ovaries of 4th instar larvae, the average number of eggs laid per moth increased significantly from 110.7. ±. 53.4 eggs per moth by slow cooling with the BICELL vessel vs 12.3. ±. 10.3 eggs per moth by direct cooling in liquid nitrogen. A second improvement was connecting the thread bodies of the donor ovaries with those of the host in the transplantation step. Females operated on with the new method yielded a significantly higher percentage of moths that laid fertilized eggs than those transplanted with the standard procedure (70.4. ±. 21.6% vs 22.9. ±. 9.3%).
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