Bt is the term commonly used to indicate proteins extracted from a
bacterium (called Bacillus thuringiensis) which is present
naturally in the soil worldwide. This bacterium has long been used in
organic Bt insecticide preparations. A unique feature of this bacterium is
its production of crystal-like proteins that selectively kill specific
groups of insects. These crystal proteins (Cry proteins) are insect
stomach poisons that must be eaten to kill the insect. Once eaten, an
insect's own digestive enzymes activate the toxic form of the protein. The
Cry proteins bind to specific "receptors" on the intestinal lining and
rupture the cells. Insects stop feeding within two hours of a first bite
and, if enough toxin is eaten, die within two or three days.
Biotechnology has made it possible to use Bt proteins more effectively to
control insects that are harmful to crops.
The genes coding for these proteins are actually introduced into the
plant, enabling it to produce the protein continuously and so protect
itself against attacks from insect pests.
Benefits
ˇ Means of control for insect pests, which is more specific than
conventional insecticides;
ˇ Reduced usage of conventional insecticides (using Bt technology reduces
the need for recourse to conventional insecticides);
ˇ Reduced requirement for energy and for inputs associated with the use of
such products;
ˇ Means of insect control that is more environmentally friendly.
Benefits for the environment
ˇ The Bt proteins act on a narrow range of insects (Lepidoptera only) and
are therefore very unlikely to harm non-target species.
ˇ Conventional crop protection agents allow control of many different
insect pests, but are also somewhat toxic to certain non-target species.
ˇ Using more selective means of controlling insects, such as Bt transgenic
crops, has environmental advantages. In addition, the reduced usage of
conventional synthetic insecticides leads to reduced consumption of energy
and of the inputs needed for their manufacture, packaging, transport and
storage.
Benefits for farmers
ˇ Crops expressing Bt proteins offer farmers an environmentally friendly
way to control insect pests.
ˇ The use of Bt crops avoids the need to handle chemical insecticides.
These are perfectly safe if handled properly, but can be a hazard if used
incorrectly or spilt.
ˇ In contrast, there is enough toxicological data from Bt cotton crops to
show that there is probably no risk associated with use of the Cry1Ac
delta-endotoxin from Bacillus thuringiensis or with the genetic
material needed to produce these Bt plants.
ˇ This is a realistic solution for farmers when it comes to insect
control.
Current situation
ˇ Bt insecticides have already been used for 60 years, and are permitted
for use by
organic farmers.
ˇ Crops incorporating the Bt technology first went on sale in 1996, in the
form of cotton protected against a caterpillar pest.
ˇ Bt technology is available for crops of cotton, fodder maize and sweet
corn and
potatoes.
Photographs 1: Conventional cotton damaged by an insect pest (left)
and a cotton plant protected against the insect as a result of Bt
technology (right).
Sources
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Source: Europabio
