| Spodoptera litura Fabricius (Lepidoptera:Noctuidae) is a worldwide polyphagous insect pest that attacks the plant up to 209 species of host plant in 99 families. In recent years a marked increase in the frequency of outbreaks, the outbreak area has expanded each year and it is becoming more and more serious damage to agricultural production and has caused serious losses.The fecundity of S. litura is strong. Single female lays eggs up to about 2000.It outbreak easily in a short period of time. Host plants are a important factor which affect the fecundity of S. litura. In the final analysis, host plants influence the fecundity of S. litura by affecting the hormones in the body which regulate their development, but also by affecting the changes of soluble protein synthesis in their reproductive system directly.Therefore, to study influence and the mechanism of different host plants on the fecundity of S. litura is of important theoretical and practical significance for clarifying the inherent mechanism of harm of an outbreak of S. litura.In this study, based on the degree of preference of S. litura to host plant, by feeding on different host plants (cabbage, cotton, potato, soybean, cowpea, alligator weed) indoors to observe the development of S. litura, we studied the growth, development, fecundity, female and male reproductive system development, the changes of soluble protein content in the genital mutilation, as well as the changes of the ecdysone and juvenile hormone in different developmental stages of S. litura. This experiment also involved the study on the nutrients in the leaves of different host plants, and the discussion on the mechanism of different host plants on the fecundity of S. litura. The main conclusions are as follows:1.Different host plants affected the fecundity of S. litura significantly. And that, it was the same general trend which different host plants influenced on the realised fecundity, the potential fecundity (the potential fecundity= the realized fecundity+ residual eegs in the abdomen) and output rate of S. litura. This study showed that feeding on different host plants, the realized and potential fecundity of S. litura were the size of the order: cabbage> Cotton> potato> soybean> cowpea> alligator weed. Fed on cabbage which is one of the most preferred host plants, S. litura's fecundity was also largest. The realized fecundity, the potential fecundity and the output rate were largest, respectively 1561.23, 1596.08 and 97.50%.Whereas,the number of the residual eggs in the abdomen is the least, only 34.85. Fed on alligator weed which is the disliked host plant, the fecundity of S. litura was smallest. The realized fecundity, the potential fecundity and the output rate were smallest, respectively 537.57, 692.08 and 77.48%. Whereas the number of the residual eggs in the abdomen is the largest, with an average of 156.50.The realized fecundity of S. litura which fed on cabbage is 3 times than that fed on alligator weed, and the potential fecundity is about 2.3 times. This shows that fed on the prefer host plants, the fecundity of S. litura in general is also relatively stronger.2.There was a significant impact of different host plants on the growth and development of reproductive organs of S. litura. Fed on different host plants, the ovary of female, the length and fresh weight of the male accessory gland of the1-day-old male and 3-day-old non-mated male, the fresh weight of the spermary of male were in the same trends, the order of as follows: cabbage> cotton> potato> soybean> cowpea> alligator weed. This study found that fed on the prefer host plants including cabbage, cotton, potato, the development of the reproductive organs were better which is of great significance to the fecundity of S. litura.3.There was a significant effect of different host plants on the synthesis of soluble protein in the reproductive system of S. litura. We tested the content of soluble protein in the reproductive system in different stages of S. litura, including 1 day, 3 days, 3 days after mated. It showed that when fed on cabbage, cotton, potato, the content of soluble protein of S. litura was higher. However when fed on soybean, cowpea, hollow philoxeroides, the content was lower.4.We tested the titers of MH and JH at different stages of S. litura through HPLC method. It illuminated that the titer of MH in the haemolymph of the 6th larvae of S. litura was significantly higher when fed on soybean and cotton than those fed on other host plants. The content is lowest when fed on cabbage. The titer of MH in the adult of S. litura falls down so sharply that it has been unable to be detected using HPLC method. Influence of different host plants on the JH in 6th larvae and adult of S. litura was significant. It showed that the titers of JH in 6th larvae fed on cabbage and cotton were higher significantly than those fed on other host plants. After eclosion to adult, the titers of JH in the female adult falled down significantly, however the male didn't significantly. In female adult, the titers of JHâ…¡were higher when fed on cabbage and cotton, however lower when fed on cowpea and alligator weed. In the male adult,the changes in the content of JHâ…¡are basically in the same trends. The titers of JHâ…¡in the male adult of S. litura fed on cabbage,cotton and sweet potato were higher significantly than those fed on soybean, cowpea and alligator weed.5.There are significant differences in primary nutrient content in leaves of different host plants. The abundance of primary nutrient content is higher in the leavers of cabbage, cotton and sweet potato than that in soybean, cowpea and alligator weed.6.In order to identify the relationship between fecundity influencing factors which are sub-factors and fecundity factors which are generating factors, they were studied with grey relational analysis. The result showed that the content of JHâ…¡in S. litura, soluble sugar and nitrogen content in host plant leaves were closely related with the realized fecundity, potential fecundity, output rates, and pupal weight. The contents of JHâ…¡, soluble sugar and nitrogen were the most effective factors for the fecundity of S. litura. There were less influence of the content of MH in S. litura and water in leaves on the fecundity of S. litura. It can speculate that different host plants influence the fecundity of S. litura through the following way: as a result of significant differences in primary nutrient content such as soluble sugar and nitrogen in leaves of different host plants, the titers of MH and JH in S. litura changed after the larvae were fed on different host plants leaves, which affected the development and the synthesis of soluble protein of the reproductive system of S. litura. The final result of the changes was that the fecundity of S. litura was different after the larvae were fed on different host plants.
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