Objectives of Biological Control: Delay

The objective of delaying a pest buildup is not intuitive. This objective is similar to prevention, in that both require early intervention, before a population exceeds a threshold. However, delay means that the population will eventually build up to a high level, but it does so at a time when the species is no longer considered a pest. An illustration of this objective is below. The vertical lines represent a time "window," during which a large population of the potential pest will cause damage. If the population is large at other times, outside the window, economic damage does not occur and this species would not be considered a pest.

As an example, the facultatively predaceous mirid, Campylomma verbasci, feeds on apples. If the mirid feeds on apples that are smaller than one inch in diameter, the damage is severe enough that the fruit does not recover -- thus C. verbasci is an economic pest. However, if the apple is larger than one inch in diameter when C. verbasci feeds on it, the fruit can recover from the feeding, thus the mirid would not be considered a pest. Therefore, biological control intervention that can delay the buildup of the mirid population until apples are larger than an inch in diameter would avert economic damage. See Thistlewood and Smith (1996) for details on this study with C. verbasci.