Molecular Entomology 2024, Vol.15, No.5, 200-208 http://emtoscipublisher.com/index.php/me 203 4.4 Analysis of results: success and challenges The implementation of Bt cotton in Gujarat, India, initially brought significant success in controlling pink bollworm populations and reducing reliance on chemical insecticides. The Cry1Ac and Cry2Ab proteins expressed by Bollgard II® cotton were effective in reducing bollworm infestations and increasing yields. However, the success of Bt cotton was challenged by the emergence of resistance in pink bollworm populations, as reported in multiple studies from India. This resistance, particularly to Cry1Ac, posed a major threat to the sustainability of Bt cotton as an effective pest control tool (Naik et al., 2018). The key challenge identified was the inadequate implementation of resistance management strategies. Non-compliance with refuge planting by farmers was one of the major reasons for the accelerated development of resistance, as refuges are crucial for maintaining populations of susceptible pests. Additionally, poor adoption of Integrated Pest Management (IPM) practices, such as shorter cotton seasons and destruction of crop residues, exacerbated the problem (Tabashnik and Carrière, 2019). Despite these challenges, the use of pheromone traps and targeted insecticide applications provided some level of control over bollworm populations. Pheromone-based monitoring, when combined with foliar insecticides, successfully reduced bollworm densities and boll damage in several regions (Carrière et al., 2017). 4.5 Lessons learned from the case study Several important lessons can be drawn from the management of cotton bollworms in Bt cotton fields in Gujarat. While Bt cotton is an effective tool for pest control, its long-term success depends on the rigorous implementation of resistance management strategies. Compliance with refuge planting, shorter cotton seasons, and IPM practices are essential to prevent the rapid development of resistance among pest populations (Mohan and Komarlingam, 2017). The use of complementary pest management strategies, such as pheromone traps and selective insecticide applications, is crucial in maintaining pest control efficacy (Figure 1) (Tabashnik et al., 2020). Integrating non-chemical methods into pest management strategies, such as the use of pheromone-based mating disruption, can reduce dependence on Bt proteins and extend the life of genetically modified crops (Sreenivasa et al., 2021). Figure 1 Management strategies (Adopted from Tabashnik et al., 2020) Image caption: (A) The refuge strategy is the primary approach adopted worldwide to delay the evolution of pest resistance to Bt crops and was used in Arizona from 1996 to 2005. Refuges of non-Bt cotton planted near Bt cotton produce abundant susceptible moths (blue) to mate with the rare resistant moths (red) emerging from Bt cotton. If the inheritance of resistance to Bt cotton is recessive, as in pink bollworm, the heterozygous offspring from matings between resistant and susceptible moths die when they feed on Bt cotton bolls as larvae (24). (B) Bt cotton and sterile moth releases were used together in Arizona from 2006 to 2014 as part of a multitactic program to eradicate the pink bollworm. Susceptible sterile moths (brown) were released from airplanes to mate with the rare resistant moths emerging from Bt cotton. The few progeny produced by such matings (48) are expected to be heterozygous for resistance and to die when they feed on Bt cotton bolls as larvae (Adopted from Tabashnik et al., 2020)
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