Field Crop 2024, Vol.7, No.5, 270-277 http://cropscipublisher.com/index.php/fc 274 bollworm was effectively eradicated from the region, and the efficacy of Bt cotton was restored. This case study highlights several key lessons: the importance of a strong science base, broad stakeholder support, rigorous implementation and monitoring, and the need for continuous improvement in resistance management practices. The success in the southwestern United States serves as a model for other regions facing similar challenges with Bt cotton and other transgenic crops (Carrière et al., 2019). 6 Advances in Resistance Management 6.1 Genetic approaches to enhance Bt cotton efficacy One innovative genetic approach to enhance Bt cotton efficacy involves hybridizing transgenic Bt cotton with non-Bt cotton. This strategy, tested over an 11-year field study in China, involves crossing Bt plants with conventional non-Bt plants and then sowing the second-generation seeds. This method results in a field mixture where three-quarters of the plants produce Bt protein and one-quarter do not. The presence of non-Bt plants promotes the survival of susceptible insects, thereby delaying the evolution of resistance in pests like the pink bollworm (Pectinophora gossypiella) (Wan et al., 2017; Tabashnik and Carrière, 2019). Additionally, understanding the genetic basis of resistance, such as identifying mutations in pest genes that confer resistance, can inform the development of more effective Bt crops. For instance, a dominant point mutation in the tetraspanin gene of the cotton bollworm (Helicoverpa armigera) has been linked to resistance, and tracking such mutations can improve resistance management strategies (Guan et al., 2020). 6.2 Development of new Bt varieties with multiple modes of action The development of new Bt cotton varieties that incorporate multiple modes of action is crucial for effective resistance management. Next-generation Bt crops often include pyramided traits, which combine multiple Bt toxins to target pests. This approach has shown promise in delaying resistance. For example, Bt cotton varieties producing Cry1Ac, Cry1Fa, and Vip3Aa have been effective against pests like Helicoverpa zea, which have developed resistance to other Cry toxins (Head and Greenplate, 2012; Yang et al., 2022). The use of multiple toxins ensures that even if pests develop resistance to one toxin, they are still susceptible to others, thereby maintaining the efficacy of Bt crops (Tabashnik et al., 2023). 6.3 Role of biotechnology in supporting resistance management Biotechnology plays a pivotal role in supporting resistance management by enabling the development of advanced Bt crops and facilitating the implementation of integrated pest management (IPM) strategies (Zhu and Luo, 2024). The use of biotechnological tools such as CRISPR/Cas9 for gene editing allows for precise modifications in pest genomes to study resistance mechanisms and develop countermeasures (Jin et al., 2018). Additionally, biotechnology supports the creation of structured and unstructured refuges, which are essential components of resistance management plans. For instance, the natural refuge strategy, which relies on the presence of non-Bt crops like soybean and maize, has been shown to be effective in managing resistance in pests like Helicoverpa zea (Arends et al., 2021). Moreover, the integration of biotechnological advancements with traditional IPM practices, such as the use of sterile insect techniques and crop rotation, can enhance the sustainability of Bt crops and delay resistance (Knight et al., 2021; Gassmann and Reisig, 2022). 7 Future Perspectives and Recommendations 7.1 Suggestions for improving current resistance management strategies To enhance the efficacy of current resistance management strategies for Bt cotton, several key improvements can be made. Firstly, integrating multiple Bt toxins with different modes of action can help delay resistance development. For instance, the combination of Cry1Ac and Cry2Ab has shown synergistic effects against resistant strains of Helicoverpa armigera, suggesting that pyramiding these toxins could prolong the efficacy of Bt cotton (Wei et al., 2015). Additionally, the use of Vip3Aa in combination with Cry toxins has been effective against Helicoverpa zea, indicating that incorporating Vip3Aa could be a valuable strategy (Yang et al., 2022). Another suggestion is the implementation of structured refuges, which has been successful in delaying resistance in various regions. For example, in the United States, planting non-Bt cotton refuges alongside Bt cotton has been effective in managing pink bollworm resistance. Similarly, in China, the use of natural refuges and seed mix
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