Resistance Monitoring And Preliminary Study Of The Resistance Mechanisms Of Spodoptera Frugiperda To Chlorantraniliprole

The fall armyworm,Spodoptera frugiperda（J.E.Smith）（Lepidoptera:Noctuidae）,is a major migratory agricultural pest worldwide.S.frugiperda has great damage ability to crops and the invasion of S.frugiperda seriously threatens the safe production of major food crops in China.Currently,the control of S.frugiperda mainly relies on the application of chemical insecticides,but the insecticide resistance of S.frugiperda has become increasingly prominent due to the overuse of chemical insecticides.Chlorantraniliprole is a novel diamide insecticide that shows high toxicity and control efficacy to lepidopteran insect pests.In 2022,chlorantraniliprole has been registered for the control of S.frugiperda in China.Elucidating the resistance risk,resistance status,and the potential resistance mechanisms of S.frugiperda to chlorantraniliprole have great significance for the efficient prevention and control of S.frugiperda.Therefore,we monitored the field resistance levels of S.frugiperda to eight widely used insecticides,and determined the resistance risk of S.frugiperda to chlorantraniliprole by resistance selection.Moreover,the potential resistance mechanisms of S.frugiperda to chlorantraniliprole was studied in this study.The main results of this research are as follows:1.The susceptibilities of six field populations of S.frugiperda collected from two provinces of China to eight insecticides were determined using the diet-overlay method.The results showed that all field populations of S.frugiperda are still sensitive to emamectin benzoate,spinetoram,lufenuron,indoxacarb,and chlorfenapyr,while some field populations of S.frugiperda had developed low levels of resistance to chlorantraniliprole,tetrachlorantraniliprole,and lambda-cyhalothrin.2.A chlorantraniliprole-resistant strain of S.frugiperda was established in the laboratory by continuous selection with chlorantraniliprole for 10 generations using the diet-overlay method.This resistant strain has evolved 16.97-fold resistance to chlorantraniliprole compared with the susceptible strain and 3.27-fold resistance compared with the original strain（F₀）.The realized heritability（h²）of resistance to chlorantraniliprole in S.frugiperda was estimated as 0.10,suggesting that there is a moderate risk of resistance to chlorantraniliprole.The results of cross-resistance demonstrated that the chlorantraniliprole-resistant strain developed positive cross-resistance to lufenuron（CR=2.57-fold）and tetrachlorantraniliprole（CR=2.83-fold）,negative cross-resistance to spinetoram（CR=0.65-fold）.However,there is no significant cross-resistance to other four insecticides（emamectin benzoate,chlorfenapyr,lambda-cyhalothrin,indoxacarb）.3.The results of the synergist bioassay showed that PBO significantly increased the toxicity of chlorantraniliprole to S.frugiperda by 2.54-fold in the resistant strain,and the detoxification enzyme activity assays results showed that the activity of cytochrome P450monooxygenases was significantly higher in the chlorantraniliprole-resistant strain compared to the susceptible strain.These results indicated that the P450 may play a key role in the evolution of resistance of S.frugiperda to chlorantraniliprole.To determine which P450 genes may be associated with chlorantraniliprole in S.frugiperda,the relative expression levels of P450 genes were analyzed in the susceptible and resistant strains by q RT-PCR.The result indicated that the expression levels of twenty-six P450 genes were significantly upregulated in the resistant strain than that in the susceptible strain,among which CYP4L13 showed a notably high expression level with a 31.69-fold change.Furthermore,RNAi experiments demonstrated that silencing of the expression of CYP4L13can significantly recover the sensitivity of the resistant strain to chlorantraniliprole,indicating that CYP4L13 could play a very important role in the resistance of S.frugiperda to chlorantraniliprole.