Emergence of New forms of resistance and secondary pest and weed problems
Resistance had already emerged on a very large scale in modern agriculture even before the emergence of GMO's (Georghiou 1986).
There are now 500 species of insect, mite or tick resistant to one or more compounds together with more than 400 herbicide resistant weed biotype and 150 resistant fungi and bacteria (Vorly,1998,Heap,2000).
Evolution of resistance can occur in the context of (1) GM crops expressing an insecticidal product eg Bt maizc leading to the insect resistance or (2) GM crops leading to overuse of herbicides, leading to weed resistance.
These are the risks which should be taken into account and safety measures implement.