Natural biological control
Levels of both major and minor crop pest infestations vary between fields and years but are frequently regulated by their natural enemies (beneficial insects). Pesticides are only needed when the pests escape this control.
To encourage robust control at all times and locations, it is essential that a wide range of natural enemies are present, capable of controlling each of the pest's life stages. Different species may also work together (act synergistically), for example, parasitic wasps may cause aphids to fall to the ground, where they are subsequently predated by ground-foraging natural enemies.
To maximise pest control, it is important to encourage not only the species playing a major contribution, such as hoverflies (page 190) and parasitic wasps (page 194), but also overall levels of natural enemies providing background levels of control that prevent pests reaching outbreak levels.