一种农药在同一种病虫上反复使用,经过一定时间后,药效明显减退,甚至不再有效。这种现象就是病虫在长时间反复接触这种药剂以后所产生的抗药性。目前,已经产生抗药性的害虫种类已达600余种,其中绝大部分是农业害虫。病菌发生抗药性的种类也有数十种之 A pesticide repeatedly used on the same pest and disease, after a certain period of time, the efficacy was significantly reduced, or even no longer valid. This phenomenon is the resistance of pests and insects to repeated exposure to such agents over a long period of time. At present, there are more than 600 species of insect pests that have developed resistance, the vast majority of which are agricultural pests. There are dozens of species that cause resistance to bacteria