| The brown planthopper(hereinafter called BPH),Nilaparvata lugens(St(?)l) is one of the most important insect pests to rice crop.In resent years,population of this pest and its damage to rice inceased dramatically in our country,and the control effect of imidacloprid on this pest in field decreased significantly,so it is necessary to study the susceptibility or resistance to several kinds of pesticides in BPH in order to control this pest effectively in field.The susceptibility to 24 insecticides was evaluated by rice stem dipping method in field populations of BPH collected from Guangxi province(Nanning GXNN and Guilin GXGL),Huan province(Changde HNCD) and Jiangsu province(Jiangpu JSJP) in 2005, and another population(S) which is susceptible to imidacloprid reared in laboratory.The result showed that the toxicity of fipronil was the highest among 24 pesticides;the toxicity of thiamethoxam,buprofezin and nitenpyram was only the next to fipronil;acetamiprid, chlopyrifos and isoprocarb had relatively low toxicity;While promecarb,silafluofen, BPMC,ethofenprox,carbosulfan,MTMC,dimethacab,methamidophos,triazophos, arprocarb,imidacloprid,dimethoate and DDVP had low toxicity;malathion,cycloprothrin and fenoxycarb had the lowest toxicity to BPH.All of these insecticides,imidaclothiz showed dramatically different toxicity in the five populations.The recommended pesticides to control BPH in rice field were fipronil,thiamethoxam,buprofezin,chlorpyrifos, isoprocarb and DDVP.Resistance monitoring to buprofezin was determined by rice stem dipping method in BPH collected from twenty-six field populations of eight provinces(region) in China during 2005～2007.For the first time we monitored moderate level resistance to buprofezin in Jiangsu province(Jiangpu JPZY) in 2005 and Hainan province(Lingshui HNLS) in 2007 with 28.8 and 19.4 folds,respectively,and other populations collected in Guangxi province (Nanning GXNY and Guilin GLNS),Hunan province(Changde HNCD),Jiangxi province (Xinjian JXXJ),Zhejiang province(Yuyao ZJYY),Anhui province(Hexian AHHX and Qianshan AHQS),Jiangsu province(Nantong JSNT) showed low level resistance to buprofezin from 2005 to 2007 with the resistance ratio ranged from 5.6 to 9.1.While populations of Jiangxi province(Shanggao JXSG),Zhejiang province(Jinhua ZJJH) and Hubei province(Xiaogan HBXG) in 2006 were susceptibility to susceptibility decreasing to buprofezin with resistance ratio ranged from 2.5 to 4.1.During the more than ten～year using period,BPH has developed moderate level resistance to buprofezin.The susceptibilities to imidacloprid were determined by rice stem dipping method in 15 BPH populations of six provinces(region) in 2005.The result showed that:We firstly momitored that the resistance of BPH collected from Nanning GXNN,Guilin GXGL, Changde HNCD and Nanjing JSNJ in August,2005 had reached high to extremely high level,with resistance ratio ranged from 70.3 to 291.9;Subsequently,the resistance of BPH collected from 12 areas of Anhui Province(Ahui AHUI,Hexian AHHX),Zhejiang province (Shaoxing ZJSX,Jiaxing ZJJX,Yuyao ZJYY,Haiyan ZJHY and Tongxiang ZJTX),Jiangxi province(Nanchang JXNC and Xinjian JXXJ) during September to October,2005 had all come to extremely high level,with resistance ratio ranged from 243.4 to 723.1 folds.The imidacloprid～resistant strain of BPH,which was selected for 22 generations with imidacloprid by rice stem dipping method during the 23-generation rearing process with the LC50 increased from 18.75 mg a.i./L to 109.49a.i.mg/L and the resistance ratio increased from 208.4 to 1215.3 folds,gives the realized heritability(h2) 0.0997 during the selective period and shows the development of resistance was fast after having developed high resistance to imidacloprid.The mode of inheritance of resistance to imidacloprid in BPH was studied by susceptible strains(S) and resistance(R,RR=1600.6),the reciprocal cross F1(♀R×♂S),F'1 (♀S×♂R),selfing cross(F2),back cross(BC) and from their dosage-mortality curves constructed from the response of 3rd instar nymphs of to imidacloprid treatment.It was found that the mode of inheritance of resistance to imidacloprid in BPH was autosomal and incompletely dominent,with a degree of dominance 0.6325(F1) and 0.5840(F'1),and the resistance showed polyfactoral inheritance.The results of cross resistance research indicated that imidacloprid resistant population showed no cross resistance to fipronil and thiamethoxam.Therefore,fipronil and thiamethoxam could be used alternatively with imidacloprid in the field where imidacloprid has been often used to control this pest. |
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