Plants expression genes encoding -endotoxins from Bacillus thuringiensis (Bt) have triggered interest for the control of insect pest. Numerous plant species have been transformed with genes encoding various toxins. The first transformation experiments conducted with bacterial genes showed that their level of expression in plants is too low to confer adequate protection. To circumvent these problems, Bt toxins genes have been modified or resynthetized, dramatically improving their level of expression and the protection afforded. Despite these improvements, problems remain : the control of less susceptible insects and the durable deployment of transgenic plants have yet to be fully addressed.