The present invention discloses Resistance Management (RM) practices that are critical to safeguard Bacillus thuringiensis as a natural resource and sustain genetically modified corn expressing Bt toxins as a suitable method for ECB and WCRW management. A useful tool in developing RM strategies is to develop laboratory selected colonies that exhibit high levels of resistance to a particular toxin. The availability of selected strains allows determination of the genetic expression of resistance (i.e., dominant vs. recessive, autosomal vs. sex-linked) and whether or not the resistance mechanism is specific for a given toxin. In addition, the availability of resistant strains will allow estimation of the particular resistance allele frequency in the field, and provides a tool to identify the biochemical and physiological basis of resistance and a means to develop molecular probes to monitor the evolution of resistance in the field.