Bt Research 2025, Vol.16, No.3, 95-102 http://microbescipublisher.com/index.php/bt 97 different Bt toxins, setting up non-BT crop shelters, and monitoring pest resistance. These measures can extend the service life of Bt technology and help achieve sustainable pest management (Bravo and Soberon, 2008; Bravo et al., 2015; Soberon et al., 2015; Afzal et al., 2024). 3 Environmental Concerns Associated with Bt 3.1 Ecological risks Bt crops and sprays are highly targeted and have little direct impact on non-target organisms. Many field and laboratory studies have shown that Bt protein has no obvious toxicity to invertebrates, mammals and birds. Compared with chemical pesticides, Bt crops have lower negative effects on the ecology (Koch et al., 2015; Twardowski et al., 2022). Some negative effects occasionally found in the laboratory mostly do not occur in the field (Koch et al., 2015). In addition, the use of Bt crops reduces broad-spectrum pesticides, helps protect natural enemies, and also promotes biodiversity (Lu et al., 2012). However, it is still necessary to track the potential impact of Bt proteins on non-target organisms over the long term (Manjunath, 2020; Peterson et al., 2020). 3.2 Resistance development in target pests Although Bt crops can delay the development of resistance, pests may still develop resistance to Bt proteins. There have been reports of pests developing resistance to a single Bt protein both in the laboratory and in the field, especially when there is no "high-dose/sanctuary" strategy. To slow down resistance, comprehensive management is required, such as planting sheltered areas, superimposing different toxins and continuous monitoring. 3.3 Gene flow and biodiversity concerns from transgenic Bt crops The genes of Bt crops may be transmitted to wild relatives through pollen, which poses a risk of gene mobility. Most studies suggest that this risk is very low in crops such as corn and soybeans. However, in areas with wild relatives such as cotton, sales and cultivation need to be restricted to avoid gene outflow (Then and Bauer-Panskus, 2017; Peterson et al., 2020). In addition, the large-scale cultivation of Bt crops may also change the structure of field biodiversity, so it is necessary to continuously assess its role in the ecosystem. 3.4 Persistence in soil and water ecosystems Bt protein decomposes rapidly in the soil and is not easy to accumulate. Its impact on non-target organisms in the soil is limited. However, spray components such as Bt spores may persist in the soil for many years and sometimes have certain impacts on soil ecology. Compared with traditional pesticides, Bt protein poses a much lower risk of pollution to water and soil. However, attention still needs to be paid to long-term accumulation and persistence in extreme environments. 4 Strategies to Minimize Environmental Impact 4.1 Resistance management Resistance management is very important to ensure the long-term use of Bt crops. A common approach is the "high-dose/sanctuary" strategy. It is to grow some non-BT crops around Bt crops to provide living space for BT-sensitive pests, which can slow down the accumulation of resistance genes (Shelton et al., 2000; Carriere et al., 2016; Arends et al., 2021). Research has found that the size, location and distance of the sheltered area from Bt crops all affect the effect. If multi-toxin Bt crops are used together with sanctuary areas, resistance can be better delayed (Carriere et al., 2016; Arends et al., 2021) (Figure 2). In addition, some scholars have proposed releasing individual pests sensitive to Bt as a new approach, which may help reverse the trend when resistance increases. 4.2 Application practices The rational application of Bt crops can alleviate environmental pressure. Its promotion has greatly reduced the usage of chemical pesticides and also lowered the harm to the environment and human health (Cannon, 2000; Chatla and SumanthKumar, 2017). Through crop rotation, intercropping and diversified planting, resistance pressure can be dispersed and secondary pest outbreaks can also be avoided. Combining field monitoring and precise pesticide application, and adjusting according to the characteristics of local pests, can also improve the efficacy of Bt crops and reduce the impact on non-target organisms (Macintosh, 2010; Manjunath, 2020).
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