The use of biological methods to control plant diseases and pests is called biological pest control, whereas the beneficial organisms nurtured to deal with pests are known as bio-control agents.
This method relies on natural predation, which is in contrast to the modern-day practice of killing insects and pests with pesticides and insecticides. Organic farming creates a living, vibrant and natural ecosystem in the fields by using natural, green manure, compost, organic insecticides, fertilisers and biological pest-control methods. It requires a detailed knowledge of the different life forms that live in the fields, their life cycles, feeding patterns and preferable habitats, for the bio-control of pests. Bio-control agents include the lady beetles that eliminate aphids and dragonflies that eliminate mosquitoes. All the bio-control agents are conserved under an Integrated Pest Management (IPM) programme.
Bt is a microbial bio-control agent, derived from Bacillus thuringiensis, which is introduced in the fields to control butterflies and caterpillars. When Bt spores are sprayed on plants, the insect larvae consume the spores or crystals of this bacteria, and die. The bio-control agent Bt is also used to develop genetically modified Bt crops by introducing Bt genes to plants through genetic engineering, thereby making the crops resistant to insect pests.
Another natural insecticide called pyrethrum, extracted from the flower head of chrysanthemum cinerariifolium, is used in organic farming practices. These plants grown near crops repel insects due to their insecticidal properties. Trichoderma, a free-living fungus, Baculoviruses of genus Nucleopolyhedrovirus in plant roots, acts as a bio-control agent for various plant pathogens and pests respectively.