Abstract: Bioassay showed that the rice stem borer, Chilo suppressalis (Walker), collected from Cixi City, Zhejiang Province, possessed 37.7 and 52.7-fold resistance against monosultap and methamidophos respectively compared with a susceptible population collected from Taihu County, Anhui Province. The activities of microsomal O-demethylase and N-demethylase in the resistant population were 3.3 and 1.34fold higher than those in the susceptible population. There was, however, little difference in the activities of esterase and glutathione S-transferase between the resistant and susceptible population. These findings suggest that the increased activities of microsomal O-demethylase and N-demethylase may be important mechanisms involved in the resistance of the rice stem borer to methamidophos and monosultap. In order to find the hypothesized monosultap-resistant related point mutation, cDNA fragments encoding Chilo suppressalis nAChR α1 (Csα1)subunit were amplified using the RT-PCR technique from susceptible and resistant individuals. Though no unique mutation was found in resistant individuals, the pattern of single nucleotide polymorphisms was described and discussed. There were a total of 33 single nucleotides polymorphisms, of which 14 resulted in amino acid polymorphisms. An insertion was also found in two of the nine cDNAs.

Key words: Chilo suppressalis, insecticide resistance, biochemical mechanism, nicotinic acetylcholine receptor(nAChR), α subunit, single nucleotide polymorphism (SNP)