Resistance Monitoring To Insecticides In Sogatella Furcifera (Horvath) And Resistance Risk Assessment To Dinotefuran

The white-backed planthopper Sogatella furcifera(Horvath)is a major long-distance migratory pest of rice in Asia,occurred in main rice planting area of China every year.The white-backed planthopper has great impact on good quality and high production of rice by direct sap-sucking and as plant virus vectors.Chemical control is still a major measure for controlling S.furcifera.So we evaluated the resistance status of several insecticides including chlorpyrifos,imidacloprid,thiamethoxam,buprofezin and pymetrozine in S.furcifera collected from the main rice-growing area in China during 2013 and 2014.While the resistance problem of planthoppers growing by reason of long-term,widely and irrational use of the pesticides.It is difficult to find the ideal chemicals when the S.furcifera and N.lugens mixing occurs,especially the efficient insecticides applied in rice paddies are becoming less and less.Dinotefuran has an especially high insecticidal activity against a wide range of hemipterous insects with low mammalian toxicity was defined as a third-generation neonicotinoid and exhibited no obvious cross-resistance to other insecticides.It is considered that dinotefuran will replace imidacloprid to become a new generation neonicotinoid for widespread controlling sap-sucking pest.The production and consumption of dinotefuran will increase in China as patents expire in 2014.So it is very necessary to monitor the resistance and assess the resistance risk of dinotefuran.In the meantime,in order to guide the scientific and rational field application and delay the resistance development of this chemical,we conducted the research on cross-resistance and co-toxicity with dinotefuran in planthoppers.1.The resistance monitoring of S.furcifera to commonly used insecticidesThe resistance of S.furcifera collected from Jiangsu Province,Zhejiang Province,Yunnan Province,Jiangxi Province,Sichuan Province and Anhui Province,were monitored by seedling dipping method during 2013 to 2014.The results indicated that all the populations kept susceptible to thiamethoxam(0.8 to 2.0-fold).All monitored populations were susceptible or minor resistance to imidacloprid(1.8 to 4.4-fold)except Jinhua population(5.8-fold).Gaochun population deveploed high level resistance to chlorpyrifos(127.6-fold)in 2013 and the remainder were in moderate level resistance(23.8-88.2-fold)during the past two years.All the tested populations exhibited medium resistance to buprofezin except Jinhua and Jiaxing,These two populations showed high level resistance to buprofezin in 2014.Moreover,all the populations kept susceptible to medium resistance to pymetrozine(10.0 to 28.1-fold)in 2014 and Gaochun pupolation was the highest one.The resistances of 12 field populations of S.furcifera collected in China were monitored by seedling dipping method during 2013 to 2014.The results showed that all the populations kept susceptible to dinotefuran(0.6-to 1.3-fold)in the two years.2.The cross-resistance of five insecticides to dinotefuran in rice planthoppersThe data of the study on cross-resistance of five insecticides to dinotefuran indicated that the populations of L.striatellus showed medium resistance to chlorpyrifos and fipronil exhibited no obvious cross-resistance to dinotefura.The strains of S.furcifera exhibited medium resistance to chlorpyrifos and buprofezin respectively showed no cross-resistance to dinotefuran.In the meantime we have not found the cross-resistance to dinotefuran from the Jinhua populations of N.lugens which demonstrated high resistance to imidacloprid and medium resistance to thiamethoxam.Besides that,a resistant strain get from laboratory selection showed high resistance to buprofezin exhibited no cross-resistance to dinotefura.3.Assess the resistance risk of dinotefuran in S.furcifera and N.lugensContinuous selection with dinotefuran on S.furcifera and N.lugens populations collected from Hangzhou in 1995 and Hexian in 2013 respectively.Under laboratory condition,the resistance levels were raised 2.0-fold and 5.0-fold for S.furcifera and N.lugens with realized heritability(h2)of 0.0515 and 0.0959 after 19 and 15 generations of selections respectively.Compared with the susceptible strains,the selected strains of S.furcifera and N.lugens showed medium resistance and low resistance to dinotefuran with the LC50 value increasing to 2.341 mg/L and 2.432mg/L respectively.The projected rate of resistance evolution indicated that a tenfold increase in LC50 would be expected in 21 and 10 generations for S.furcifera and N.lugens respectively if 90%of the population was killed at each generation.It suggested that the two rice planthoppers have the definite risk of resistance to dinotefuran and N.lugens had higher resistance risk than S.furcifera.4.The co-toxicity of dinotefuran mixed with five insecticides for controlling S.furciferaThe co-toxicity of dinotefuran mixed with chlorpyrifos,isoprocarb,ethofenprox,buprofezin and sulfoxaflor at different ratios against the 3rd instar nymph of S.furcifera were determined.The results showed that dinotefuran with 5 insecticides in suitable mixing ratios had relatively high co-toxicity against S.furcifera by the co-toxicity coefficient method.Among them,significant synergism was detected in the mixture of dinotefuran and ethofenprox at the ratio of 1:20 showing the highest synergism with CTC was 417.1;Secondarily dinotefuran and isoprocarb at the ratio of 1:5,the CTC was 416.6.Dinotefuran and chlorpyrifos at the ratio of 1:3,the CTC was 337.7.The synergistic effects of the three kinds of above-mentioned combinations were remarkable.