| The fall armyworm,Spodoptera frugiperda(J.E.Smith)(Lepidoptera:Noctuidae)is a transboundary migratory pest native to the tropical and subtropical Americas.After invading China in 2019,it quickly spread to most parts of the country,seriously threatening economic crops such as corn and wheat.Changes in plant nutrients such as protein and carbohydrates are one of the main reasons that affect the growth,development,reproduction and outbreak of insects.Understanding the relationship between protein,carbohydrate content and the population dynamics of S.frugiperda is helpful for effective pest control strategy.In this study,the basic nutritional protein and carbohydrate intaken by S.frugiperda larvae is the object.The basic nutritional content of two varieties of maize was measured to facilitate the configuration of an artificial diet.Then,on the basis of artificial diet,by changing the ratio of protein and carbohydrates,the effects of different nutrient ratios on the feeding,development,reproduction and nutritional physiology of S.frugiperda were explored around its nutritional regulation mechanism,and the reasons for its rapid reproduction were understood from the perspective of nutrition.The main results are as follows:1.Nutritional structure and dynamics of two varieties of maizeThe variation trend of water content in leaf,stalk and ear of two maize cultivars Suyu waxy 5 and Yue sweet 16 was different at different ages.The water content of the Yue sweet 16 stalk(917.1 mg/g)was significantly higher than that of the other five groups of samples.The dynamic trend of crude fat content in different tissues of the two maize varieties was different,and the content of leaf was significantly higher than that of stalk.Protein and carbohydrates are the most important nutrients in plant tissues.The dynamic trend of protein content in different tissues of the two maize varieties was relatively stable,and there was no significant difference in each measurement period.The dynamic trend of free amino acid and carbohydrate content in different tissues of the two maize varieties was inconsistent,and the content in ear was significantly higher than that in other tissues.2.Effects of two maize varieties on the development and reproduction of S.frugiperdaS.frugiperda were reared with leaves of two maize varieties,Suyu waxy 5 and Yue sweet 16,respectively,and there was no significant difference in larval developmental period and survival rate.The pupa weight of the population that fed on the leaves of Suyu waxy 5 maize was larger.The male pupae were heavier than the female pupae in the two populations,and there was no significant difference in the sex ratio by the Chi-square test.Adult biological parameters such as oviposition period,fecundity and longevity were not significantly different.The net reproductive rate,intrinsic rate of increase,finite rate of increase and generation time of the population fed with the Suyu waxy 5 leaves were higher than those of the Yue sweet16 population,but there was no significant difference.The results showed that the suitability of S.frugiperda to Suyu waxy 5 maize was higher than that of Yue sweet16 maize.3.Effects of protein and carbohydrates on growth,development and physiology of S.frugiperdaA total of 11 artificial diets with different protein(p)and carbohydrate(c)ratios of 3 types were set up,and the developmental period,survival rate,pupa weight and adult fecundity of S.frugiperda reared on different p:c artificial diets were recorded.At the same time,the storage capacity of soluble protein and soluble sugar as well as the supercooling point and freezing point of the 4th,5th and 6th instar larvae and the3 rd pupae were measured.The S.frugiperda fed on artificial diets with constant protein content but a gradient of increased carbohydrate content(p20:c36,p20:c40,p20:c44,and p20:c48),and larvae in the p20:c48 treatment group could not complete the larval stage.When the S.frugiperda larvae fed on a constant carbohydrate content and the protein content increases(p26:c20,p30:c20,p34:c20 and p38:c20)or when the total protein and carbohydrate content remains at 50%(p24:p26,p32:c18 and p40:c10)artificial diet,larvae can develop smoothly to adults.There was significant difference in the content of soluble protein and soluble sugar,freezing point and subcooling point in different growth stages of S.frugiperda fed with different p:c artificial diet.The results showed that excessive content of protein and carbohydrate in artificial diets affected the development,survival and reproduction of S.frugiperda,especially excessive carbohydrate content could cause S.frugiperda unable to complete the whole life cycle.The p32:c18 artificial diet was the most suitable protein and carbohydrate ratio for S.frugiperda larvae.4.Geometric Framework(GF)model in 6th instar larvae of S.frugiperdaArtificial diets with 3 concentrations(30%,42% and 54% of total pc)and 5proportions(p3:c1,p2:c1,p1:c1,p1:c2 and p1:c3)were set.To determine the compromise rules and protein and carbohydrate intake of S.frugiperda 6th instar larvae feeding on the 1st and 2nd-3rd days.On different feeding days,the female and male larvae of S.frugiperda(identified after pupation)were fed with artificial diets with different pc totals.The nutritional compromise rules were the Close distance rule(CD rule),but there are difference in the nutrient intake arrays.The larvae of S.frugiperda fed with the pc total amount 54% artificial diet on the 1st day and the 42%artificial diet on the 2nd-3rd day had the largest food intake.At the same feeding time,the food intake amount of female and male larvae on artificial diet with the same concentration and proportion was different.In addition,the total food intake,weight gain and feed conversion rate of the 6th instar larvae of S.frugiperda were different when they were fed the artificial diets with different concentration and proportion.This study understands the reasons for the growth,development and reproduction of S.frugiperda from a nutritional point of view,provides a basis for in-depth research on nutritional ecology and the development of effective control strategies of S.frugiperda,and can also provide reference for other insect nutrition regulation mechanisms. |
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