Rsistance Risk, Cross-resistance And Biochemical Resistance Mechanism Of Laodelphgax Striatellus (Fallén) To Buprofezin And Thiamethoxam

The adults and nymphs of Laodelphax striatellus(Fallén) not only damaged crops directly, but also transmited a variety of plant viral disease. And the wheat, corn and rice yields had been seriously affected. Currently, the most effective method to prevent L striatellus. was chemical control, but at the same time it also brought the resistance problem which could not be ignored. Buprofezin, as a widely used pesticide, had produced different levels of resistance in south China, and the control effect decreased significantly. However, Shandong, Hebei and other northern provinces were the main producing areas of wheat and corn, and L. striatellus resistance levels and mechanisms to buprofezin were unclear. Thiamethoxam was launched to prevention and control L. striatellus in recent years because of the better effect. Currently, L. striatellus of thiamethoxam resistance level was relatively low, but the resistance risk to thiamethoxam was exist.In this experiment, we acquired resistance strains of L. striatellus to buprofezin and thiamethoxam through screening, as the experimental materials to study the risk of resistance and stability, and to clear the cross-resistance and the biochemical mechanism of resistance, thus providing a theoretical basis for the development of rational pesticide use practices and prolong life.1 Establish L. striatellus resistant populationsThis study selected collection of species in the field of the recovery strain and long-term feeding as relatively sensitive strain. Using rice seedlings spraying to screening the L. striatellus of Shandong taian area, it acquired 168.49 folds resistant strains after 32 generations screening with buprofezin, and the screening process of L. striatellus resistance level with buprofezin presented "S" growth. And we acquired 27.74 folds resistance strains after 20 generations screening with thiamethoxam, and the screening process of L. resistance level with buprofezin presented after a slow first rapidly.2 Resistance risk assessment of L. striatellus resistant strainsThe results showed that when reality heritability of L. striatellus to buprofezin and thiamethoxam was 0.105 and 0.164, and the killing rate was 80~90%. Thus the planthopper was expected to buprofezin and thiamethoxam resistance increase l0 times only need 5 to 6 generations, both had quickly generate risk of resistance. Therefore, we should improve the accuracy of forecasting, and combine of different mechanisms of drug mix and exchange in order to delay the development of resistance in field populations.3 Stability of L. striatellus resistant strainsThe buprofezin strain resistance stability was analyzed, when we removed from pesticide treatments for 10 generations, the resistance ratio reduced from 168.49 folds to 130.03 folds. Resistance had decreased, but still relatively high, far to restore the level of screening, indicating relatively stable resistance after screening. For thiamethoxam strains, when we removed from pesticide treatments for 10 generations, the resistance ratio reduced from 27.740 folds to 11.000 folds. Resistance reduce coefficient was 0.0402. To thiamethoxam resistance, although it was not recovered the sensitivity level, but the resistance rapidly decreases, therefore, resistance to thiamethoxam was still in an unstable phase.4 Cross-resistance of L. striatellus resistant strainsThe result of experiment was clear that buprofezin strain presenced high levels of cross-resistance with thiamethoxam(42.629 folds) and imidacloprid(34.397 folds), and presenced moderate levels of cross-resistance with acetamiprid(29.032 folds), and there was no cross-resistance with pymetrozine(1.173 folds) and chlorpyrifos(1.052 folds). Thiamethoxam strain only presenced low levels of cross-resistance with imidacloprid(6.437 folds) and acetamiprid(5.381 folds), while buprofezin, pymetrozine and chlorpyrifos resistance ratios were less than 2, so there was no cross-resistance with these pestcides.5 The biochemical mechanism of L. striatellus resistant strainsBy measuring the synergies, we found that the cytochrome P450 monooxygenase inhibitor PBO synergism to buprofezin was strongest, which the synergism ratio was 2.48 folds; and esterase inhibitor TPP synergies to buprofezin was second, which the synergism ratio was 1.79 times; and glutathione-S-transferase inhibitor DEM synergies to buprofezin was not obvious, which the synergism ratio was 1.10 times. The determination of detoxification enzyme activity also showed similar results. Resistant strains of buprofezin cytochrome P450 monooxygenase activity was highest, which was 2.35 folds of the susceptible strain, and esterase activity was also significantly higher, which was 1.68 folds of the susceptible strain, and glutathione-S-transferase among strains showed no significant difference. Similarly, the cytochrome P450 monooxygenase inhibitor PBO synergism to thiamethoxam was strongest, which the synergism ratio was 3.36 folds; and esterase inhibitor TPP synergies to thiamethoxam was second, which the synergism ratio was 2.73 times; and glutathione-S-transferase inhibitor DEM synergies to thiamethoxam was not obvious, which the synergism ratio was 1.45 times. The results of detoxification enzyme activity showed that resistant strains of thiamethoxam cytochrome P450 monooxygenase activity was highest, which was 2.28 folds of the susceptible strain, and esterase activity was also significantly higher, which was 1.18 folds of the susceptible strain, and glutathione-S- transferase among strains showed no significant difference.The results showed that cytochrome P450 monooxygenase in L.striatellus for buprofezin and thiamethoxam resistance played a leading role in the formation, and it may participate in the resistance formation.