Abstract: Relative toxicity index of 11 insecticides belonging to six different categories against the 3rd-instar nymphs of Laodelphax striatellus (Fallén) and the resistance of the nymphs from 7 typically ecological sites in East China to 10 of these insecticides were surveyed with rice seedlings-dipped method. The results indicated that the toxicity of acephate was the lowest among the 11 insecticides, which was used as reference standard herein. The relative toxicity of the other 10 insecticides to the nymphs in a descending turn was fipronil, buprofezin, abamectin, thiamethoxam, alpha-cypermethrin, IPP (a new nitromethylene-compound), chlorpyrifos, dichlorvos, triazophos and imidacloprid. Compared with Yunnan (YN) susceptible population collected from fields of Chuxiong, Yunnan province in 2001, the 7 field populations respectively from Jurong (JR), Tongzhou (TZ), Chuzhou (CZ), Dafeng (DF), Nanjing (NJ) and Suzhou (SZ) of Jiangsu province and Lujiang (LJ) of Anhui province in 2007 showed very high resistance to buprofezin with the resistance ratio over 200-fold, and medium or high resistance to alpha-cypermethrin with the resistance ratio of 7.8-108.8 fold. The LJ population showed 7.7- and 12.0-fold resistance to triazophos and chlorpyrifos, respectively, and the CZ, NJ, DF and JR populations showed 5.7-12.6-fold resistance to chlorpyrifos. All the 7 field populations of L. striatellus were sensitive to dichlorvos, fipronil, avermectins, imidacloprid, thiamethoxam and IPP.

Key words: Laodelphax striatellus, insecticide resistance, insecticides, relative toxicity, resistance ratio