Biological control is the use of natural enemies such as predators, parasites, and pathogenic micro-organisms or antagonists to control pests or diseases. This can be achieved either through conservation and stimulation of indigenous natural enemies or by the importation and mass introduction of exotic natural enemies.
Introducing foreign natural enemies (classical biological control) is a complex matter that is not within reach of individual farmers. It involves years of studies by specialists in this field, government regulations, quarantine, etc.
But conservation and stimulation of the defenders that are present in the field is very much the responsibility of the farmer. To conserve defenders, farmers should avoid or even abandon the use of poisonous chemicals (pesticides) as these products kill the defenders.
But farmers can also manipulate the environment to create optimum conditions for spiders and beneficial insects. Flowering plants can provide a source of food (nectar) and shelter for parasitic wasps. Decomposing organic material will contain small insects that provide food for spiders and other predators.
Farmers can even increase the numbers of defenders by “rearing” them. Instead of destroying collected egg masses of pest insects, the farmer can keep them in such a way that emerging egg parasites can survive and return to the field (see: Emergence boxes). Some predators (e.g. earwigs) can easily be mass produced on the farm.
Some beneficial insects that are more difficult to rear can be mass produced in laboratories (e.g. Trichogramma wasps). Farmers can then buy them and release them in the field.
Antagonistic fungi such as Trichoderma can also be mass produced and are commercially available to be used as biological control agents. They can be of help in the management of several soil borne diseases.