Resisrant Selection Of Brown Planthopper To Imidacloprid And Detection Of The DNA Polymorphism

Brown Planthopper is one of main rice insect pests. Currently, imidacloprid is an important pesticide. However, it is found that brown planthoppers have developed high level resisrance to imidacloprid recently. In order to investigate the rules of the resistance of brown planthopper to imidacloprid, the resistant selection and toxicity test were studied in laboratory generation by generation.The DNA variation and methylation mutation were detection in this study. The following results were obtained:1. Start with sensitive strains,23generations were selected continuously, in which the former18th are selected with imidacloprid, whereas the latter5th generations are without pesticide. The result showed that the values of LC50and the resistant levels increased gradually generation by generation, of which the F18generation was the highest, values are101.49mg/L and180.3times, respectively. Our results show that it is necessary to control the concentration and frequency of imidacloprid, which would be useful for lengthen their service life.2. By using20ISSR primers,49loci were identified, of which only one site display polymorphism within samples. With25pairs of AFLP primers,111loci were obtained, of which11site display polymorphisms within samples. The highest and lowest ratios of polymorphisms are10.2%and1.69%, occurred at the eighth and first generation, respectively. The polymorphism change trend indicates that, in the early screening stage (the earliest three generations), the brown planthopper responses genetically to imidacloprid quickly; in the middle screening stage (from4th to6th generations), its responses fluctuated substantially with a AFLP values of1.69%-8.47%; in the late screening stage (from7th to9th generations), its responses varies very little reaching a AFLP values of6.78%-10.2%. These results shows that imidacloprid can induce DNA mutation in brown planthopper, therefore onset of resistance to insecticides. Our results provide important information on moleular mechanism of brown planthopper resistance to imidacloprid.3. In order to know whether DNA methylation take part in defense functions of brown planthopper genome at resistance to insecticides,9generations were sprayed by imidacloprid continuously. AFLP technique was used to test the DNA methylation polymorphism variation of brown planthopper during the continuous application of imidacloprid. With25pairs of AFLP primers,120loci were obtained, of which15loci, including78bands, display polymorphisms within samples. The highest and lowest ratios of polymorphisms bands are10.2%and1.28%, occurred at the fifth and sixth generation, respectively. The polymorphism change trend indicates that, in the early screening stage (the earliest three generations), the brown planthopper responses genetically to imidacloprid quickly with a AFLP values of3.85%-6.41%; in the middle screening stage (from4th to6th generations), its responses fluctuated substantially with a AFLP values of1.28%-10.26%; in the late screening stage (from7th to9th generations), its responses varies very little reaching a AFLP values of5.13%-7.69%. These results shows that imidacloprid can induce DNA methylation mutation in brown planthopper, therefore onset of resistance to insecticides. The results of this study showed that DNA methylation take part in planthopper’s DNA genome defense imidacloprid selection.