RESISTANCE OF BROWN PLANTHOPPER (BPH) Nilaparvata Lugens (St(?)l) (Homoptera: Delphacidae) TO BUPROFEZIN AND IMIDACLOPRID

The brown planthopper (BPH) Nilaparvata Iugens (StAl) has long been one of the most devastating pests to rice crop in Asia. Chemical control is.the main method to diminish the damage of BPH by now. Buprofezin and iniidacloprid are the major insecticide for BPH's control at present. Used for long time and in large area, the resistance of BPH to these two insecticides has been focused on for a long time. In order to clear the resistance level and assess the resistance risk to these two insecticides and evaluate the genetics and the management of resistance to buprofezin in BPH ,we conducted this experiment. Here are some results of the studies. 1. A standard bioassay method梤ice-stem dipping method and the susceptible base-line of the BPH's third instar nymphs to these two insecticides was established to monitor the resistance to buprofezin and imidacloprid in BPH. The base-line for BPHthird instar to buprofezin is Y=6.6499+2.8865x, LC50.268 mg a.i.IL; to imidacloprid, Y7. 1422+2.0792x, LC 50=0.09 mg a.i./L. This method had been used to monitor the variation of susceptibility to buprofezin and unidacloprid in BPH populations collected in Nanning and Guilin cities in Guangxi Zhuang Autonomous Region, Aning city in Anhui province, Jiangpu county ,Yizheng and Nantong cities in Jiangsu province from 1996 to 1999; The results shows that all these populations were susceptible or declined susceptible to buprofezin from 1996 to 1999 with the RR ranged from 1.4 to 3.5. All the populations collected during 1996 and 1999 were susceptible or showed low level resistance to imidacloprid, the RR ranged from 1.4 to 6.3. developed low level resistance to imidacloprid with a RR.of 6.3. 2. Results of selection experiments indicates that when selected with interval,the BPH would develop resistance to buprofezin and imidacloprid quite slowly. During the 36-generation rearing process (Fg- F36) in laboratory, the BPH had been selected with buprofezin for 27 generations with the LC50 increased 507.6 folds,gives a (realized heritability) of 0.264. Of the selection process, the former part (F025) been selected 16 generations with several interval (F6-F9, 15 --- F17, F19F20),with the LC increased 0.44 fold, gives a h2 of 0.028 to buprofezin in BPH; the latter part (F2g) , which been selected continuously for 15 generations, with the LC50 increased 737.7 fold , gives a h2 of 0.406. While in process of imidacloprid selection experiment,.during the 32-generation rearing period,the PBH had been selected for 23 generations with several intervals. Results indicates that BPH developed resistance to imidacloprid very slowly in such case. 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. When the imigration was not taken into consideration, the resistance developed quite slowly during the 25 generations of discontinicous selection phase, while rapid increased during the successive selection.. The time for the BPH, which had been discontinicously selected, to 10- fold its LC50 at the selective pressure of 90% and 99% was 61 and 40 generations respectively. While in the successive-selection,the BPH increased its LC50 at the same pressure just after 2 generations. It was verified that the development of resistance in selection with interval ,which similar to the situation of the buprofezin's usage in rice field is significantly delayed comp...