Studies On The Susceptibility To Seven Kinds Of Insecticides And Resistance Risk Assessment To Imidacloprid In The White-Backed Planthopper, Sogatella Furcifera (Horvath) (Homoptera: Delphacidae)

The white-backed planthopper,sogatella furcifera(Horvath) is one of the most important pests of rice crop in our country.Since 1980s,the damage caused by white-backed planthopper was more and more serious,and made severe loss on rice production.So it is necessary to study the susceptibility or resistance to several kinds of insecticides of it in order to control this kind of pests effectively in the field.The susceptibility to 21 insecticides which could be fallen into seven categories such as organophophates,carbamates,pyrethiods,neonicotinoids,phenylpyrazole perivatives, IGRs and pyridine azomethines were evaluated by rice stem dipping method against the third instar nymphs of sogatella furcifera in field populations which were collected from Jiangpu district of Nanjing,Jiangsu province in 2006(JP06).The results showed that the toxicity of thiamethoxam was the highest with its LC₅₀ value 0.08 mg a.i./L;the toxicity of buprofezin,imidacloprid,nitenpyram,butylene-fipronil,pymetrozine,acetamiprid, imidaclothiz,chlorpyrifos and fipronil was next to thiamethoxam with their LC₅₀ values 0.25-2.66 mg a.i./L;and the other pesticides had the lower toxicity.Among all the insecticides tested,the number of insecticides whose toxicity were higher than methamidophos was 18,and the number whose toxicity were higher than chlorpyrifos which was being normally used was 9.The susceptibility to the above insecticides was evaluated against sogatella furcifera which were collected from Jiangpu district in 2007(JP07).The results indicated that thiamethoxam,buprofezin and imidacloprid had the highest toxicitiy with their LC₅₀ values 0.04-0.11 mg a.i./L;nitenpyram,butylene-fipronil,pymetrozine,acetamiprid,imidaclothiz, chlorpyrifos,fipronil,silafluofen showed good efficacy with their LC₅₀ values 0.27-4.73 mg a.i./L.Among the insecticides,the number of insecticides whose toxicity were higher than methamidophos was 15,and the number whose toxicity were higher than chlorpyrifos was 9.The recommend insecticides for field efficacy trial or resistance management were thiamethoxam,buprofezin,imidacloprid,nitenpyram,butylene-fipronil,pymetrozine, acetamiprid,imidaclothiz,chlorpyrifos,fipronil,isoprocarb and dichlorvos.According to the year-to-year variation in the susceptibility of sogatella furcifera to the tested insecticides between 2006 and 2007,it was noted that the susceptibility of sogatella furcifera to buprofezin,imidacloprid,acetamiprid,fipronil were increased;the susceptibility to chlorpyrifos,dichlorvos,carbosulfan,metolcarb were decreased significantly with decreased folds were 2.2,2.0,2.5,2.5;the susceptibility to other insecticides changed insignificantly.In our laboratory,the imidacloprid-selected strain of sogatella furcifera,which was selected uncontinuously for 18 generations by rice stem dipping method during the 19-generation with the LC₅₀ increased from 1.246 mg a.i./L to 3.519 mg a.i./L,the increased fold of resistance was 1.82,gives a h² of 0.0990.Forecast of resistance development was made according to the results of selection experiments,it shows that the generation for a 10-fold increasing of LC₅₀ is negatively related to the h² and selective pressure.At the selective pressure of 90%,when h² is 0.2295 and 0.0990,the time for the resistance of sogatella furcifera increasing 10-fold is 5 and 10 generations,respectively.The co-toxicity of imidacloprid mixed with chlorpyrifos,imidacloprid mixed with buprofezin and nitenpyram mixed with buprofezin in different ratio was assayed by rice stem dipping method against the third instar nymphs of sogatella furcifera.The results showed that the CTC of imidacloprid mixed with chlorpyrifos in the ratio of 5:1 is 126.1; the CTC of imidacloprid mixed with buprofezin in the ratio of 1:5 and 1:3 are 306.8,167.8 respectively,which showed additive effect;and the CTC of nitenpyram mixed with buprofezin in the ratio of 1:1 and 3:1 are 138.0,127.7 respectively,which also showed additive effect.The toxicity of pymetrozine on the third instar nymphs of JP07 population in different action time and the susceptibility of sogatella furcifera on different generation to chlorpyrifos was evaluated by rice stem dipping method.The results showed that the toxicity of pymetrozine increased significantly with the prolong of action time;and the susceptibility of sogatella furcifera on F₁ and F₂ to chlorpyrifos has no difference.