Bt Research 2025, Vol.16, No.4, 125-135 http://microbescipublisher.com/index.php/bt 128 of Bt enhanced preparations and Bt modified strains. For instance, when Bt is used in combination with other microbial preparations or with modified Bt toxins (such as Vip3Aa mutants), the toxicity to major pests (such as armyworms and cotton bollworms) can be significantly enhanced - in laboratory tests, Its virulence is 8 times higher than that of natural Bt protein (Yang et al., 2022; Chang et al., 2024). These experiments also show that mixing different components together or using modified toxins can reduce the amount of Bt required to kill pests. This indicates that transgenic Bt has improved in both the types and effects of pest control (Figure 1). Figure 1 Histopathological effects on the midgut tissue of third-instar S. frugiperda larvae (Adopted from Chang et al., 2024) Image caption: (a) non-treatment, (b) Bacillus thuringiensis subsp. kurstaki (Bt), (c) detail of the section from the single treatment with Bt, (d) Photorhabdus luminescens (Pl) ATCC 29 999 in whole broth (after 120 h of incubation), (e) detail of the section from the single treatment with Pl ATCC 29 999, (f) Pl 2103-UV in whole broth (after 120 h incubation), (g) detail of the section from the single treatment with Pl 2103-UV, (h) combined treatment of Pl ATCC 29 999 and Bt (mixed at a ratio of 1:5), and (i) combined treatment of Pl 2103-UV and Bt (mixed at a ratio of 1:5). Scale bar = 90 µm. Am, apical membrane; Bm, basal membrane; Lu, lumen; N, nucleus; V, vesicle formation (Adopted from Chang et al., 2024) In addition, laboratory studies have found that treating Bt toxins with encapsulation technology or adding substances that can promote biofilm formation can help Bt toxins resist environmental damage, thereby enhancing the control ability for more pests (Jalali et al., 2023; Zhao et al., 2025). These methods can not only directly increase the toxicity of Bt, but also enable Bt products to maintain their activity for a longer time under experimental conditions simulating harsh environments. 4.2 Field trials, long-term effect evaluation and drug resistance management Field trials are crucial for verifying laboratory results and confirming the practical application effects of improved Bt products. Studies have shown that mixing Bt with bacterial metabolites that can inhibit insect immunity, or using Bt products with optimized formulas, can achieve good control effects in both greenhouse and field environments, especially against lepidoptera pests such as noctuids and armyworms (Hrithik et al., 2022; Chang et al., 2024). These results prove that under different environmental conditions, the improved Bt formula can control pests more stably and effectively. Long-term field monitoring can also assess whether strategies for managing pest resistance can be used in the long term. Research has found that growing Bt crops, using Bt products that can express multiple toxins, or employing crops with novel modes of action can delay the development of pest resistance in actual environments - especially when these methods are used in combination with "refuge strategies" and integrated pest management measures, the effect is more obvious. These methods can help Bt technology remain effective throughout multiple growing seasons.
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