It has been known that cocoon shells in some white cocoon races of the silkworm emit fluorescence under UV-light. To identify the fluorescence of white cocoon shells, three-dimensional (3-D) fluorescence analysis was carried out. In the 3-D spectra of the cocoon shells emitting yellowish fluorescence under black light, we found two fluorescence peaks (peak α at an excitation wavelength of 335 nm and an emission wavelength of 420 nm; peak β at an excitation wavelength of 370 nm and an emission wavelength of 540 nm). Fluorescence peak β disappeared by washing the cocoon shells with 70% hot aqueous methanolic solution and the peak was very similar to the fluorescence peak of quercetin 5, 4´-di-O-glucoside, strongly suggesting that the yellowish fluorescence in white cocoon shells was due to quercetin 5, 4´-di-O-glucoside or its related compound(s). On the other hand, fluorescence peak α which remained after the treatment was very similar to the fluorescence peak of standard silk fabric, showing that the fluorescence in white cocoon shells resulted from the silk protein itself. In addition, we found that the average value of fluorescence intensity of peak β in cocoon shells of Chinese original races is much stronger than that in cocoon shells of Japanese original races, which may reflect the difference of genetic background involved in white cocoon traits between Chinese and Japanese races.

 Several studies have attempted to cryopreserve fertilized eggs of the silkworm, Bombyx mori. However, the results of those studies showed no larvae hatched, or none of the hatched larvae ate feed and they died at the first instar. Specifically, the hatchability of permeabilized eggs was lower than that of dechorionated eggs, suggesting that the cryoprotectant did not penetrate the permeabilized eggs. We therefore investigated methods for promoting the permeation of exogenous substances into silkworm eggs. To maximize the potential for effectively permeating exogenous substances through the chorion into eggs, we treated eggs with a permeabilization solution containing 2.5% sodium hypochlorite and 1% Tween 80 and estimated the effect of treatment on hatchability. The results showed that treatment of the eggs for five minutes had markedly higher hatchability than eggs treated for six minutes. Secondly, permeation of an exogenous substance, Rhodamine B, was tested using eggs treated with the permeabilization solution. Observation under fluorescent light revealed that the permeation of Rhodamine B into the egg treated for five minutes. Observation of the treated eggs by scanning electron microscopy revealed structural changes to the chorion, which was considered to have affected the change in permeability. In conclusion, we demonstrated that exogenous substances can permeate into eggs treated with the experimental permeabilization solution. It is considered that treatment with the permeabilization solution will not only be useful for studies on cryopreservation, but also induction experiments using physiologically active substances into silkworm eggs.

 The effects of long-term periods of silkworm breeding with repeated selections for suitability to Japanese kimonos might extend not only the main components of cocoon shells and raw silk but also to the feel of silk fabrics. In the present study, we investigated and analyzed soluble properties of glutinous substances of cocoon shells of 575 silkworm races maintained and owned by the National Agriculture and Food Research Organization, NARO. Based on the elution amount of glutinous substances per 1 gram of cocoon shell, the solubility of the glutinous substances at each boiling time for the cocoon shell was analyzed by Steel-Dwass test. As a result, the glutinous substances of cocoon shells dissolved drastically within 30 minutes, and then, the elution became slow with a time-dependent curve over the boiling. Based on this property, we adopted 30-min boiling for the cocoon shell to estimate solubility of the glutinous substances of cocoon shells of NARO's 575 races and revealed that there are geographical and race differences among the silkworms in the solubility. Our results would be useful for screening the silkworms for future breeding in the production of silkworm race-specific raw silk.