| The beet armyworm Spodoptera exigua(Lepidoptera: Noctuidae)is a significantly polyphagous agricultural pest.At present,S.exigua has become major pest on vegetables,flowers and cotton in the Yangtze River basin,the southern provinces and regions of China.For a long time,using insecticide has been the major strategy to control S.exigua,but the resistance has become a difficulty of its control.Therefore,it is necessary to monitor the resistance status and provide strategies for scientifical control and resistance management.In the current study,we monitored the resistance status of field population to 11 insecticides,and valuated the control effect of the 8 insecticides,screening the synergistic formula of insecticide and insecticide synergistic agent,which provided theoretical basis for scientific control and resistance management of the S.exigua.The main results are as follows:1.Resistance monitoring in Spodoptera exiguaOn the basis of establishing a baseline of susceptibility to 11 insecticides,the resistance to 11 insecticides in populations of Baiyun Guangzhou,Huangpi Wuhan,Chongming Shanghai and Jieshou Fuyang was monitored by leaf immersion method.The results showed that the 4 populations of S.exigua are susceptibility to spinosad and methomyl,low and morderate levels of resistance to methoxyfenozide,chlorfenapyr and indoxacarb,morderate levels to chlorpyrifos,morderate and high levels to chlorfluazuron,chlorantraniliprole and tolfenpyrad,and high levels to emamectin benzoate and betacypermethrin.2.Field efficacy test of 8 insecticidesThe field efficacy test of 8 insecticides resistance to S.exigua was implemented on the natural population of Huangpi Wuhan.The results showed that the control effect of chlorfenapyr on S.exigua was better at the present stage,and the control effect of chlorfenapyr on S.exigua was more than 70% and the highest was more than 90%.Chlorfluazuron,methoxyfenozide and indoxacarb had the highest control efficacy of more than 80%.The highest control efficacy of chlorantraniliprole and tolfenpyrad was over 70%.The control effect of beta-cypermethrin and emamectin benzoate on S.exigua was lower than 50% per day after treating with single insecticides.3.Insecticide synergistic formula screeningThe synerergism formulas and optimum ratio of the selected insecticide combination were selected by means of the mutual dedermination and co-toxicity index.The results showed that the ratio of chlorfenapyr and beta-cypermethrin at 7:3～12:1 had synergistic effect,the three combinations of 7:3,9:1 and 11:1 were selected for field efficacy test.Compared with single insecticides,three combinations of the same dosage(50 g/667 m2)and high dosage(67 g/667 m2)improved the control effect per day after three combinations treatments,and low dosage(33 g/667 m2)improved the control effect per day after treating with two combinations,except the combination of 9:1.After 3 days,7days and 10 days,the control effect of 7:3 and 11:1 decreased slightly,but there was no significant difference.According to the above results,the ratio of chlorfenapyr and betacypermethrin at 7:3～12:1(Ratio of active components 1.21:1～6.24:1)has synergistic effect on the control of S.exigua.4.Screening of insecticidal synergistThe activities of multifunctional oxidase,glutathione S-transferase and carboxylesterase were detected in sensitive population and four field populations of S.exigua in Baiyun Guangzhou,Huangpi Wuhan,Chongming Shanghai and Jieshou Fuyang.The results showed that the activities of multifunctional oxidase in four field populations were significantly higher than those in sensitive populations.The activity of glutathione S-transferase in Chongming Shanghai population was significantly higher than that in sensitive population,and the activity of carboxylesterase in Jieshou Fuyang population was significantly higher than that in sensitive population.Pepper butyl ether(PBO),an inhibitor of multifunctional oxidase,was selected as insecticidal synergist.The results showed that PBO had obvious synergistic effect on beta-cypermethrin,chlorantrantranamide and emamectin.The results of pot experiment showed that PBO had the most obvious synergistic effect on beta-cypermethrin,and had a little synergistic effect on emamectin benzoate and chlorantranamide.In summary,this study clarified the resistance level of 11 insecticides in the main occurrence areas of S.exigua.The results of single insecticide screen showed that chlorfenapyr had a higher control effect on S.exigua in the field.The combination ratio of chlorfenapyr and beta-cypermethrin in 7:3 to 12:1had synergistic effect on S.exigua.We next found that piperonylbutoxide had synergistic effect on beta-cypermethrin,emamectin benzoate and chlorantraniliprole.The results provided theoretical basis and technical support for scientific control and resistance management of S.exigua. |
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