Study On The Efficacy And Sublethal Effect Of Broflanilide On Spodoptera Frugiperda

The fall armyworm Spodoptera frugiperda（Smith,1797）,native to the Americas,is widely distributed and seriously harmful.Its larvae have strong gluttony and polyphagia,and can feed on more than 350 kinds of hosts,which directly threatens the world’s food production.Since the invasion of Spodoptera frugiperda into China in 2019,it also poses a serious threat to the yield of corn and other food crops.Broflanilide,as an m-diamide or m-benzoylaminobenzamide insecticide,has a novel mechanism of action,is environmentally friendly,and has a good effect on Spodoptera frugiperda.At present,there is a lack of research on the detoxification and metabolism mechanism and sublethal effect of Broflanilide on Spodoptera frugiperda.In this paper,10 kinds of insecticides,including Broflanilide,and the control effects of Broflanilide and two kinds of pesticides on corn Spodoptera frugiperda were compared and studied;At the same time,the effects of sublethal doses of Broflanilide on the growth,development,reproduction and detoxification metabolism of Spodoptera frugiperda were studied.The results of the study are as follows:（1）The indoor virulence and field control effect of 10 insecticides including Broflanilide against Spodoptera frugiperda larvae were determined by leaf dipping method and spraying method,respectively.The results of the indoor toxicity test showed that the insecticides with higher toxicity to Spodoptera frugiperda were in the order of Emamectin benzoate>Flubendiamide>Broflanilide>Chlorantraniliprole>Cyantraniliprole>Thiotraniliprole>Tetraniliprole>Lambda-cyhalothrin>Indoxacarb>Thiosultap monosiltap.The field efficacy test results showed that:7 days after the treatment,the control efficacy of the 10 tested insecticide preparations against Spodoptera frugiperda larvae in descending order was 5.7%Emamectin benzoate DF>20%Flubendiamide WG>10%Thiotraniliprole SC>100 g/L Broflanilide SC>20%Chlorantraniliprole SC>10%Cyantraniliprole OD>18%Tetraniliprole SC>150 g/L Indoxacarb EC>25 g/L Lambda-cyhalothrin EW>90%Thiosultap monosiltap SP.It can be seen that Emamectin benzoate and diamide insecticides have good control effects on corn Spodoptera frugiperda,and can be recommended for the control of Spodoptera frugiperda in corn fields.（2）The screened results of compound formula of Broflanilide,Lambda-cyhalothrin and Emamectin benzoate show that:The optimum mass ratio of Broflanilide and Lambda-cyhalothrin is 7:3;The synergistic effect was the most obvious when the mass ratio of Broflanilide and Emamectin benzoate was 1:9.The field efficacy test of the compounding agent was carried out with each optimal ratio,and the results showed that:7 days after the treatment,the control effect of Broflanilide and Lambda-cyhalothrin mixed with medium and high concentrations can reach more than 95%.The control effects of the three doses of Broflanilide mixed with Emamectin benzoate all reached more than 96%.Greater or significantly greater than the control efficacy of the two single agents.（3）The response of Spodoptera frugiperda on different hosts to pesticides and the sub-lethal effect of Broflanilide on Spodoptera frugiperda on different hosts were studied.The indoor virulence of Broflanilide against three different hosts of Spodoptera frugiperda was determined by spot method.The results showed that the LD₅₀ value was the highest in the treatment of feeding corn（0.499 mg/L）,followed by the treatment of feeding soybean（0.472mg/L）,and the treatment of feeding peanut（0.389 mg/L）,Prove that the corn Spodoptera frugiperda has the strongest resistance to pesticides;Two sub-lethal doses were selected to treat the test insects to study the sub-lethal effect of Broflanilide on different hosts of Spodoptera frugiperda.The results showed that Spodoptera frugiperda can complete the development of generations on corn,peanut and soybean;Spodoptera frugiperda feeding on corn has the shortest growth cycle and the strongest reproductive ability;The higher the experimental dose,the greater the gap between the biological indicators of the three host populations compared with the blank control.（4）The activities of detoxification enzymes and protective enzymes of Spodoptera frugiperda were measured,which treated by sub-lethal effect dosage(LD₁₅ and LD₃₀)and lethal medium concentration of 50%percent(LD₅₀)of Broflanilide.The results revealed that the activity of detoxification enzymes increased with the increase of dosage.The specific activities of GST and EST were positively correlated with the treatment concentration.The GST activity reached the maximum under the stress of LD₅₀.The specific activity of GST in all treatments was significantly higher than that in the control group.The EST activity was significantly higher than that of the control group,which was 1.38 times,under stress of LD₅₀.The MFO activity increased with the increase of treatment concentration.The specific activity of MFO in the LD₃₀ dosage treatment group was the highest,which was 1.33 times higher than that in the control group.However,the activity of MFO enzyme in LD₅₀treatment group decreased,and there was no significant difference between LD₅₀ treatment group and the control group.The specific activities of the three protective enzymes increased first and then decreased with the increase of treatment dosage.There was no significant difference in SOD activity in each treatment group compared with the control group.And under the stress of LD₃₀,its specific activity was the highest,which was 1.03 times that of the control group.The specific activities of POD and CAT in LD₃₀ group were 1.34 times and 1.35 times of control group,respectively,which were significantly higher than those in control group.The ratio activity of two protective enzymes in the LD₅₀ treatment group decreased,but was still higher than that in the control group,but there was no significant difference.In conclusion,Broflanilide has a good control efficiency on Spodoptera frugiperda,and the compound with beta-cyhalothrin and Emamectin respectively has synergistic effects.The biological fitness of Spodoptera frugiperda fed on corn was the strongest under sublethal dose stress.The treatment dosage of LD₁₅,LD₃₀ and LD₅₀ can all induce the activities of detoxification and protective enzymes in Spodoptera frugiperda,suggested that they play a role in the resistance of Spodoptera frugiperda to Broflanilide.These results can optimize the field application strategy of Broflanilide in the control of Spodoptera frugiperda,and lay a foundation for the study of the resistance of Spodoptera frugiperda to Broflanilide.