Detection and Mechanisms of Resistance Evolved in Insects to Cry Toxins from Bacillus thuringiensis

Transgenic crops producing Bacillus thuringiensis Cry toxins (Bt crops) have been planted globally to control some key pests. Benefited from implementation of proactive resistance management strategies such as the refuge strategy and the pyramid strategy in many countries, most of the target pests of Bt crops have been sustainably and effectively controlled for nearly 20 years. However, several cases of field-evolved resistance to Bt corn and Bt cotton have been documented, causing reduced field efficacy. Evolution of resistance by target pests is a real threat to the continued success of Bt crops. It is crucial to employ sensitive detection methods to monitor the evolution of the resistance in the target insects and thereby adapt resistance management strategies proactively to delay resistance evolution. Recent progress and considerations were reviewed on the four resistance detection approaches: concentration-response assay, F-1 screen, F-2 screen and DNA screen. Diverse genetic options for target pests to cope with Bt crops are challenging the efforts to understand mechanisms of resistance and to design rational resistance management strategies. Understanding the molecular genetic basis of Bt resistance is essential for developing sensitive resistance detection methods and intelligent resistance management strategies. Clarifying resistance mechanisms have facilitated and advanced our understanding on modes of action of Bt Cry toxins. The most recent advances on resistance mechanisms to Bt toxins are summarized in both laboratory-selected strains and field-evolved populations. According to current knowledge of Bt resistance mechanisms, some implications for resistance management and directions for future research are suggested.