| Diapause is a common physiological phenomenon among insects. To implore the mechanisms of insect diapause, many scholars all over the world have carried on long-term studies. Silkworm is an important economic insect with diapause at its egg stage. In the early 1900's some foreign scholar developed an artificial hatching method by studying the diapause of silkworm eggs, which contributes greatly to the development of sericulture and is still used today. However, many problems about the possible mechanisms of diapause in silkworm remain uncertain. On the basis of previous studies, through experimental morphological, comparative biological and biochemical methods, we studied the physiological metabolic reaction caused by temperature and diapause hormone, the two key factors related to diapause of silkworm eggs in the course of diapause induction, maintenance and termination, especially the changes of lipids, carbohydrate and related enzymes. Combining the results, we established a practical method for long-term storage of hibernated silkworm eggs, which provides important scientific evidence for further clarifying the diapause mechanisms and realizing long-term storage of silkworm eggs.The experiment, in which supraoesophageal ganglions (SG) of the fifth-instar larvae were removed, proved that SG plays an important role in the formation of diapause eggs. When incubated under high temperature (25℃) and light (18-hour light a day) condition, the bivoltive race 781 laid diapause eggs, while with the removal of SG before pupation it laid non-diapause eggs.Quantitative analysis of the lipids in the ovary, the fat body and the blood of pupae with silica gel thin layer chromatography showed that the lipids in the ovary and the fat body had similar composition and consisted mainly of triglyceride, sterol, free aliphatic acids, premium aliphatic alcohol and diglyceride, with triglyceride accounting for about 80% of the total. The lipids in the blood were mainly composed of diglyceride, which accounted for about half the total, followed by sterol and free fatty acids. When SG was removed, the composition of lipids did not vary much, though lipid content changed to some extent with development stages.Gas chromatography analysis indicated that the composition of fatty acids in the ovary, the fat body and the blood of silkworm pupae was similar, the main components being hexadecanoic acid (C16:0), octadecanoic (C18:0), oleic acid (C18:l), linoleic acid (C18:2) and linolenic acid (C18:3). The content of hexadecanoic acid (C16:0) and oleic acid (C18:l) in the ovary and the fat body was about 80% of the total fatty acids. The major fatty acids in the blood were found to be oleic acid (18:1) and linolenic acid (18:3), accounting for about 60%of the total, followed by hexadecanoic acid (16:0). SG removal showed some effects on the content of fatty acids in the ovary, the fat body and the blood, but had no effect on their composition.Triglyceride content in the fat body was as high as 75% at the initial stage of pupation, butdecreased gradually with the development of the pupae. Accordingly, triglyceride content in the ovary was only 20% at the beginning and increased to 64% before eclosion, and the content of diglyceride and free fatty acids in the blood also increased significantly. This suggests that fat in the ovary is transported from the fat body through the blood. SG removal, or diapause hormone shortage, decreased triglyceride and fatty acid content in ovary significantly, while the content of diglyceride and free fatty acids in the fat body and diglyceride in the blood increased, indicating that diapause hormone may promote the transportation of the triglyceride in the fat body into the ovary during silkworm egg formation.The free fatty acid content in the fat body was quite low in the early stage of pupation, and began to increase on the fifth day after pupation. Determined before eclosion, it was about 13% in the control and 18% in the SG removal treatment, thus the latter being significantly highe...
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