| Diapause is a characteristic phenomenon in insects to adapt to complex and variable or adverse environmental conditions so as to reproduce and develop their populations in nature. Polymorphism of diapause is only known in population of wheat blossom midges. It is the diapause polymorphism that makes the pests overcome themselves live drawbacks such as few generations (1 generation a year generally), small size of individual, low rate of reproduction and very faint living of adult and cause serious disaster with occasional, regional and uneven dumpling characteristics. On the basis of looking up and reading lots of literatures, this paper summarized and reviewed systematically the history and current status of diapause researches in insect in eight respects as follows: elemental concept about diapause; types of diapause; induction, maintenance and termination of diapause; relationships between diapause and environment conditions; changes of organ structure in diapause insects; diapause features in physiology and biochemistry; regulation mechanism of diapause as well as hereditary evolution of diapause. The advance of diapause researches in the wheat blossom midge, Sitodiplosis mosellana (Gehin) was yet summarized and reviewed in six respects including bionomics features; mechanisms of induction, maintenance and termination; morphological characteristics; physiological features; changes of chemical substances in diapause larvae and divisions of diapause status in China. Modern analysis methods of chemical substances and polyacrylamide gum electrophoresis (PAGE) of protein and isozyme were firstly used to study changes of main chemical substances and isozymes in diapause larvae of 5". mosellana in different periods or status. The main results are as follows:1. Obvious difference in contents of main chemical substances was not discovered inlarvae with various diapause years. Contents of total carbohydrate, glycerine, protein, RNA and DNA in larvae diapausing for 1 year or 2 years were estimated respectively. Results showed that there were not remarkable differences in content of the five chemical substances in larvae with various diapause years. It suggested that energy consumption of S. mosellana should be very economical during diapause. It might be one of important causes that the larvae of S. mosellana could pupate and emerge after 12 years of continuous diapause in soil although their size of individual is very small.2. Non-cocooned larvae and cocooned larvae were different in appearance, but diapause essence of them was identical. The content of main chemical substances in both non-cocooned larvae and cocooned larvae was compared. The remarkable difference between non-cocooned larvae and cocooned larvae collected at the same time of various seasons was not discovered in the content of total carbohydrate, glycogen, protein, RNA and DNA. Therefore, there was of the same diapause essence and feature in both non-cocooned larvae and cocooned larvae as the seasonal change. A fault opinion that non-cocooned larvae were used to be thought as status of diapause and cocooned larvae as status of non-diapause was corrected.3. Seasonal changes of main chemical substances displayed the quantitative features of diapause level in S. mosellana. There was remarkable difference in contents of total carbohydrate, trehalose, glycogen, glycerine, free amino acid, protein, RNA and DNA as well as main fatty acids in larvae of S. mosellana in different seasons. The contents of total carbohydrate, glycerine, free amino acid in larvae was increasing in both summer and winter and decreasing in both autumn and spring. On the contrary, the contents of protein and RNA displayed a different trend. There was more obvious change in contents of chemical substances in spring. Therefore, diapause level in larvae of S. mosellana was changed as environmental conditions and seasons changed or there were different levels of diapause in various individuals. It was proved to be possible that parts of larvae pupated and emerged...
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