Resistance Risk Assessment And Preliminary Study On Resistance Mechanism Of Spodoptera Frugiperda To Tetrachl Orantraniliprole

Spodoptera frugiperda（J.E.Smith）is a major agricultural pest originated from America.After invading Yunnan Province in 2019,S.frugiperda spread rapidly throughout our country,and has led to the serious threat of S.frugiperda to China’s agricultural production.Chemical control is the main measure to control pests,but the susceptibility of S.frugiperda to several insecticides is reduced due to the irrational use of insecticides.Tetrachlorantraniliprole,a new type of diamide insecticide,has excellent control effect on multiple pests,and was recommended for control of S.frugiperda by Ministry of Agriculture and Rural Affairs.It has been reported that the field population of S.frugiperda in China showed 27.8-fold resistance to the diamide insecticide chlorantraniliprole in 2021.Therefore,it is necessary to explore the susceptibility and resistance risk of the field population of S.frugiperda to tetrachlorantraniliprole.In this study,the resistance level of S.frugiperda to tetrachlorantraniliprole was monitored for two consecutive years from 2020 to 2021in the field populations,the resistance risk of S.frugiperda to tetrachlorantraniliprole was further investigated through indoor resistance selection.Furthermore,resistance-related P450 genes were clarified with the selected tetrachlorantraniliprole-resistant strain.The main results are as follows:1.Monitoring of resistance to tetrachlorantraniliprole in field populations of S.frugiperdaFrom 2020 to 2021,the resistance level of 17 field populations of S.frugiperda in Yunnan and Hubei provinces to tetrachlorantraniliprole was monitored using diet surface coating method for two consecutive years.The results showed that the LC₅₀value of tetrachlorantraniliprole to the field populations of S.frugiperda ranged from12.91 mg/L to 85.44 mg/L.Compared with the most susceptible population collected from Wuhan,Hubei（2021-WH）,three field populations（2020-XT,2021-JZ and 2021-ZG）developed low-level resistance to tetrachlorantraniliprole,and the highest resistance ratio was 6.62-fold.The other 14 field populations were susceptible to tetrachlorantraniliprole.The susceptibility of Wuxue,Hubei（2021-WX）population in2021,Jingzhou（2021-JZ）and Zigui（2021-ZG）populations showed a decrease in susceptibility to tetrachlorantraniliprole,with 1.81,2.73 and 2.07-fold resistance ratios,respectively.These results showed that there was a risk of increased resistance to tetrachlorantraniliprole in the field populations of S.frugiperda.2.Risk assessment of resistance to tetrachlorantraniliprole in S.frugiperdaThe resistance of S.frugiperda was selected for 13 consecutive generations through the diet surface coating method.The resistance ratio of S.frugiperda to tetrachlorantraniliprole was 7.45-fold,reaching a low level of resistance.The risk of resistance of S.frugiperda to tetrachlorantraniliprole was evaluated,and the realized heredity of resistance h²was 0.02（the first 10 generations）,it was predicted that tetrachlorantraniliprole was a low-risk insecticide,and tetrachlorantraniliprole could be used as an ideal insecticide for the control of S.frugiperda.3.Effects of tetrachlorantraniliprole with short-term stress on the expression of P450genes in S.frugiperdaThe transcription levels of P450 genes were evaluated by q RT-PCR after exposing the 3^rd instar larvae of S.frugiperda to LC₂₅ and LC₅₀ concentrations of tetrachlorantraniliprole for 24 h,48 h,and 72 h,respectively.The results showed that six P450 genes such as CYP9A59,CYP9A26 and CYP9A31 were significantly up-regulated after exposure to tetrachlorantraniliprole for 24 h,48 h,and 72 h of stress with two doses,indicating that these genes may be involved in the detoxification and metabolism of tetrachlorantraniliprole in S.frugiperda.Furthermore,the expression levels of five CYP3 family genes（CYP9A59,CYP9A26,CYP9A30,CYP9A31 and CYP9A58）in different tissues and developmental stages of S.frugiperda were analyzed by q RT-PCR.It was found that CYP9A59 and other four genes were highly expressed in midgut,pupal and adult of S.frugiperda.CYP9A59 was further selected for RNAi experiment.The results showed that injection of ds CYP9A59 could significantly inhibit the expression of CYP9A59,and led to a significant increase of the susceptibility of S.frugiperda to tetrachlorantraniliprole,which implies that CYP9A59 may be involved in the detoxification metabolism of S.frugiperda to tetrachlorantraniliprole.These studies provide an important theoretical basis for revealing the susceptibility and the mechanism of metabolic resistance of S.frugiperda to tetrachlorantraniliprole.