Insecticide susceptibility of the small brown planthopper, Laodelphax striatellus Fallen (Homoptera: Delphacidae), collected from East Asia

The insecticide susceptibility of the small brown planthopper, Laodelphax striatellus Fallen, collected from East Asiain 1992-1994, was examined by the topical application method. The LD sub50 values of organophosphorus insecticide for the northern Vietnam populations (HAI, HAN, VIN) and the JIN population (Yunnan Province, China) were smaller than those of the FU (Zhejiang Province, China), IB (central Japan) and KU (southwestern Japan) populations. The LD sub50 values of organophosphorus and carbamate insecticides for the northern Vietnam populations were almost the same as that for the Fukuoka (western Japan) population examined in 1967. The LD sub50 values of organophosphorus insecticides did not differ among the FU (Zhejiang Province, China), IB (central Japan), and KU (southwestern Japan) populations. The LD sub50 values of carbamates for the KU population were the largest, and those for the northern Vietnam population were the smallest. The carbamate susceptibility of acetylcholinesterase in the KU population was lower than that in the HAI population. Therefore, we considered that insensitivity of acetylcholinesterase for carbamate was one of the carbamate resistant factors in the KU population. The LD sub50 values of etofenprox, fenvalerate, and imidacloprid showed no differences among all the populations tested, respectively.