Biocontrol agents

Biocontrol is the use of biological methods to control plant diseases and pests. The chemical insecticides, pesticides and weedicides used instead are toxic to humans and animals and pollute soil, ground water and crops.

Organic farming relies on natural predation and holds that biodiversity furthers health: a varied landscape is more sustainable, and pests are kept at manageable levels by checks and balances instead of being wiped out.

Eradicating pests is seen as undesirable, since the useful predatory and parasitic insects that feed on them or use them as hosts would then die out. Knowing the field's predators and pests, their life cycles, feeding and habitats, helps design biocontrol.

Ladybird beetles (red and black) control aphids, and dragonflies control mosquitoes.

The bacterium Bacillus thuringiensis (Bt) controls butterfly caterpillars. Its dried spores, sold in sachets, are mixed with water and sprayed on plants such as brassicas and fruit trees.

When larvae eat the spores, the toxin is released in their gut and kills them, while other insects are unharmed. Genetic engineering has put Bt toxin genes into plants such as Bt-cotton, making them resistant to insect pests.

The free-living fungus Trichoderma, common in root ecosystems, is being developed to treat plant disease; its species control several plant pathogens.

Baculoviruses attack insects and other arthropods; most used in biocontrol belong to the genus Nucleopolyhedrovirus. They are species-specific and narrow-spectrum, with no harm shown to plants, mammals, birds, fish or non-target insects, which suits integrated pest management (IPM) and ecologically sensitive areas.