Studies On The Susceptibility Of Several Kinds Of Insecticides And Resistance Risk Assessment For Fipronil In The Small Brown Planthopper, Laodelphax Striatellus Fallén (Homoptera: Delphacidae)

The small brown planthopper, Laodelphax striatellus Fallen is one of the most important insect pests of rice. It can transmit some virus diseases, for example, the rice stripe virus, rice black streak dwarf virus and maize rouge dwarf virus. In recent years, population of this pest and its damage to rice increased dramatically in Jiangsu Province and Zhejiang Province, severely threatening the high and stable yields of rice.The susceptibility to 29 insecticides was evaluated in five field populations of the small brown planthopper, collected from Wuxi city, Yancheng city, Jiangsu Province and Huzhou city, Zhejiang Province in 2005 and 2006. The results detected by rice stem dipping method showed that the toxicity of fipronil and silafluofen was highest for the WX05 population, the toxicity of thiamethoxam was relatively high; the toxicity of fipronil and thiamethoxam was highest for the HZ05 population, the toxicity of imidacloprid, etofenprox and silafluofen was relatively high; the toxicity of fipronil was highest for the YC05 population, the toxicity of thiamethoxam, imidacloprid and silafluofen was relatively high; the toxicity of carbosulfan, buprofezin, dichlorvos, acetamiprid, promecarb, fenobucarb, isoprocarb, imidaclothiz, propoxur, metolcarb, dimethacarb, dimethoate, malathion, fenoxycarb and cycloprothrin was low for the three populations talked above, in adition to the toxicity of etofenprox and imidacloprid was low to the WX05 population and the one of etofenprox was low to the YC05 population. The toxicity of fipronil and butylene-fipronil was highest for the WX06 population and the HZ06 population, the toxicity of thiamethoxam, nitenpyram, silafluofen, chlorpyrifos, pymetrozine and imidacloprid was relatively high, the toxicity of promecarb, buprofezin, acetamiprid, isoprocarb, lambda-cyhalothrin, dichlorvos, methamidophos, beta-cypermethrin and acephate was low. The recommended insecticides of field efficacy trial or resistance management were fipronil, butylene-fipronil, thiamethoxam, nitenpyram, chlorpyrifos, pymetrozine, silafluofen, isoprocarb and dichlorvos. The toxicity of insecticides on third instar nymphs of different populations was evaluated in our laboratory, the results showed that the toxicity of fipronil, thiamethoxam and imidacloprid for the YC05 population was higher than the WX05 population; the toxicity of silafluofen and dichlorvos was lower than the WX05 population, the toxicity of etofenpros, carbosulfan, promecarb, acetamiprid, fenobucarb, buprofezin and isoprocarb was close to the WX05 population. The toxicity of fipronil, thiamethoxam, etofenprox, imidacloprid, carbosulfan and isoprocarb for the HZ05 population was higher than the WX05 population and YC05 population, the toxicity of silafluofen was higher than the WX05 population and was close to the YC05 population, the toxicity of dichlorvos, acetamiprid, fenobucarb and buprofezin was close to the WX05 and YC05 populations.The susceptibility of insecticides to the populations collected from Wuxi city and Huzhou city in 2005 and 2006. The results showed that the susceptibility of fipronil, imidacloprid, thiamethoxam and isoprocarb for the WX06 population increased significantly compared with the WX05 population, the susceptibility of promecarb, dichlorvos, silafluofen and etofenprox decreased significantly, the susceptibility of carbosulfan, fenobucarb, acetamiprid and buprofezin changed insignificantly; the susceptibility of imidacloprid, thiamethoxam, carbosulfan and fenobucarb for the HZ06 population decreased significantly compared with the HZ05 population, the susceptibility of fipronil, silafluofen, etofenprox, acetamiprid, isoprocarb, promecarb and buprofezin changed insignificantly.In our laboratory, the RF05 population been selected uncontinuously with fipronil for 23 generations with the LC50 increased 1.38 folds and the RR got 18.8 folds compared with the susceptible strain, gives a h~2 of 0.0539 and shows that the development of resistance to fipronil is slow. 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 h~2 and selective pressure. At the selective pressure of 90%, when h~2 is 0.0539 and 0.0886, the time for the small brown planthopper increasing 10-fold is 36 and 23 generations, respectively.The toxicity of buprofezin on first and third nymphs of the WX06 population, and pymetrozine on nymphs of the HZ06 population by rice stem dipping method, the results showed that the toxicity of buprofezin for the first and third instar nymphs was low, and the low toxicity has nothing with instars of insects tested; the toxicity of pymetrozine increased significantly with the prolonging of action time, and the toxicity was recorded 120h and 144h after treatment was close.The resistance to 9 insecticides was evaluated in two field populations of the small brown planthopper, collected from Wuxi city, Jiangsu Province and Huzhou city, Zhejiang Province in April 2006. The results detected by topical application showed that WX05 and HZ05 populations developed high level resistance to imidacloprid, 79.6 folds and 44.6 folds, high level resistance to propoxur, 76.6 folds and 40.1 folds, mid-high level resistance to carbaryl, 29.8 folds and 45.3 folds, respectively, and remained susceptible or low level resistance to diazinon, fenitrothion, fenobucarb, carbosulfan, etofenprox and fenvalerate, 1.4 to 8.1 folds.