乳源县地处粤北山区。六十年代中期以前,危害水稻生产的主要害虫有三化螟、负泥虫和铁甲虫;稻纵卷叶螟和稻飞虱只是间歇发生。六十年代中期以后,稻纵卷叶螟每年发生面积由过去占水稻面积的1—2成上升到5—7成,稻飞虱发生面积也由1—2成上升到5—6成。这两种害虫的为害程度,多数年份也是严重的。三化螟严重发生的间隔时间也缩短了。 Ruyuan County is located in northern mountainous area. Before the mid-1960s, the main pests that endanger rice production were the three rice borers, the negative mud worms and the iron beetles; the rice leaf roller and the rice planthoppers only intermittently occurred. After the mid-1960s, the annual occurrence of Cnaphalocrocis medinalis increased from 1-2% of the area occupied by rice in the past to 5-7% and the occurrence of planthoppers rose from 1-2% to 5-6%. The extent of the harm of these two pests, most of the year is also serious. Severe occurrence of three borer interval also shortened.