Effects Of Different Diets On The Growth, Development, Energy And Flight Ability Of The Fall Armywor

Spodoptera frugiperda（J.E.Smith）,which belongs Lepidoptera and Noctuidae,is a major migratory agricultural pest in the world.It has the characteristics of wide distribution,many hosts,strong ability of migration and strong ability of reproduction.It invaded China in 2019,and then quickly diffused many provinces and cities,which posed a serious threat to the production of corn,rice,wheat and other food crops in China.In this study,we tested the cannibalism behavior of S.frugiperda,and investigated the growth and development,energy substances,flight ability and intestinal microbial diversity of five different diets.The main results were summarized as follows:1.Cannibalism rate of S.frugiperda and its predation number on young larvaeThe cannibalism rate of the 1st to 6th instar larvae of S.frugiperda was measured under different densities（10,20,30,40）.The results showed that the cannibalism rate of larvae increased at first and then decreased with the increase of instar,and reached the peak at the age of 5.In this study,the daily feeding amount of the 3rd to 6th instar larvae on the 2nd larvae of different densities and the 4th to 6th instar larvae on the 3rd larvae of different densities were observed under laboratory conditions.At the same time,the feeding behavior of the older larvae of S.frugiperda to the young larvae was analyzed from the point of view of functional response.The results showed that the functional response of the 3rd to 6th instar larvae to the 2nd larvae and the 4th to 6th instar larvae to the 3rd larvae fitted well with the Holling II mode.The maximum feeding amount of the 3rd to 6th instar larvae on the 2nd instar larvae were 76.47,85.70,117.92 and 96.05respectively,and the maximum feeding amount of the 4th to 6th instar larvae on the 3rd instar larvae were 38.83,59.49,and 58.87 respectively.The feeding amount of the older larvae to the younger larvae increased with the increase of the density of the younger larvae,and the amount of feeding decreases with the increase of the state of prey.The results of this experiment laid a theoretical foundation for understanding the interspecific cannibalistic behavior of S.frugiperda larvae.2.The Effects of different diets on the growth,development and reproduction of S.frugiperdaThe growth and development,survival and reproduction of S.frugiperda were measured after feeding on corn,corn+larvae,rice,peanut and Curcuma wenyujin.The results showed that when S.frugiperda was fed with corn+larvae,the mean generation time（T）was shorter than that fed with corn only.The preadult survival rate,fecundity,net reproductive rate（R₀）and intrinsic rate of increase（r）were lower than those of S.frugiperda fed with corn leaves only,indicating that the host adaptability of S.frugiperda decreased after preying on conspecific larvae.The adaptability of S.frugiperda fed on Curcuma wenyujin was the lowest and its mean generation time（T）was the longest（40.19 d）,while the intrinsic growth rate（r）,net reproductive rate（R₀）,fecundity and finite rate of increase（λ）were the lowest.3.The Effects of different diets on the energy substances of larvae and adults of S.frugiperdaBy measuring the energy substance of larvae and adults of S.frugiperda fed on four kinds of food,it was found that the effect of diet on glycogen content of larvae was in the following order:corn+larvae（7.97 mg/g）>corn（5.59 mg/g）>peanut（5.34mg/g）>rice（4.11 mg/g）.The order of trehalose content in larvae was corn+larva（31.93mg/m L）>corn（22.33 mg/m L）>peanut（20.08 mg/m L）>rice（10.47 mg/m L）.There was no significant difference in triglyceride content in larvae of S.frugiperda fed on four diets,while the protein concentration of peanut was the highest（6.31 g/L）and that of corn and larvae was the lowest（4.27 g/L）.For adults,the contents of glycogen,trehalose and protein in both male and female adults were the highest when they were fed on corn+larvae,and the lowest in rice.The triglyceride content of both male and female adults fed on corn+larvae was the highest,while peanut was the lowest.There were also significant differences in energy substances between male and female adults who ate the same diets,glycogen and triglyceride showed that male>female,while trehalose and protein showed female>male.This study is helpful to further reveal the nutritional relationship between S.frugiperda and host plants.4.The Effects of different diets on the flight ability of S.frugiperdaThe flight distance,flight duration and flight velocity of male and female adults of S.frugiperda reared with corn+larvae,corn,rice and peanut were measured by flight mill device.The results showed that when S.frugiperda fed on corn+larvae,the longest flight distance could reach 20.62 km and the longest flight time could reach 9.02 h within 12 h flight testing.Among the four kinds of food,the flight ability of adults fed on corn+larvae were the strongest,followed by corn,and the overall flight ability of S.frugiperda fed on peanuts and rice was poor.The flight ability of S.frugiperda was also different within different genders who ate the same food.On the whole,the flight ability of males was slightly stronger than that of females,but the difference was small.This study showed that S.frugiperda has strong flight ability,and there are differences in flight ability between male and female adults fed on different diets and the same diet,which provides a scientific basis for the diffusion ability of S.frugiperda.It laid a theoretical foundation for elucidating the migration system of S.frugiperda and Lepidoptera pests.5.The Effects of host plants on the intestinal bacterial diversity of S.frugiperdaThe intestinal bacterial diversity of S.frugiperda fed on corn and rice was compared by Illumina Hi Seq high-throughput sequencing technique.The results showed that the intestinal bacterial richness decreased significantly after the corn-fed larvae were transferred to rice.Based on the analysis of the intestinal bacterial species distribution of S.frugiperda larvae feeding on corn and rice,it was found that at the phylum level,the dominant intestinal flora of corn-fed larvae was Proteobacteria,with a relative abundance of 47.50%.Firmicutes was the second dominant flora,and the relative abundance was 39.33%.On the other hand,the dominant flora of feeding rice was Firmicutes,with a relative abundance of 74.13%,and Proteobacteria was the second dominant flora,with a relative abundance of 22.00%.At the genus level,the dominant intestinal flora of S.frugiperda larvae feeding on corn was Enterobacter,accounting for 39.01%,while that of rice was Enterococcus,accounting for 41.90%.KEGG function prediction showed that intestinal bacteria of S.frugiperda fed on corn and rice played an important role in carbohydrate metabolism,amino acid metabolism and membrane transport.This study laid a theoretical foundation for the study of the interaction mechanism between host plants and insect intestinal bacteria,and also provides a new perspective for the scientific prevention and control of pests.