Abstract: In order to clarify whether DNA methylation takes part in insecticide resistance, the 3rd instar nymphs of the brown planthopper, Nilaparvata lugens, in 9 generations were sprayed by imidacloprid continuously in the laboratory, and AFLP technique was used to test the variation in DNA methylation polymorphism of the brown planthopper during the continuous application of imidacloprid. Using 25 pairs of AFLP primers, we obtained 120 loci, of which 15 loci displayed polymorphism within samples and a total of 78 polymorphic bands were obtained for these loci. The highest and lowest rates of polymorphic bands, 10.26% and 1.28%, occurred at the 5th and 6th generation, respectively. The change trend of polymorphism indicated that in the early screening stage (the earliest three generations), the brown planthopper had quick responses to imidacloprid with the rates of polymorphic bands of 3.85%-6.41%; in the middle screening stage (from the 4th to 6th generation), its responses fluctuated substantially with the rates of polymorphic bands of 1.28%-10.26%; and in the late screening stage (from the 7th to 9th generation), its responses varied very little with the rates of polymorphic bands of 5.13%-7.69%. These results suggest that imidacloprid can induce DNA methylation in the brown planthopper, therefore onset of resistance to insecticides, and DNA methylation may take part in the genome defense of planthoppers to imidacloprid selection.

Key words: Nilaparvata lugens, imidacloprid, insecticide resistance, DNA methylation, polymorphism, AFLP