Insecticide resistance in field populations of Laodelphax striatellus Fallen (Homoptera: Delphacidae) in China and its possible mechanisms

Small brown planthoppers, Laodelphax striatellus Fallen, were collected from six provinces in China, and their resistance to common insecticides surveyed. The strains collected from Jiangsu province were found to be the most resistant, and showed high resistance to imidacloprid and moderate resistance to chlorpyrifos, acephate and deltamethrin ( resistance factors, RF ranged 66- 108, 31-50, 17 - 24 and 12 - 21, respectively). Another two strains collected from Fujian and Guangdong provinces also displayed moderate or low level resistance to imidacloprid, chlorpyrifos and acephate ( RF ranged 27 - 29, 10 - 12, and 9 - 13, respectively). However, the strains collected from Shandong and Yunnan provinces showed little resistance to any of the insecticides tested ( RF < 6). The sensitivity of the strain collected from Hebei province ( the most sensitive one) was similar to that of the susceptible strains previously reported. In all the strains tested, no obvious resistance to fipronil and carbosulfan was found, although the sensitivity of Jiangsu strains decreased by 5-8-fold. Biochemical analysis proved that the enhanced activity of cytochrome P450 monooxygenase (MFO) and esterase, as well as the AChE insensitivity, could all contribute to multiple resistance in this pest.