Monitoring Of Insecticide Resistance And Resistance Risk Assessment For Fipronil In The Rice Stem Borer, Chilo Suppressalis (Walker)

The rice stem borer,Chilo suppressalis(Walker),is one of major insect pests of rice in China,especially in the valley of Changjiang River.In recent 10 years,population of this pest and its damage to rice increased dramatically,severely threatening the high and stable yields of rice.For a long time,populations of C.suppressalis are controlled mainly by the use of chemical insecticides.Insecticide resistance in C.suppressalis was one of the main factors for its infestation increase.The aims of present study include:to investigate current situation of resistance in C. suppressalis to ten insecticides in Zhejiang,Jiangsu and Anhui provinces in 2006-2007;to evaluate the susceptibility to six kinds insecticides in five fields populations of C. suppressalis,collected from Zhejiang and Jiangsu provinces in 2007;to estimate realized heritability of resistance against fipronil and JS118 through selection so as to predict resistance development rate.During 2006-2007,insecticide resistance was determined with populations from three provinces Zhejiang,Jiangsu and Anhui.Results showed:(1) Fipronil is a more recently introduced insecticide for controlling of C.suppressalis, and other rice pest insects in most places.But in Wenzhou and Taizhou area, southeast of Zhejiang province,it had been applied extensively to control heavy in festation of C.suppressalis,since around 1997,two or three years earlier than other places and with more application times each year.Moderate resistance levels to fipronil were monitored in Rui'an and Cangnan populations,while Jiangsu Lianyungang,Donghai and Gaochun populations tested were susceptible or decreased susceptibility.(2) A low level of resistance to Abamectin was detected in Cangnan population for the first time in our laboratory(RR=7.6 fold),and other populations tested still remained susceptible to Abamectin. (3) The resistance to triazophos was varied greatly,from having extremely high levels of resistance in Rui'an,Cangnan and Gaochun populations,to being susceptible in Lianyungang population.Donghai and Huangshan populations showed decreased susceptibility.(4) Monosultap.Almost all populations monitored were resistant to it in varying degree.Extremely high levels of resistance to monosultap occurred in Cangnan, Rui'an and Gaochun populations.Moderate level in populations from northern of Jiangsu province(Liangyungang and Donghai populations).(5) During 2006-2007,Cangnan populations had high levels of resistance to chlorpyrifos(61.9 and 91.7-fold respectly),Rui'an populations had moderate or high levels of resistance to it(39.3 and 40.5-fold respectly).Gaochun populations had low level resistance to chlorpyrifos(RR=8.8-fold)in 2006 and moderate level resistance to it(RR=22.6-fold)in 2007.Lianyungang and Donghai populations had no obvious resistance to this insecticide(2.4～5.4-fold).(6) Rui'an and Cangnan populations had moderate or high levels of resistance to cyhalothrin,fenvalerate,beta-cypermethrin,beta-cyfluthrin and deltamethrin, while Lianyungang,Donghai and Gaochun populations had low or moderate levels of resisitance to cyhalothrin,fenvalerate,beta-cypermethrin and deltamethrin (5.3～31.2- fold).Gaochun and Lianyungang populations tested were susceptible to fenvalerate,Donghai Population from Jiangsu province showed decreased susceptibility to it.The susceptibility to several kinds of insecticides was evaluated in five populations of the rice stem borer,Chilo suppressalis(Walker),The resistance management strategies were proposed according to the local situation.In our laboratory,the RA05 population been selected uncontinuously with fipronil for 10 generations,this colony had completed 21 generations in laboratory.Selected stra.i.n was 32.39 fold resistant to fipronil,0.60 times higher than that pre-selection.Realized heritability(h~2) estimated from selection was 0.2069.In our laboratory,the LYG05 population been selected uncontinuously with JS118 for 8 generations,this colony had completed 14 generations in laboratory.Selected stra.i.n was 2.00 fold resistant to JS118,-0.22 times higher than that pre-selection.Realized heritability (h~2) estimated from selection was -0.0956 and showed that the development of resistance to JS118 is very slow.