The small brown rice planthopper is an injurious insect on food crop of Ningxia.

灰飞虱是宁夏粮食作物上的一大害虫。

Clanis bilineata tsingtauica is a kind of argricultral injurious insect, distributing in the west and north of china.

豆天蛾是一种大型的农业害虫，在我国西部和北部地区广泛分布。

The prerequisite for the natural enemies to be able to control insect pest is that the increase of injurious insects is restrained by the density of the latter.

捕食天敌能防治病害的前提是害虫猎物数量增长受害虫自身密度的制约。