Molecular Entomology 2024, Vol.15, No.5, 200-208 http://emtoscipublisher.com/index.php/me 204 The case highlights the importance of continuous monitoring and early detection of resistance development. Monitoring resistance alleles and ensuring early interventions can help mitigate the risks posed by resistant pest populations (Wang and Lin, 2024), as seen in the management efforts in the United States, where pink bollworm was successfully eradicated through a combination of Bt cotton and sterile moth releases (Tabashnik et al., 2020). 5 Resistance Development in Cotton Bollworms 5.1 Mechanisms of resistance to Bt toxins The primary mechanism of resistance in pink bollworm (Pectinophora gossypiella) to Bt cotton lies in genetic mutations. These mutations often occur in the cadherin gene and ATP-Binding Cassette (ABC) transporters, disrupting the binding of Bt toxins (e.g., Cry1Ac and Cry2Ab) to the insect gut receptors, thereby reducing their efficacy (Wang et al., 2022). Cross-resistance is another issue, as resistance to one Cry protein can sometimes extend to another (Wei et al., 2015). 5.2 Factors contributing to resistance evolution Several factors drive the evolution of resistance, including continuous exposure to Bt toxins without effective refuges. In regions like India, non-compliance with structured refuge planting has accelerated resistance development, as seen with widespread pink bollworm resistance to Cry1Ac and Cry2Ab toxins (Tabashnik and Carrière, 2019). Additionally, the high reproductive rate of cotton bollworms and their genetic adaptability contribute to the rapid evolution of resistance (Akhtar et al., 2018). 5.3 Monitoring resistance in field populations Monitoring the prevalence of resistance alleles is crucial for early intervention. In China, DNA-based screening revealed that mutations in the cadherin gene were associated with Cry1Ac resistance in pink bollworm populations (Wang et al., 2020). Similar mutations in the ABC transporter gene (PgABCA2) have been documented in resistant strains from India and Arizona, indicating that resistance mechanisms are consistent across regions (Mathew et al., 2018). 5.4 Strategies to delay resistance development Implementing strategies to delay resistance development is essential for the sustainability of Bt cotton. One effective approach is the use of "pyramided" Bt crops that express multiple toxins, reducing the likelihood of resistance development to all toxins simultaneously. Additionally, integrating Bt cotton with non-Bt refuges, as practiced in China, has successfully delayed resistance evolution by maintaining susceptible pest populations (Wan et al., 2017). Monitoring resistance at the molecular level, along with adopting shorter cotton-growing seasons, has proven to be effective in managing resistance in other regions (Chen et al., 2017). 6 Integrated Pest Management (IPM) Approaches 6.1 Role of Non-GM crops in IPM for cotton bollworms Non-GM crops play a crucial role in IPM strategies by serving as refuges that slow the evolution of resistance in bollworm populations. For instance, planting non-Bt cotton alongside Bt cotton allows the survival of susceptible pest populations, reducing the selection pressure for resistance. Research in India emphasizes that compliance with refuge planting has a significant impact on delaying resistance and enhancing the long-term efficacy of Bt cotton (Rakhesh et al., 2023). 6.2 Use of biopesticides in combination with Bt cotton The integration of biopesticides, such as neem-based formulations and Bacillus thuringiensis (Bt) sprays, with genetically modified cotton strengthens pest control strategies. In a study from Telangana, India, combining Azadirachtin sprays with pheromone traps demonstrated reduced pest damage and higher yields (Alugoju et al., 2022). This approach minimizes chemical pesticide use and supports ecological sustainability. 6.3 Cultural and mechanical control strategies Cultural practices, such as early sowing and crop rotation, are essential components of IPM. For example, removing and destroying plant residues disrupts the pest's lifecycle, reducing overwintering populations. Studies
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