河北省里县辛兴大队是一个集中产棉大队,每年防治蚜虫都使用大量农药,开支甚大,效果不佳。为了有效地控制棉蚜的为害,他们学习外地经验,大面积释放瓢虫。在去年释放成功的基础上,今年释放2400亩(占棉花种植面积的80%),取得了蚜虫虫口减退率达89～98%的良好效果。他们在试验中发现,当麦田蚜株率分别达11.2%、80%、100%时,亩瓢虫数相应达20.8头、270.4头、4160头。在棉田,当蚜株率为20%和40%时,亩瓢虫数达5.6头和56头;当蚜 Xinxing Brigade in Lixian County, Hebei Province, is a concentrated cotton production brigade that uses large amounts of pesticides to control aphids each year, with a large expenditure and poor results. In order to effectively control the damage of cotton aphid, they learn field experience and release ladybug over a large area. On the basis of the success of the release last year, 2,400 mu (80% of cotton acreage) were released this year, and a good effect of aphid population reduction of 89-98% has been achieved. They found in experiments that when the rates of aphids in wheat field reached 11.2%, 80% and 100% respectively, the number of lady beetles corresponded to 20.8, 270.4 and 4160 respectively. In the cotton field, when the rate of aphids is 20% and 40%, the number of lady beetles reaches 5.6 and 56 respectively. When the aphids