| Laboratory measurement of resistance of two Tetranychus urticae populations to ten kinds of acaricides was carried out. The susceptibility difference of eggs and adults to ten acaricides was tested. The joint-toxicity of several acaricides and the synergism of five synergists were studied. The resietance selection of Tetranychus urticae to abamectin, fenpropathrin and pyridaben were carried out. The resistance mechanism was evaluated. Besides , the measuring method to eggs and larves was improved.The results could be summarized as follows:1. The resistance of T.urticae Ri population(sampled from Shouguang City, Shandong Province) was 17. 7-fold, 10. 4-fold, 6. 67-fold and 6.63-fold to isocarbophos , fenpropathrin, pyridaben and cyhalothrin ,respectively. The resistance of T. urticae R2 population(sampled from Yantai City, Shandong Proprince) was 10. 9-fold, 31. 3-fold, 9. 36-fold and 15. 5-fold to the four kinds of acaricides.2. Moderate resistance had been occurred in the eggs of T. urticae R: population(sampled from Yantai City, Shandong Province). The resistance ratios were 2.99-fold and 2.08-fold to fenpropathrin and cyhalothrin, respectively.3. The susceptibility of eggs and adults to ten kinds of acaricides was different. Eggs were much more susceptible than adults and have different susceptibility to different acaricides. what is more,the degree of difference of resistant population was more striking than that of susceptible population.4. The results of joint-toxicity measurement showed that the combined application of fenpropathrin with pyridaben , amitraz and dicofol were synergisted, co-toxicity coefficience were 377> 342 and 184. While antagoism were expressed by joint-using fenpropathrin with chlorfenapyr, azocyclotin and cyhalothrin. The synergism was evident for the pyridaben combining with fenpropathrin and amitraz, co-toxicity coefficience were 377 and 249.But when pyridaben was jointly used with chlorfenapyr, omethoate , azocyclotin and isocarbophos, they expressed antagoism.5. The controlling effects of acaricides to T. urticae R2 population in laboratory showed that chlorfenapyr and abamectin had the best effect to T. urticae, azocyclotin and pyridaben were secondary, the others had little effect to T. urticae at the recommending doses in the field. So, they were not fit for the measurment of T.urticae.6. The studies of resistance selection showed that the resistance of T. urticae had reached 6. 72-fold to abamectin, 19. 8-fold to fenpropathrin and 12. 1-fold to pyridaben after treated 12 times in the laboratory, which had formed stabled resistant strains.7. The rise of resistance of T. urticae to abamectin is polyfactorial , which mainly caused by the increased activities of microsomal oxidase -. acetylcholinesterase and glutathione S-transferase, in addition, decreased cuticular penetration is also one of factors. T. urticae is highly resistant to pyridaben because of increased activities of carboxy lesterase and microsomal oxidase. The main cause resistance to fenpropathrin is the increased activities of carboxy lesterase and glutathione S-transferase. In addition, the increased activities of acetylcholinesterase is related to the resistance of T. urticae to fenpropathrin.8. The zymogram of esterase isodyna electrophoresis demonstrated that susceptible strain and three resistance strains all have three obvious enzyme bands. The difference of the color on the bands shows that the resistance of T.urticae to abamectin> pyridaben and fenpropathrin is all concerned with the changes of esterase.
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