One of the favourite arguments of the pro-GM lobby in support of Bt-toxin GM crops is that the Bt toxin has been safely used for decades by organic farmers.
Many thanks to Susan Pusztai for the following information which precisely delineates the very considerable differences between the use of Bt in organic farming and the use of the Bt toxin as a transgene in GM crops.
This should be read in conjunction with Arpad Pusztai's recent comments, posted to the ngin list, on the gut lesions which have been found in several animal feeding studies on GM crops.
Bt in organic farming:
The bt bacteria, commercially available for organic farming is a preparation of weakened or most often dead bacteria, which is sprayed only in the case of high insect infestation and only onto the affected area.
The bacterium inside the spray contains the pro-form of the so called bt toxin. This is not an active component, it needs to be tailored (cut to size) to produce the active bt toxin, which is effective as a pesticide.
When the insect eats the dead bacterium, the toxin is partially digested in the insect gut by proteolytic (cutting) enzymes and converted to active bt toxin. This is actually a lectin which binds to the gut wall of the insects and this interferes with the digestion/absorption of food, thereby preventing growth, maturation, reproduction.
The actual bacterium, which is not eaten by any insects, degrades in the light/sun/rain pretty fast (less than a day). The chances of pests developing resistance to it are very low indeed, since all the pests which are exposed to the toxin are affected by it.
NOTE! The ACTIVE TOXIN can only be found IN THE GUT OF THE INSECT.
Bt bacteria has no harmful effect on the environment as far as we know.
As far as human safety is concerned, the bacterium is only ever present on the surface of the plant and, if there were any remaining bacteria on the crop when it is prepared for consumption, it can be easily washed off.
There are several bt pro toxins produced by the different strains of bt bacteria. These active toxins are sequenced, patented and used by the different companies for their own GM bt-toxin transgenic crops.
Bt in GM crops:
The gene of one, or several of the active, trimmed toxin is transferred to the GM plant and will be synthesized in every single cell of the transgenic plant and the active toxin is being expressed by every cell, all the time. Therefore, the ACTIVE TOXIN IS IN EVERY PLANT CELL AND TISSUE, ALL THE TIME and cannot be washed off.
Pests are exposed to a low dose of the toxin in their environment all the time, which gives the best chances for developing resistance.
As far as safety is concerned, the active toxins are not easily degraded by gut enzymes and, since they are lectins, they all are very likely to bind to the wall of the mammalian/human gut.
The bt toxin is in the soil, in the plant, in the pollen, in the nectar -- in short, in every part of the plant which is used as human food or animal feed.
Is there any difference between the two applications? Or are they 'substantially equivalent'?