Studies On Risk, Early Detection And Management Of Resistance To Imidacloprid And Buprofezin In Nilaparvata Lugens (St(?)l)

The brown plant-hopper (BPH) Nilaparvata lugens (Stal) has long been one of the most devastating pests to rice crop. Buprofezin and imidacloprid are the major insecticides for controlling BPH at present. It is very important to detect the early resistance in order to take out and implement preventive resistance management strategy and measures.A F1 genetic detection method of iso-female lines (F1 screen) was established to detect frequency of early resistance alleles to buprofezin in BPH population. 168 isofemale lines, collected from Jiangpu county, Jiangsu province in 2001 and 172 isofemale lines from Nanning city, Guangxi province in 2002 were detected by the new method; The results showed that the frequency of resistance alleles to buprofezin and its 95%FL were 4.65%(0.22~9.08%) and 10.28%(3.97~ 16.59%), respectively. At the same time, the populations of two areas were detected by F2 genetic detection method of iso-female lines (F2 screen) and the results were 4.86 % (0 - 9.79%) and 10.0% (3.77 ~16.23%), respectively. Because F1 method is easier than F2 method and the 95% FL of two methods is almost overlap, F1 method can substitutes for F2 method to detect early frequency of resistance alleles. Based on the detection results, preventive resistance management strategy and measures should be worked out and implemented as soon as possible.In our laboratory, BPH been selected continuously with imidacloprid for 17 generations with the LC50 increased 8.91 folds and the RR got 16.1 folds compared with susceptible strain (JPS93), gives a h2 (realized heritability) of 0.1174 and shows that the development of resistance to imidacloprid is slow. Of the selection process, the former part (F0-F12) being selected 12 generations with the LC50 increased 0.68 fold, gives a h2 of 0.0352 to imidacloprid; the latter part (F12~-F17) being selected 5 generations with the LC50 increased 4.88 folds, gives a h2 of 0.3676. 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 0.0352 and 0.3676, the time for BPH increasing 10-fold its LC50 is 35 and 5 generations, respectively.The buprofezin-resistant strain of BPH (ABF36), which was selected for 27 generations with buprofezin during the 36-generation rearing process with the LC5o value of 310.2 a.i. mg/L and the RR of 1364.7 folds, was selected continuously for 20 generations (AQR1~AQR20) again with the LC50 value of 378.8 a.i. mg /L and the RR of 1666.5 folds. During the selection process, the strain (AQR7) was purified by single-pair mating method. The former part (AQR1-AQR6) of purified strain being selected 6 generations, gives a h2 of 0.0127 to buprofezin; the latter part (F43~F56) of purified strain being selected 13 generations, h2 is 0.0157. Based on the forecast of resistance development, at the selective pressure of 90%, when h2 is 0.0127 and 0.0157, the time for BPH increasing 10-fold its LC50 is 73 and 79 generations, respectively. From the above results, a conclusion was made that the development of resistance was quite slow after having developed high resistance to buprofezin.The cross resistance to buprofezin and imidacloprid in BHP was studied. The LC50 of imidacloprid-resistant BPH population (NNR15) to imidacloprid and buprofezin are 6.1 and 0.9 folds, respectively, compared with that of the unselected BPH population (NNF35). The results indicated that imidacloprid-resistant population showed no cross resistance to buprofezin. Therefore buprofezin and imidacloprid can be used alternately for the control of this pest.The relative fitness between susceptible and resistant strains in BPH was studied. The results indicated that the resistant strains possessed reproductive and developmental disadvantage including lowe...