Resistance Monitoring And Risk Assessment Of Sulfoxaflor In Nilaparvata Lugens (St(?)l)

Nilaparvata lugens(St(?)l),the brown planthopper(BPH)is a monophagous pest of regional importance that only feeds on the phloem of rice in Asia.It is mainly found in the southern part,south-western part,middle and downstream areas of Yangtze River and Jianghuai area in China every year and has great impact on good quality and high production of rice in China.Chemical control still remains the most practical way to suppress N.lugens populations,but frequent and wide use of synthetic insecticides controlling N.lugens had led to the development of insecticide resistance.As a result,it is of great importance to know the resistance levels among different geographical populations to commonly used insecticides and to guide the rational use of insecticides in the field and resistance management.The research was aimed at knowing resistance levels of brown plant hoppers to different insecticides by monitoring resistance among different geographical populations;At the same time,the susceptibility of N.lugens to sulfoxaflor and resistance risk in N.lugens to sulfoxaflor were studied,which could provide a theoretical basis of resistance management and also ensure to control N.lugens scientifically.The main results are as follows:1.Resistance monitoring to conventional insecticides in brown planthopper.In order to know the resistance status of brown planthopper to insecticides at present which facilitates the use of insecticides on brown plant hopper scientifically,resistance monitoring of brown plant hopper from different regions to seven insecticides was carried out in 2013 and 2014 using rice stem dipping method.The results are as followed:All populations tested from 2013 to 2014 are at moderate to high levels of resistance to pymetrozine.While the resistant level had a downward trend in 2014 compared with that of 2013(67.1?312.9 fold in 2013,47.0?243.1 fold in 2014).Only Danyang population increased dramatically in 2014(243.1 fold);For the neonicotinoid insecticides thiamethoxam,the resistance ratios of field populations further increased compared with 2013 except Nantong populations(decreased from 44.5 fold to 28.5 fold).In addition to the population from Lujiang which developed low level of resistance(5.3 fold)in 2014 to nitenpyram,other populations were all susceptibility to decreased susceptibility to nitenpyram(0.3?3.5 fold)and no significant difference was found between the years;for the 13 field populations in 2014 represented 0.7-8.3 fold of resistance to dinotefuran compared with the susceptible population;Based on LC50 values,the resistance in populations from different regions to buprofezin showed significant increase from 2013 to 2014;The results of the organophosphorus insecticide chlorpyrifos also exhibited an obvious increase in resistance over the 2-year period.In addition to Nanning population(74.8 fold),others from 2013 is sensitive to low levels of resistance(1.4?8.7 fold)developed to low to moderate levels of resistance in 2014(6.6?34.9 fold);Populations from Xiaogan,Jinshan,Gaocun,Taihe,Jinhua in 2014 reached medium level of resistance to flufiprole,while others were susceptibility to low level of resistance.As for buprofezin,the brown planthopper populations which were monitored in two years all showed medium to high level(134.6?499.0 fold).High resistance level still kept to imidacloprid(132.3?1615.5 fold).2.Baseline susceptibility of N.lugens to sulfoxaflor and assessment of resistance risk in N.lugens to sulfoxaflorBaseline susceptibility of N.lugens to sulfoxaflor was determined using the rice-stem dipping method.The results showed that LC50 value of the susceptible strain to sulfoxaflor was 0.491 mg/L,and the 13 field populations represented 0.5-5.9 fold of resistance compared with the susceptible population in 2014.Among these populations,Shanghai and Fuqing populations developed low levels of resistance to sulfoxaflor;then a field-population of N.lugens collected from Jinhua in Zhejiang Province was selected after repeated exposure to sulfoxaflor to determine the risk of resistance evolution.After 10 generations of selection,there was an increase from 0.542 mg/L to 1.756 mg/L in LC50.The realized heritability(h2)of resistance was estimated as 0.1667 by using threshold trait analysis.The projected rate of resistance evolution indicated that if h2=0.1667,b(slope)=3.3353 and 70%-90%of the population was killed at each generation,and then a 10-fold increase in LC50 would be expected in 12-18 generations for sulfoxaflor.These results show that the risk of resistance development exists in N.lugens to sulfoxaflor after continuous application.