Resistance Risk Assessment And Preliminary Study On Detoxification Metabolic Mechanism Of Spodoptera Frugiperda To Indoxacarb

Spodoptera frugiperda（J.E.Smith）（Lepidoptera:Noctuidae）,is a polyphagous and gluttonous migratory pest,which seriously threaten the safe production of maize in China.Up to now,using chemical insecticides is the main method for controlling of fall armyworm.However,it has been reported that S.frugiperda has developed resistance to many kinds of insecticides,and the resistance level is increasing.Indoxacarb is a environmentally friendly oxadiazine insecticide with low toxicity and high efficiency.Indoxacarb can be activated in the lepidopteran insects,and it has been used widely for the control of lepidopteran insect pests.Since the invasion of S.frugiperda to our country in 2019,indoxacarb has been recommended for the emergency control insecticide of S.frugiperda.Therefore,understand the risk of resistance of S.frugiperda and clarify it’s detoxification and metabolism mechanism to Indoxacarb are important for the rational use of indoxacarb.In this study,the risk of resistance S.frugiperda to indoxacarb was evaluated by continuous resistance selection with indoxacarb,and the molecular resistance mechanism of S.frugiperda to indoxacarb was preliminarily explored by using resistant and susceptible strains.The main results are as follows:1.The selection of susceptible and resistance strain of Spodoptera frugiperda to indoxacarb and the evaluation of the risk of resistance S.frugiperda to indoxacarb.Laboratory resistant（WXR）and relatively susceptible strain（XNS）of S.frugiperda to indoxacarb were selected by diet-overlay method.By successive selection with indoxacarb for 10 generations,a indoxacarb resistant strain was obtained,with resistant ratio of 29.40-fold,and the LC₅₀ value of the strain is 60.27 mg/L.The results of resistance risk assessment showed that the h² of the indoxacarb resistant strain was 0.091,indicating that the S.frugiperda has a relative low risk of resistance to indoxacarb.Cross-resistance assay indicated that the indoxacarb-resistant strain（WXR）showed negative cross-resistance to spinetoram,and no obvious cross-resistance to chlorantraniliprole,lufenuron,chlorfenapyr,emamectin benzoate,tetrachlorantraniliprole or lambda-cyhalothrin.2.Detoxification metabolic biochemistry mechanism of Spodoptera frugiperda to indoxacarbThe results of synergism bioassays of the laboratory resistant strain（WXR）,field resistant strain（HG）and relatively susceptible strain（XNS）of S.frugiperda showed that DEM could significantly increase the susceptibility of laboratory resistant strain（WXR）and field resistant strain（HG）of S.frugiperda to indoxacarb,and the synergistic ratio of DEM in two resistant strains were 2.72 and 1.69,respectively.However,PBO and TPP exhibited no significant synergism to indoxacarb.Furthermore,assay of detoxification enzyme activities showed that the activity of glutathione S-transferase（GSTs）was significantly higher in the indoxacarb resistant strains than that of the relatively susceptible strain.These results suggested that the enhanced activity of glutathione S-transferase（GSTs）might be an important resistance mechanism of S.frugiperda to indoxacarb.3.The identification and functional verification of GSTs genes in S.frugiperda involved in indoxacarb resistance.A total of 40 GSTs genes were identified in S.frugiperda,and phylogenetic analysis showed that these 40 GSTs genes were distributed in 4 GSTs subfamilies.q RT-PCR results showed that 15 of the 40 GSTs genes were significantly up-regulated both in the laboratory selected resistant（WXR）and field resistant（HG）strains compared with the relatively susceptible strain（XNS）,among which GST31 and GST32 showed a remarkable higher expression in the WXR with 218.68-fold and 135.90-fold increase,respectively.RNAi results showed that silencing of GST31 significantly increased the susceptibility of resistant S.frugiperda to indoxacarb,suggesting that the overexpression of GST31 gene may play an important role in the development of S.frugiperda resistance to indoxacarb.These studies provided a scientific basis for rational use of indoxacarb,and laid a foundation for further revealing the detoxification metabolic mechanism of S.frugiperda to indoxacarb.