The Mechanism Of Early Resistance Evolution To Triflumezopyrim In Nilaparvata Lugens

The brown planthopper?BPH?,Nilaparvata lugens?St?l?is an important pest on rice.The long-term irrational use of insecticides has led to a severe situation of resistance to BPH.It has been reported that BPH produced varying degrees of resistance to 33 active ingredients of insecticides.Triflumezopyrim is a novel meionic insecticide developed by Du Pont company of the United States,acting on nicotinic acetylcholine receptors.In 2017,it was officially registered in China to control Planthopper.In this study,resistance of BPH was monitored to triflumezopyrim in different field populations in paddy fields.Besides,triflumezopyrim resistance strain was selected to study the resistance risk assessment and the resistance mechanism of BPH to triflumezopyrim.The main findings are as follows:1. Monitoring of the sensitivity of BPH to triflumezopyrimThe rice seedlings dipping method was used to monitor the sensitivity of 41geographical populations of BPH in 10 provinces to triflumezopyrim in 2016-2019.The results showed that the resistance ratio of 39 field populations to triflumezopyrim were all less than 5 compared to the susceptible strain,except for the Henan Xinyang-2016population and the Anhui Hefei-2016 population.Therefore,currect BPH field populations in China still remain sensitive to triflumezopyrim.2. Determination of the cross-resistance spectrum between triflumezopyrim and other insecticidesTaking the indoor susceptible strain as the initial strain,a resistant strain with the same genetic background as the susceptible strain was obtained with resistance ratio of 200 after30 generations consecutive resistance selection to triflumezopyrim.In the selection process of triflumezopyrim resistance,the sensitivity of the BPH strain at different resistance levels to other insecticides was determined by rice seedling dipping method,and the triflumezopyrim,nitenpyram,clothianidin,cycloxaprid,etofenprox and chlorpyrifos pose a potential risk of cross-resistance,and there is no risk of cross-resistance with imidacloprid,thiamethoxam,dinotefuran,sulfoxaflor and isoprocarb.Through the hybridization and backcrossing of the resistant and susceptible strains,bioassay results were used to draw LD-P lines for genetic analysis of resistance.The results showed that the resistance of BPH to triflumezopyrim was inherited by a co-dominant inheritance controlled by autosomal multiple genes.Using the bisexual life table to systematically analyze the age development period,instar survival rate,adult lifespan and other parameters of the BPH triflumezopyrim resistant and susceptible strains.The results showed that resistant strains at 1^st,2^nd,3^rd,and 4^th nymphs development periods and total pre-oviposition period?TPOP?were significantly prolonged,and the lifespan of BPH was significantly shortened.There was no difference in the 5^th nymphs development periods and adult pre-oviposition period?APOP?.The single female spawning volume and egg hatching rate were significantly reduced.The intrinsic growth rate?ri?,weekly growth rate???,and net appreciation rate?R₀?of the resistant strain were significantly reduced,and the average generation cycle?T?was significantly extended.The relative fitness of the resistant strain was 0.62 for susceptible strains.Therefore,the triflumezopyrim resistant strain has a significant fitness cost.3. Resistance bio-chemical mechanism of BPH resistance to triflumezopyrimThe study of biochemical mechanism of the resistance of BPH to triflumezopyrim showed that the inhibitors PBO,DEM,and TPP significantly increased the sensitivity of BPH to triflumezopyrim,with synergistic ratio of 6.0,1.6,and 1.7,respectively.Fluorescence quantitative PCR technique was used to determine the relative expression of detoxification enzyme genes in the resistant and susceptible strains of BPH.The detoxification enzyme genes that played a major role in the resistance of BPH to triflumezopyrim were identified,of which Car E-7 is up-regulated by more than 300 times.The results indicate that Car E-7,a carboxylesterase gene,may mediate the resistance of BPH to triflumezopyrim.