Bt Research 2025, Vol.16, No.4, 168-181 http://microbescipublisher.com/index.php/bt 172 In contrast, the EU is cautious about genetically modified crops and only approved the cultivation of a few Bt corn varieties in 1998. As of 2021, the area of Bt corn planting in the EU is less than 100 000 hectares, and it is mainly concentrated in some countries such as Spain. The EU's strict regulatory and labeling system and public concerns about genetically modified foods have hindered the promotion of Bt crops. The Chinese government has invested enormously in promoting independent research and development of Bt crops. In addition to commercialized Bt cotton, although the two Bt rice and one Bt corn strains approved in 2009 have not been widely promoted, they have laid the foundation for the subsequent industrialization of GMO staple foods. Since 2020, China has accelerated the pace of industrialization of crop biobreeding, and has successively obtained biosafety certificates for multiple independently developed Bt corn and Bt soybean varieties. 4 Main Bt Genetically Modified Crops and Their Applications 4.1 Bt cotton: the effectiveness and promotion of preventing and controlling cotton bollworms Cotton is one of the earliest and most successful applied crops for Bt genetically modified technology. Bt cotton usually carries the Cry1Ac or Cry2Ab genes from Bt bacteria, and can express toxic proteins in various parts of the cotton plant, and is highly toxic to Lepidopteran larvae such as Helicoverpa armigera. Field experiments and large-area planting results show that the control effect of Bt cotton on bollworms is extremely significant. Under the condition of no chemical insecticide application, the density of larvae of cotton bollworms in Bt cotton fields is more than 80% lower than that of non-Bt cotton fields, and the floc spit rate and fiber yield are significantly improved. After the promotion of Bt cotton in the Yellow River Basin cotton area in China, the risk index of cotton bollworms has dropped significantly, and the output per hectare increased by about 10%~20% compared with before the promotion. Due to its good anti-worm effect, farmers have reduced their dependence on chemical pesticides. According to statistics, China's Bt cotton planting has reduced the amount of pesticides in cotton fields by 50%~70%, which not only reduces the cost of prevention and control, but also protects the population of natural enemy insects in the fields (Lu et al., 2021). The direct economic benefits of Bt cotton are very considerable. At present, Bt cotton has been widely planted in more than a dozen cotton-producing countries including the United States, China, India, Australia, etc., accounting for more than 80% of the global cotton planting area (Quan and Wu, 2023). 4.2 Bt corn: the control effect on corn borer and root worms Corn is another major crop with widespread use of Bt technology. The initial target pest of Bt corn was the lepidoptera larvae such as the European corn borer (Ostrinia nubilalis), and later it also included the main underground insect of corn, the corn root worm (Diabrotica, Coleoptera). Common Bt corn varieties carry genes such as Cry1Ab, Cry1F, and Cry2Ab to prevent and control borer, or carry genes such as Cry3Aa and Cry3Bb1 to prevent and control rootworms (Siebert et al., 2012). Field application results show that the prevention effect of Bt corn on corn borers can reach more than 95%, and the damage of drilling and folding losses are significantly reduced. After planting Bt corn, the survival rate and feeding amount of corn borer larvae in the plant stems decreased significantly, and the fruiting rate and grain yield increased significantly. In the corn belt area of the United States, planting Bt corn for many years not only protects crops in genetically modified fields from insect borers, but also indirectly lowers the corn borer population base in surrounding non-Bt corn fields, achieving regional pest suppression. In addition, Bt corn also effectively controls the toxin pollution problem in corn fields - the serious harm of corn borers often leads to fungal infections and mycotoxin accumulation in the ears, while Bt corn significantly reduces the level of mycotoxins in the grains due to the reduction of insect pests, improving the safety of food quality. For underground pests such as corn rootworms, Bt technology provides a more environmentally friendly and efficient means than soil application (Gassmann et al., 2019). 4.3 Research and development progress of Bt soybean and rice Compared with cotton and corn, the research and development and promotion of Bt genetically modified soybeans and rice is relatively late, but important progress has also been made. Bt soybeans are mainly targeted at soybean heart worms and nocturnalis pests. Brazil was the first to commercialize the insect-resistant soybean variety (Intacta™) in 2013, which introduced the Cry1Ac gene, which can effectively prevent and control major
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