Bt Research 2025, Vol.16, No.4, 168-181 http://microbescipublisher.com/index.php/bt 173 lepidopteran pests (such as soybean squid, fall armyworm, etc.) (Huang, 2020). The planting results show that Bt soybeans have reduced 2~3 chemical pesticide sprays and increased yields, achieving economical and effective control of pests. As of 2020, the area of converted Bt soybeans in Brazil and Argentina has accounted for more than 20% of the total soybean area in the country, showing good application prospects. China also approved the first independently developed safety certificate for the insect-resistant genetically modified soybean strain in 2020, paving the way for the commercialization of Bt soybeans. Bt rice is another crop that has attracted much attention. The main pests of rice such as erectile borer and rice leaf rolling borer seriously threaten rice yield. The Chinese scientific research team conducted Bt rice research in the 1990s and cultivated several anti-borer rice lines containing the Cry1Ab/Ac fusion gene. Among them, "Huahui No. 1" and its hybrid rice "Bt Shanyou 63" have been tested for many years and have confirmed that they are extremely resistant to borer borer, which can reduce the sheath rate of borer borer by more than 80%, and increase the average yield by 5%~8% (Li et al., 2012). These two Bt rice lines received biosafety certificates in 2009, marking the world's first genetically modified insect-resistant variety for staple food crops. 4.4 Case analysis: promotion and application of Indian Bt cotton and Brazilian Bt corn India is one of the world's largest cotton producers. For a long time, cotton bollworms have caused significant losses in Indian cotton fields. In 2002, the Indian government approved the commercialization of Monsanto's Bt cotton hybrids, which is the first time that India has introduced genetically modified crops. Bt cotton is being promoted in India very quickly: the planting area jumped from less than 500 000 hectares in 2003 to nearly 10 million hectares in 2011, accounting for more than 90% of the country's cotton fields. Bt cotton effectively controlled the outbreak of cotton bollworms, increasing the yield of Indian cotton by about 50% within ten years, and reducing the amount of pesticides by more than half. Many small farmers reported that the cotton harvest was more stable and the income increased after planting Bt cotton. Brazil is the world's second largest corn exporter, with pests such as corn borer and fall armyworm raging all year round. Brazil approved the first Bt corn variety in 2008 to introduce the Cry1Ab gene to prevent and control corn borer. Since then, various Bt corns containing Cry1F, Cry2Ab and anti-root wormCry3Bb1 have been approved, so that Brazilian corn can achieve genetically modified prevention and control of major pests on the ground and underground. Bt corn has been promoted smoothly in Brazil. By 2018, the proportion of genetically modified corn cultivation exceeded 85%. The cultivation of Bt corn has greatly reduced the use of organophosphorus and pyrethroid insecticides in Brazilian corn fields, and farmers no longer need to apply medicine frequently, and the production costs are reduced while the operating environment is safer (Burtet et al., 2017). Especially in tropical areas, fall armyworms often cause devastating insect disasters. Since the adoption of new Bt corn containing Vip3A toxic protein, the insect has been effectively suppressed and corn yields have been steadily increased (Moscardini et al., 2020). The Brazilian government and scientific research institutions also closely monitor pest resistance dynamics and promote resistance management strategies, such as planting 5% to 10% of non-Bt corn as shelter. 5 Field Performance and Yield Benefits 5.1 Effects of pest control and reduction of pesticide use The most direct field performance of Bt genetically modified crops is the excellent target pest control effect and the significant reduction in the use of chemical pesticides. Taking Bt cotton as an example, experiments show that its field control rate of the main target pest cotton bollworm is often above 90%, which is significantly better than conventional spray fields. After planting Bt cotton, most cotton farmers only need to spray pesticides 12 times a quarter or even no medicine, while traditional cotton fields often need to spray 68 times. According to statistics, in the northern cotton area of China, the large-scale promotion of Bt cotton has reduced the use of pesticides in cotton fields by about 80%, and the risk of pesticide residues has also been reduced accordingly (Qiao and Huang, 2018). In addition to cotton, after promoting Bt varieties on corn, there is basically no chemical pesticides to prevent and control heartworms such as corn borers. Therefore, the amount of pesticides used in corn fields in the United States and other countries has decreased by 45% to 60%. Large-area Bt crop cultivation also produces an
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