| Plutellda xylostella L.mainly harms cruciferous vegetables.P.xylostella has strong reproductive ability,short life cycle,and more generations.It is distributed around the world and is a worldwide pest.In agriculture,chemical control is the mainstay.Due to the large amount of the same kind of pesticides used throughout the year,the resistance of P.xylostella has developed rapidly,and it is difficult to prevent and control.The cultivation of cruciferous vegetables in Tibet is large,and the occurrence of P.xylostella is common and serious,but the degree of resistance to P.xylostella is not yet clear.In this study,the leaf dipping method was used to determine the resistance of commonly used pesticides to P.xylostella field populations in 6 locations in Tibet,and three synergists,diethyl maleate,synergistic ether and triphenyl phosphate,were used.Indoor toxicity testing with abamectin so that pesticides can exert their best effects.Based on the results of drug resistance determination,a reasonable combination with synergistic effect was screened out through the experiment of mixing two different agents.This study clarified the current status of resistance to commonly used pesticides in 6 locations in Tibet,and developed a reasonable and feasible strategy for preventing and controlling P.xylostella in the field,thereby reducing the excessive use of pesticides,and providing a theoretical basis for the better effectiveness of pesticides.The main findings are as follows:(1)The abamectin and fenvalerate in P.xylostella populations at six locations in Xietongmen County,Tibet,Tibet Agricultural and Animal Husbandry College,Shigatse City,Nyingchi Town,Milin County,Lhasa City were determined by leaf dipping method The degree of resistance of five agents:pyrethrin,imidacloprid,clothianidin,lambda-cypermethrin.The results showed that the resistance of the P.xylostella populations in the six locations to the five pesticides commonly used in production practice varied.The farm population of Tibet Agricultural and Animal Husbandry College,Xietongmen County,Nyingchi Town,Lhasa City,Milin County P.xylostella field populations have high levels of resistance to fenvalerate.The resistance of P.xylostella field populations to Fenvalerate in Xigaze was extremely high,with a resistance multiple of 224.872 times.The level of amine resistance showed a decrease in sensitivity.The resistance to clothianidin in the remaining four locations was all low-level resistance;the resistance to imidacloprid,the population of the farm practice base,was low-level resistance,15.178 times,Xie Tongmen The population in the county,Shigatse City,Milin County,Nyingchi Town,and Lhasa City is moderately resistant;the resistance to lambda-cypermethrin is high in Xigaze City,Xietongmen County,and Milin County.The populations in the town and Lhasa showed moderate resistance;the populations of P.xylostella field populations in 4 locations in Linzhi Town,Milin County,Xietongmen County and Xigaze City were all at a high level of resistance to avermectin The population is at a medium resistance level.(2)Determination of three kinds of synergist and insecticide avermectin,diethyl maleate(DEM),synergistic ether(PBO)and triphenyl phosphate(TPP)in the field population of P.xylostella on the farm practice base of Tibet Agricultural and Animal Husbandry College After the compounding,the synergistic effect selects the optimal compounding ratio combination of the ideal synergist.The test results show that: when avermectin is mixed with diethyl maleate(DEM),when the active ingredient ratio is 1:1,the toxic effect ratio is the largest 2.08,and it has obvious synergistic effect and synergistic multiple up to 2.53.Avermectin is mixed with triphenyl phosphate(TPP)and synergistic ether(PBO)respectively.When the effective ingredient ratio is 1:5,the toxic effect ratio is the highest and both are 2.00.When the ratio of avermectin to PBO active ingredient is 1:5,the synergistic effect on P.xylostella larvae is not obvious,and the synergistic ratio is only 1.01.(3)Fenvalerate insecticides with a high level of resistance in P.xylostella field populations in 6 locations were mixed with 3 other insecticides(thiamethoxam,imidacloprid,and lambda cypermethrin)to Tibet Agricultural and Animal Husbandry College.The field toxicity of P.xylostella in the farm practice base was tested for joint virulence,and the combination with synergistic effect was initially selected and further screened to find the optimal combination ratio of the two pesticides.The test results showed that the toxicity of each treatment group to P.xylostella after the mixing of Fenvalerate and Imidacloprid showed an additive effect.Fenvalerate and lambda cypermethrin were mixed,and the treatment group(2)(5)(effective ingredient content was 1273.324 +34.646,848.882 + 138.584)showed an additive effect on the third instar larvae of P.xylostella,and the remaining 9 treatments all exhibited an antagonistic effect.When fenvalerate was mixed with clothianidin,the four treatment groups(4)(6)(9)(10)(the content of active ingredients were 990.363 + 50.473,707.402 +84.122,282.961 + 134.595,141.480 + 151.420),these four treatment groups all performed on the third instar larvae of P.xylostella For synergy,the co-toxic factors are 81.69,60.15,67.74,and 86.89,respectively.Among them,fenvalerate+clothianidin(141.480 + 151.420),fenvalerate+clothianidin(282.961+ 134.595)were more effective for the P.xylostella field population,and the co-toxicity coefficients were: 126.23,130.25. |
