Resistance Monitoring And Risk Assessment Of Triflumezopyrim In Brown Planthopper,Nilaparvata Lugens(ST(?)L)

As a migratory pest widely distributed in Asia,the brown planthopper,Nilaparvata lugens(Stal),could cause disaster lost on rice yield in China.Chemical insecticides mainly used to control the brown planthopper for decades and developed resistance because of long-term abuse and overuse.Therefore,it is necessary to monitor the resistance status of the brown planthopper populations to conventional insecticides in China and evaluation the resistance risk of new insecticide,so as to provide suggestion on candidate insecticides which could be applied on control the brown planthopper in paddy and design the preventive resistance management on triflumezopyrim.1.Resistance monitoring of brown planthopperIn order to clarify the status of the resistance of the brown planthopper to conventional insecticides in China,the the rice-stem dipping method was used to monitor the resistance of field populations collected from nine provinces in China in 2017-2018.The monitoring results showed that about 75%of the brown planthopper populations reached high resistance level to pymetrozine.To dinotefuran,except for high resistance level(RR=139.5)was detected in Shanghai Jinshan population in 2017,other monitored populations of brown planthopper showed moderate resistance level,Resistance ratio were 24.3-69.5 folds in 2017 and 23.6-93.0 folds in 2018.Most of the brown planthopper populations were low to moderate resistance to nitenpyram(RR=4.6-15.5),and the change of resistance was not obvious during 2 years.Except for the low resistance level of the brown planthopper population in Tengchong Yunnan in 2018,other monitored populations reached moderate resistance level(RR=8.8-26.1)to sulfoxaflor.To chlorpyrifos,most of populations were moderate resistance level(RR=12.8-43.7),except for the low resistance level(RR=9.3)appeared in the Shanggao Jiangxi population in 2018.All monitored populations still kept high level of resistance(RR=185.8-219.6)to thiamethoxam in 2017,and a decrease in 2018(RR=51.6-219.2).To other 2 stopping used insecticides,high level of resistance to the buprofezin and imidacloprid were still observed,and there is no significant changes with that of previous years.2.The sensitivity monitoring and assessment of resistance risk in brown planthopper to triflumezopyrimTriflumezopyrim is novel insecticide that could effectively control rice planthoppers and registed in China in 2017.In order to better study the efficacy of trifluoropyrim on brown planthopper,the sensitivity of the brown planthopper population collected from the main rice producing area of the Yangtze River region in China was monitored by rice-stem dipping method in 2017-2018.It was found that most of the brown planthopper populations were still susceptible in these two years,except the populations of Ningdu in Jiangxi province and Nanning in Guangxi province showed low resistance levels in 2018,the resistance ratio were 5.3-fold and 6.1-fold,respectively.In order to better predict the development of resistance of the trifluoropyrim,the brown planthopper treated with trifluoropyrim 15 generations continuously in labratory.the field population of brown planthopper collected from Yancheng,Jiangsu province in 2017 was used as original one.After screened continuously for 15 generations,LC50 increased from 0.11 mg/L to 0.542 mg/L,and the resistance ratio increased from 1.7 to 8.5 folds.The h2 of triflumezopyrim resistance using threshold trait analysis was 0.0774 in the whole stage of selection,and h2 was 0.1230 in the stage(F1-F10)of selection.As the selection continues,it was likely that the resistance of N.lugens to triflumezopyrim would increase further.The rate of resistance development is directly related to h2 and selection intensity.For example,when the h2=0.0776 and the selection mortality is 50%at each generation,the resistance ratio increases 10-fold require 30.2 generations.Moreover if the h2=0.0780 and 90%mortality was selected,the LC50 of N.lugens can be increased by 10-fold to triflumezopyrim only require 13.2 generations.In short,it is recommended that triflumezopyrim or nitenpyram combined with pymetrozine could be used to control brown planthopper,and dinotefuran,sulfoxaflor and chlorpyrifos also could be used as alternate insecticides.Continue stopping imidacloprid,buprofezin and thiamethoxam to control N.lugens,and pay more attention on the resistance development of these insecticides.