２００２年７月下旬至８月上旬，沁阳市玉米田三代黏虫暴发成灾，发生面积达４０００hm２以上。玉米有虫株率达１００％，平均单株虫量一般５～６头，最高达１４头，玉米叶片被吃光，并咬食花丝和雄穗。从田间调查情况看，凡是被冰雹砸过的地区，黏虫都发生很重。究其原因：①? From late July to early August 2002, three generations of armyworm outbreaks in the corn field of Qinyang City hit the area of ​​over 4000hm2. Maize has a worm rate of 100%, the average number of individual insects generally 5 to 6, up to 14, corn leaves were eaten, and bite the filaments and tassels. Judging from the field investigation, any area hit by hail has a lot of weight. The reason: ①?