Objectives of Biological Control: Prevention

The objective of prevention biological control is to keep the population of a potential pest from reaching a high, or economic, level. Rather than waiting until a threshold has been exceeded by the potential pest (exceeding the threshold makes it a "pest" by definition), as with reduction, prevention requires early intervention, before a pest buildup occurs. A graphical illustration of prevention is shown below. Population level is shown on the y-axis, and time on the x-axis. In yellow is the threshold that, when exceeded, makes the species a pest. The blue lines represent increases of three hypothetical populations. The one that exceeds the threshold is in the absence of early intervention, to "prevent" the increase. The other two lines show population increases, but neither reaches pest status, due to increased impact of the natural enemy when the "pest" is at low levels. The action of a natural enemy early in the life cycle of the potential pest can keep the population from reaching pest status. What is important to realize from the illustration, is that the population still may increase, but not exceed the threshold -- thus, pest status has been prevented.

Prevention is not appropriate or possible to use against every pest, nor are all natural enemies appropriate to be used in this manner. This objective requires a great deal of information about the pest and the crop (or other) system, and the ability to intervene early. For example, if the pest is predictable, year in and year out, at a certain time if conditions are appropriate, then one could anticipate a buildup of the pest population and intervene early, before the buildup exceeded a threshold. Likewise, a natural enemy that can incur mortality when the potential pest is at a low density will be required.