| Diapause and seasonal polymorphism are two important adaptive strategies for insects to deal with the change of external environment. Sericinus montelus Gray is endemic in south-east Asia, and it is one of the rare butterfly species in China. Research on its adaptive strategies will contribute to protection and scientific utilization of this valuable species. Preliminary studies reported that S. montelus Gray nymphs emerged either as spring or summer morph adults under different photoperiod and temperature conditions in the laboratory, and these two morphs of adults were different in some morphological characteristics. However, whether this seasonal polymorphism exists under natural conditions and whether the variation pattern of morphological characteristics is continuous or discontinuous are unclear. Preliminary results also showed that S. montelus Gray overwintered as diapausing pupae, and its diapause could be affected by temperature and photoperiod. However, the biochemical mechanism of diapause of this species has not been studied. In this research, specimen of wild population of Sericinus montelus Gray in Changsha city were collected, and area of forewing and hind wing, relative area of red spot in forewing and hind wing, relative area of fantail in hindwing were caculated using automatic computer aided design software, in order to provide an accurate standard to distinguish spring morph and summer morph of this speices. Meanwhile, contents of total sugar, rehalose, glycogen, total protein, total fat, and glycerol in diapause and non-dispause pupae were measured at the different development phase, so as to preliminary explore the biochemical basis of diapause in S. Montelus, provide a basis to explain the formation mechanism of its spring morph and summer morph.The main results were as follows:1. Forewing and hindwing area of the spring morph females were significantly smaller than that of the summer morph females. Among generations of summer morph, forewing and hindwing area of females in the first and second generation were close, but both of them were significantly smaller in females of the third, fourth and fifth generation. Fantail length was shorter and relative area of fantail was smaller in spring morph females than in summer morph females, and no significantly difference in length and relative area of fantail existed among different generations of summer morph. However, area of red spot in forewing of the spring morph females was significantly greater than that of the summer morph females. These results indicated that forewing and hindwing area, red spot area in forewing, and fantail of female S. montelus exhibited seasonal dimorphism.2. Similar with females, forewing and hindwing area of the spring morph males were significantly smaller than that of the summer morph males, and forewing and hindwing area of females in the first and second generation of summer morph were close, but both of them were significantly smaller in males of the third, fourth and fifth generation; fantail length was shorter and relative area of fantail was smaller in spring morph males than in summer morph males, and no significantly difference in length and relative area of fantail existed among different generations of summer morph; area of red spot in forewing of the spring morph males was significantly greater than that of the summer morph males. These results indicated that forewing and hindwing area, red spot area in forewing, and fantail also were important indexes for distinguish between the spring and summer morph of male S. montelus. However, relative area of red spots in hind-wing and red spot in annal angle was significantly greater in the spring morph males than in the summer morph males, suggesting that seasonal polymorphism of S. montelus were different between sexes.3. Total sugar content of diapausing pupae was significantly greater than that of non-diapausing pupae in S. montelus Gray at the first day. In addition, no significantly difference of total sugar content was observed in diapausing pupae of different age in 15 d, but total sugar content of non-diapausing pupae decreased during this period. This result indicated that total sugar content of S. montelus Gray was affected by the state of diapause, and sugar was the main energy material in S. montelus Gray diapausing pupae. Comparisons of glycogen and trehalose content between diapausing and non-diapausing pupae of S. montelus showed that the glycogen content of diapause pupae was significantly greater than that of non-diapausing pupae, but trehalose content was similar in both diapausing pupae and non-diapausing pupae. It was suggested this species belong to glycogen accumulation.4. Comparison of protein content of diapausing pupae and non-diapausing pupae showed that the protein content of diapause and non- diapause were higher at first day of pupation, and decreased in the first 10 d, suggesting that diapause may not correlated with protein in S. montelus. However, protein content of non-diapausing pupae was significantly greater than that of diapausing pupae at the 15th day. This may be due to the fact that cell division of non-diapausing pupae is highly active at this stage, requiring lots of protein to build a variety of tissues and organs.5. According to the examination of fat and glycerol content of diapausing and non-diapausing pupae, the fat content of diapause was significantly higher in non-diapausing pupae than in diapausing pupae at the first day, and no significant difference of glycerol content existed between these two kinds of pupaes, suggesting that lipid was not the energy storage material for diapause. However, fat content increased in diapausing pupae but decreased in non-diapausing pupae as the growing days. It seems that diapausing pupae may need to accumulate fat for improvement of cold resistance. This inference needs to be further tested. |
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