Resistance Level of Myzus persicae to Methomyl and λ-Cyhalothrin in Guizhou Tobacco Fields

In order to provide a basis for the reasonable application of insecticides and controlling M.persicae in Guizhou province,the resistance level of 34 M.persicae field populations to methomyl and λ-cyhalothrin collected from nine districts was determined with dipping method.The results showed that compared with the susceptible strain,the average resistance ratio of aphids collected from nine districts to methomyl ranged from 2.53 to 5.13,and that to λ-cyhalothrin ranged from 3.15 to 4.44.For methomyl,the average resistance of aphids collected from Liupanshui developed to low level,and the average sensitivity of aphids collected from Bijie,Qiannan,Anshun,Tongren,Qiandongnan and Zunyi was at the decreasing level.For λ-cyhalothrin,the average sensitivity of aphids in all nine districts was at the decreasing level.In all the 34 populations tested,the resistance to methomyl of aphids collected from Shuicheng,Bijie,Jinsha,Changshun,Guiding,Ziyun and Dejiang developed to low level and the resistance ratio ranged from 5.20 to 8.56.The resistance to λ-cyhalothrin of aphids collected from Ziyun,Panxian,Xingyi and Zhenyuan developed to low level and the resistance ratio ranged from 5.39 to 5.82.The other strains were still sensitive or at the sensitivity-decreasing level to the tested insecticides.