February 2016
‘Bt’ insecticides are proteins produced by soil bacteria which have been used, as sprays, in organic farming for many years. They, therefore, arrived in their novel form inside GM crops complete with an existing reputation for long-term safe use by people who care about nature.
The safety of the artificial 'Bt' toxins as generated by GM crops is also based on their claimed species-specificity. Due to unique properties of the Bt protein, conventional wisdom says that it only becomes harmful if it can bind to receptors specific to the surface of the targeted pest gut-cells. Once bound, the toxin creates pores in the gut allowing its contents to leak out into the pest's body with lethal consequences. In any other animal, Bt protein is digested just like any other dietary protein.
Because regulators have accepted these claims, and because it's a useful, green-sounding selling point, and because pest-specificity avoids any need for tests on other animals, the biotech industry is very keen to maintain the belief in this limited toxicity of its Bt toxins.
However, Swiss environmental scientists have seriously questioned how much is actually known about Bt proteins.