由于天然的生物控制,许多昆虫种群长期被控制在低的密度水平,相对来说,这对于未受干扰的系统(如森林)更为明显。但是,即使在人为高度影响的农业生态系统中也有这种情况。这些昆虫因一般不超过经济危害水平,所以人们并不认为它们是害虫。 Due to natural biological control, many insect populations have long been controlled at low densities, which is relatively more pronounced for undisturbed systems such as forests. However, this is true even in highly man-made agro-ecosystems. Because these insects generally do not exceed the level of economic harm, so people do not consider them pests.