Objectives of Biological Control: Reduction

Reduction of a pest population after it occurs at a damaging level is the easiest situation to consider because it approximates the use of pesticides. A biological control agent is used after the pest population has exceeded the economic threshold, with a goal of sufficiently reducing pest density and maintaining the lower density over a long period of time. It is important to recognize that the pest is not eradicated but simply reduced to non-pest status. A graphical illustration of such a reduction can be seen below. This has been the historical approach for importing natural enemies against exotic pests, such as the introduction of vedalia ladybird beetle to reduce the population level of cottony cushion scale, a serious pest of citrus.