| The brown planthopper (hereinafter called BPH) , Nilaparvata lugens (Stal) is one of the most serious pests of rice in Asia. Nowadays, Buprofezin and imidacloprid are the two major insecticides for its controlling. In order to control this pest effectively in field, it is necessary for us to study the resistance of these two insecticides to BPH.In our laboratory, BPH been selected continuously with imidacloprid for 15 generations with the LC50 increased 7.56 folds and the RR got 13.9 folds compared with susceptible strain (JPS93), gives a h2 (realized heritability) of 0.0523 and shows that the development of resistance to imidacloprid is slow. Of the selection process, the former part (F0~F10) being selected 10 generations with the LC50 increased 0.24 fold, gives a h2 of0.0257 to imidacloprid; the latter part (F10~F15) being selected 5 generations with the increased 0.54 folds, gives a h2 of 0.1188. Based on h2, the conclusion is that the development of resistance in the former part is significantly slower than in the latter part. Forecast of resistance development was made according to the results of selection experiments. It shows that the generations for a 10-fold increasing of LC50 is negatively related to the h2 and selective pressure. At the selective pressure of 90%, when h2 is 0.0257 and 0.1188, the time for BPH increasing 10-fold its LC50 is 55 and 13 generations, respectively.The buprofezin-resistant strain of BPH (ABF52), which was selected for 43 generations with buprofezin during the 52-generation rearing process with the LC50 value of 311.3mg a.i./L and the RR of 1369.6 folds, was selected continuously for 15 generations (AQR1-AQR15) again with the LC50 value of 1099.3 mg a.i. /L and the RR of 4101.7 folds. In the former part (AQR1-AQR12), the strain was selected for 12 generations, the resistance ratio only rose from 1406.3 folds (AQR1) to 1412.7 folds (AQR12), therefore, the development of resistance in this process was extremely slow. While the LC50 of AQR13 increased to 964.5 ( 778.6 ~ 1270.8 ) mg a.i./L, which was significantly different fromthat of AQR12(378.6(301.1 ~ 503.7) mg a.i./L), indicating that the resistance of buprofezin-resistant BPH has potential of development after continuous screening.A FI genetic detection method of iso-female lines (F1 screen) was used to detect frequency of early resistance alleles to buprofezin in BPH population. 225 isofemale lines, collected from Jiangpu county, Jiangsu province in 2003 was detected by the method. The results showed that the frequency of resistance alleles to buprofezin and its 95%FL were 6.49% (1.50-11.48%). Therefore, F1 method can substitutes for F2 method to detect early frequency of resistance alleles.Metabolic mechanisms of resistance in BPH to buprofezin has been investigated by enzyme synergists (SV1, PBO and DEM) .The synergism ratio of SV1, PBO and DEM to buprofezin was 1.9,1.6, and 1.4 fold in susceptible strain, respectively; 3.0,2.4 and 2.1 fold in resistant strain, respectively. Ratios between resistant strain and susceptible strain were 1.6, 1.5and 1.5 fold, respectively. The result indicated that the enzyme synergists show no significant synergism to buprofezin. Therefore, it can be concluded that the enhanced activity of esterase, mixed-function oxidase and glutathione S-transferase is not the resistant mechanisms of buprofezin in BPH.The toxicity of buprofezin , acetamiprid , fipronil and imidacloprid to imidacloprid-resistant BHP and unselected BPH was studied. When assayed by rice stem-dipping method and topical application, the LC50 of imidacloprid-resistant BPH population (NNR12) to acetamiprid is 1.7 and 2.4 folds, respectively, compared with that of the unselected BPH population (NNY44). The results indicated that imidacloprid-resistant population showed intermediate level of cross resistance to acetamiprid , while no cross resistance to buprofezin and fipronil. Therefore, buprofezin , fipronil and imidacloprid can be used alternatively for the control of this pest.The influence of lambda... |
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