Mechanisms and molecular genetics of insect resistance to insecticidal proteins from Bacillus thuringiensis

Insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) are used globally as bioinsecticides and in genetically engineered Bt crops to manage key insect pests. Transgenic Bt crops have been cumulatively planted on more than 1.5 billion hectares for more than 27 years, providing enhanced pest suppression, improved yields, increased farmer profits, and reduced environmental and health risks associated with the decreased use of conventional chemical insecticides. These benefits are reduced or lost when pests evolve resistance to Bt toxins in the field. Understanding the molecular genetic basis of resistance can be useful for monitoring, managing, and countering pest resistance to Bt crops. To date, 26 cases of field-evolved practical resistance and 18 cases of early warning of resistance to Bt crops have been reported, but the molecular genetic basis is known for only 9 of the 44 resistance cases to Bt crops. Here, we provide a comprehensive update on the molecular genetic mechanisms for these nine cases of field-evolved resistance to Bt crops and the numerous cases of laboratory-selected resistance to Bt toxins. We highlight lab-selected resistance involving regulation of Bt receptor genes and how recent research shows that regulatory pathways can be coopted to cause resistance. We further review recent technological advances in genomics and reverse genetics that have improved our ability to monitor and understand of the molecular genetic basis of pest resistance. The findings outlined here describe not only the complex genetic nature of Bt resistance, but also highlights new areas of exploration into the fundamental evolutionary basis of resistance mechanisms, which are important for sustaining the efficacy of currently available and future transgenic Bt crops.