Environmental manipulation for the encouragement of natural enemies of pests.
The abundance and diversity of predatory insects within a field has been shown to be closely related to the nature of the surrounding vegetation. Crop monocultures can reduce the densities of many indigenous biocontrol agents that are dependent on the presence and diversity of wild plants in the agricultural landscape.
Several attempts to diversify the agro-ecosystem using a variety of management practices have been carried out. In general, the results of these studies have shown that spatial heterogeneity in the agro-ecosystem can lead to increased community stability, and that predatory animals inhabiting newly created habitats have some ability to exert regulatory effects on their prey populations in the adjacent field areas.
Work at Southampton University has created grass-sown linear 'island' habitats in the centres of three cereal fields. Within two years of establishment, high-density populations of polyphagous predators have been encouraged to overwinter in these new habitats. This has provided a nucleus population at the field centres from which dispersal into the crop can take place in the spring, the time when the predators' biocontrol potential is at its highest.