Bacillus thuringiensis (Bt)

What is Bt?

Bt is the abbreviated name given to the common bacterium Bacillus thuringiensis. Different strains of this bacterium produce a range of different crystal proteins that are toxic to different types of insects. Most are only toxic to Lepidopterans (butterflies and moths), Coleopterans (beetles) or Dipterans (flies) but some are toxic to more than one of these insect groups.
These crystal proteins are not toxic to any other insects or living organisms, including humans.
Bt has a long history of safe use as a natural insecticide that is used widely by the organic
food industry and in many developing countries to protect agricultural and forestry crops from insect pests. It has probably always been present (in trace amounts) in the human diet due to its common presence in soil and water and on the surfaces of plants.
Genes coding for Bt crystal proteins have recently been introduced into GM plants to protect them from insect attack.
The toxic effect of the Bt crystal proteins requires a particular gut environment and special gut receptors that are only present in some insects.The crystal proteins must be eaten by the insect larvae and converted into a toxic form by enzymes in the insect gut.The toxic protein then binds to specific receptors on the insect gut wall, leading to death of the cells lining the gut wall and paralysis of the gut. The insect stops feeding and dies.
A large number of scientific studies have shown that Bt is not toxic to humans or other
vertebrate animals. Rats, mice, rhesus monkeys and humans do not contain receptors for the toxin proteins.
There are several environmental concerns associated with the use of Bt in agriculture—
such as the possibility of toxic effects on beneficial insect populations and the possibility
that insects will become resistant to the action of Bt.These concerns are addressed by other government agencies before GM crops are allowed to be grown.