Sublethal Effects Of Tetraniliprole On Experimental Population Of Spodoptera Frugiperda (Lepidoptera:Noctuidae)

Spodoptera frugiperda is a major transnational migratory agricultural pest with strong adaptability,high fecundity and gluttony.In December 2018,S.frugiperda invaded China for the first time and spread rapidly,causing great damage on South China’s agricultural production.Chongqing is located in the transition zone of S.frugiperda.Monitoring,early forecast,effective prevention and control are the keys to prevent the northward migration of S.frugiperda.In this study,the dynamics of the occurrence of S.frugiperda in Chongqing in 2020 were investigated and their haploid types was identified.Taking the experimental population of S.frugiperda as major object,based on the toxicity selection of six insecticides including tetraniliprole,spinetoram,chlorantraniliprole,pyridalyl,chromafenozide and triflumezopyrim,the sublethal effect of tetraniliprole on S.frugiperda was evaluated.The effects of sublethal concentrations at LC₁₀ and LC₃₀ on population survival,growth and reproduction were analyzed using age-stage,two sex life table analysis and the population dynamics were predicted based on life-table parameters in the next 60 days by Timing model.The activity of carboxylesterase,glutathione S-transferase and mixed-function oxidases were measured under the sublethal concentration.The main research results were as follows:1.Investigation and haplotype identification of S.frugiperda in ChongqingSystematic monitoring and field investigation on S.frugiperda population were conducted in Chongqing in 2020,S.frugiperda was first detected corn fields in Beibei and sorghum fields in Yongchuan in early May.Subsequently,it was found in 7 counties including Qianjiang,Hechuan,Youyang,Tongliang,Liangping,Jiangjin in late May.It spread to 19 counties including Wansheng and Tongnan in early July to late August,showing a trend of spreading from south to north.The genetic characteristics of the collected S.frugiperda samples were compared with COI and Tpi molecular marker genes.According to the results marked by COI gene,there were two haploid types,17 out of 72 samples were"maize type"and 55were"rice type",with the"rice type"being the dominant.According to the 10differential haplotype loci of Tpi gene,the 65 amplified samples showed three different haplotypes at the third and fourth sites.including 33 samples of maize haplotype（AT）,17 samples of rice haplotype（GA）,and 15 samples of heterozygous（AT/GA）.According to the number of different haplotype loci,all samples belonged to"maize type".Because these two molecular markers are different in gene location,their results differed to some extent,however,considering the differences of host types in the trapping sites of S.frugiperda,Tpi molecular markers are more consistent with the haplotype identification of S.frugiperda in Chongqing2.Toxicity test of six insecticides to S.frugiperdaToxicity of six insecticides were tested on the 3^rd instar of S.frugiperda by leaf immersion method Results showed that the toxicity of 200 g/L tetraniliprole SC was the highest,10%triflumezopyrim SC was the lowest,with LC₅₀ values after 48h were0.0031 mg/L and 156.02 mg/L,respectively The order of insecticide toxicity from high to low was as follows:200 g/L tetraniliprole SC>60g/L spinetoram SC>200 g/L chlorantraniliprole SC>10.5%pyridalyl EC>5%chromafenozide SC>10%triflumezopyrim SC.According to the toxicity test results,200 g/L tetraniliprole SC was selected for the following test.3.Sublethal effects of tetraniliprole on the F₀ and F₁ generation of S.frugiperdaIn order to investigate the sublethal effects of tetraniliprole on survival,growth and reproduction of S.frugiperda,age-stage,two sex life table were constructed under LC₁₀and LC₃₀.Results showed that,compared with the control,the developmental duration of the 4^th to 6^th instar larvae of F₀ and the developmental duration of larvae of F₁generation was significantly prolonged.The pupal stage and pre-oviposition stage of F₀and F₁ generations as well as the adult lifespan of F₁ generation were significantly prolonged.The average pupal weight of F₀ generation increased significantly.The egg hatching rate was significantly decreased.Meanwhile,there was no significant difference in the average spawning quantity of F₀ generation.However,in F₁ generation,the average fecundity of LC₃₀ treatment group was 948.71 eggs,which was significantly reduced compared with 1197.62 eggs of the control group.While the average fecundity of S.frugiperda under LC₁₀ was 1032.63 eggs,which was not significantly different from control.The r_m andλof F₁ generation in LC₁₀and LC₃₀treatment groups were significantly decreased.Although R₀ and GRR were also decreased,but there was no significant difference.Meanwhile,the average generation time（T）and population doubling time（D_t）were significantly prolonged.The population dynamics within 60 days starting from 10 fertilized eggs were predicted based on the simulation of population parameters by Timing model.Results showed that,compared with the control,the population growth rate of S.frugiperda treated with sublethal concentration of tetraniliprole was slower and the population number increased dramatically.4.Detoxification enzyme activity of S.frugiperda under tetraniliprole treatmentIn order to determine the effects of sublethal concentration of tetraniliprole on detoxification enzymes activity of S.frugiperda,the activities of carboxylesterase,glutathione S-transferase and mixed-function oxidases in the 3^rd instar of S.frugiperda treated with sublethal concentration of tetraniliprole at 12,24,36,48 and 72 h were determined.The results showed that,in 72 h,the carboxylesterase（Car E）was increased first and then induced;the overall activity of glutathione S-transferase（GST）was increased.However the activity of mixed-function oxidases（MFO）was not significantly changed.It is speculated that Car E and GST may be involved in the formation of resistance to tetraniliprole in S.frugiperda.In conclusion,this study investigated and haplotypely identificated S.frugiperda in Chongqing,and illumination the sublethal effect of tetraniliprole on population growth and characters of S.frugiperda.This stuty provided a theoretical basis for the mornitering and sustainable management of S.frugiperda in the transition zones.