Effect Of Diet And Temperature On The Growth,Development And Reproduction Of Spodoptera Frugiperda (Smith) (Lepidoptera: Noctuidae)

Spodoptera frugiperda（Smith）（Lepidoptera:Noctuidae）,the fall armyworm,is native to tropical and subtropical America and is an important migratory insect pest.Since it invaded into China by the end of 2018,it had posed a serious threat to maize production in China.Based on the age-stage,two-sex life table,the biological and population parameters of Spodoptera frugiperda fed with 4 kinds of diets were analyzed.Based on the theory of the age-stage,two-sex life table,the biological and population parameters of Spodoptera frugiperda at 6 different temperatures were analyzed.Based on the linear regression method and the direct optimal method,the developmental zeros and effective accumulative temperatures of Spodoptera frugiperda were determined,and the number of generations of different regions in Shandong province was predicted.It was expected to provide a reliable theoretical basis for the monitoring and surveillance and the scientific control of the pest.1.The larvae of Spodoptera frugiperda were fed with Denghai 605 maize leaves,Zhengdan 958 maize leaves,Xinyan 218 maize fresh kernels and artificial diet in the lab.The effects of the 4 kinds of diets on the growth and development and the reproduction of Spodoptera frugiperda were studied,and the population growth dynamics of Spodoptera frugiperda fed with 4 kinds of diets in the next 80d were simulated.The results were as follows:（1）The developmental durations of each stage/instar was determined.（2）The preadult（from egg to pupa）survival rates（s_a）reared on 4 kinds of diets were 0.924 on Denghai 605 leaves,0.875 on fresh maize kernels,0.821 on artificial diet and 0.727 on Zhengdan 958 leaves;The total developmental durations on 4 kinds of diets was 49.00d on Zhengdan 958 leaves,44.17d on Denghai 605 leaves,43.74d on dartificial diet and 43.32d on fresh maize kernels;From high to low,the mean fecundities were 1210.5eggs/female on artificial diet,821.2eggs/female on fresh maize kernels,655.6eggs/female on Denghai 605leaves and 648.8eggs/female on Zhengdan 958 leaves;Pupal weights from high to low were262.95mg on artificial diet,243.37mg on fresh maize kernels,170.59mg on Denghai 605leaves and 199.55mg on Zhengdan 958 leaves.（3）The net reproductive rate（R₀）fed on artificial diet was the highest（484.80offspring/individual）,followed by fresh maize kernels（330.36offspring/individual）,Denghai 605 leaves（285.52offspring/individual）and Zhengdan958 leaves（246.67offspring/individual）;The intrinsic rates of increase（r）on 4 kinds of diets from high to low were 0.1596d^-1on artificial diet,0.1564d^-1on fresh maize kernels and0.1526d^-1on Denghai 605 leaves,and 0.1347d^-1on Zhengdan 958 leaves.The variation trend of the finite rates of increase（λ）on 4 kinds of diets is the same as that of the intrinsic rates of increase（r）.The mean generation time（T）of Zhengdan 958 leaves was the longest（40.84d）,followed by artificial diet（38.72d）,Denghai 605 leaves（37.07d）and fresh maize kernels（37.03d）.（4）The population growth dynamics of Spodoptera frugiperda on 4 kinds of diets in the next 80d were simulated and predicted,the population growth rate on Zhengdan 958leaves was slower than that on the other 3 kinds of diets,and the population size on Zhengdan958 leaves was also lower than on the other 3 kinds of diets.Based on the above results,the fitness of the pest feeding on artificial diet and fresh maize kernels was very high,followed by on Denghai 605 leaves,and the lowest on Zhengdan 958 leaves.2.Six different temperatures（15℃,18℃,21℃,24℃,27℃and 30℃）were selected to study the effects of 6 temperatures on the growth and development and the reproduction of Spodoptera frugiperda fed with fresh maize kernels（Denghai 511）.The results were as follows:（1）The developmental durations of different stages/instars decreased significantly with the increase of temperature in the range of 15℃～30℃.The preadult survival rate（s_a）was the lowest at 15℃（2.7%）,followed by 18℃（48.2%）,and was higher at 21℃～30℃（82.7%～85.6%）.（2）The adults could not mate and reproduce at 15℃;the mean fecundities rose with the increase of temperature,238.45eggs/female at 18℃,784.41eggs/female at 21℃,1003.61eggs/female at 24℃,1048.16eggs/female at 27℃and 1192.84eggs/female at 30℃,respectively.（3）The intrinsic rate of increase（r）and the finite rate of increase（λ）of the moth rose gradually with the increase of temperature at 5 temperatures（18℃～30℃）.The mean generation times（T）shortened significantly with the increase of temperature,and the net reproductive rate（R₀）was the highest at 24℃.（4）The population growth dynamics of Spodoptera frugiperda in the next 90d at 5 temperatures（18℃～30℃）were predicted,the results showed that the population growth rate at 18℃was very slow,and one generation did not complete at 90d;at the other 4 temperatures,the population growth rates accelerated with the increase of temperature,the number of generations increased,and the population sizes were also large.Based on the above results,the temperature range suitable for the growth and development and the reproduction of Spodoptera frugiperda is 24℃～30℃,and the population fitness is high in this temperature range.3.Five different temperatures（18℃,21℃,24℃,27℃and 30℃）were selected to determine the developmental durations of each stage/instar of Spodoptera frugiperda fed with fresh maize kernels（Denghai 511）.According to the relationship between temperatures and developmental rates,developmental zeros and effective accumulative temperatures of each stage/instar of Spodoptera frugiperda were determined by linear regression method and direct optimal method.The developmental zeros and effective accumulative temperatures of the whole generation were 12.72℃and 523.33day·degree by linear regression method,and13.30℃and 497.78day·degree by direct optimal method,respectively.According to the development zeros and effective accumulative temperatures of Spodoptera frugiperda and the monthly average temperatures of the representative regions in Shandong province,the theoretical numbers of generations in five representative regions of Shandong province was calculated.The theoretical numbers of generations of Spodoptera frugiperda in Shandong province were predicted to be 2.5～4.0 generations,including 2.5～3.5 generations in Jiaodong Peninsula,3.0～3.5 generations in Western Shandong,and 3.5～4.0 generations in Central,Southern and Northern Shandong.