Bt Research 2025, Vol.16, No.2, 70-78 http://microbescipublisher.com/index.php/bt 73 among strains more obvious (Berçot et al., 2023). Studies have found that Bt adapts to local environmental stress and forms many different genotypes and functional types in different ecosystems. 4.2 Insect host diversity and co-evolutionary pressures The diversity and quantity of insect hosts will also strongly affect the genetic diversity of Bt. Bt is an insect pathogen. Its toxin genes, such as cry and cyt genes, are closely related to the species and ecological niche of the host insect. The changes in insect populations, host specificity, and the pressure of coevolution all lead to the continuous evolution of Bt, generating new toxin genotypes to counter the defense mechanisms of different hosts (Mishra et al., 2017). Human activities have led to a rapid increase in the population of some insects and provided new ecological niches for Bt, accelerating the coevolution and genotype innovation between Bt and its host (Argôlo-Filho and Loguercio, 2013; Gillis et al., 2018). 4.3 Human agricultural practices and pesticide use impacts Human agricultural activities, especially the extensive use of Bt biopesticides and the alteration of crop planting structures, have a significant impact on the population structure and genetic diversity of Bt. Long-term application of Bt preparations and cultivation of genetically modified crops will exert selective pressure on Bt populations in nature, causing certain genotypes to expand or new genotypes to emerge (Sorokan et al., 2023). In agricultural ecosystems, the interactions between Bt and plants, other microorganisms, as well as the frequent transfer of plasmids and mobile genetic elements, will also accelerate the genetic recombination and diversity increase of Bt (Gillis et al., 2018). Crop types and management measures in different regions can also affect the distribution and genotype composition of Bt (Berçot et al., 2023). 5 Functional Implications of Genetic Diversity 5.1 Variation in insecticidal toxin genes (Cry, Cyt, Vipfamilies) The insecticide toxin genes of Bt strains are very diverse. The main gene families include Cry, Cyt and Vip. Bt strains from different environments often carry multiple genes such as cry1, cry2, cry11, vip3A/B, cyt1, and cyt2. The combination of these genes determines which insects they can kill, such as pests of Lepidoptera, diptera or hemiptera (Berçot et al., 2023; Cao et al., 2025). For instance, strains carrying the cry1 andcry2 genes have a very good killing effect on lepidoptera pests. The cry11 and cyt genes are associated with virulence in killing diptera insects such as mosquitoes (Vilas-Bôas and Lemos, 2004; Navya et al., 2021). Researchers also discovered novel toxin genes, such as the tpp family, further enhancing the insecticidal mechanism and application potential of Bt (Cao et al., 2023). The evolution of toxin protein structure and the changes in functional regions also give Bt an advantage when adapting to different pests (Das et al., 2021; Yilmaz et al., 2024). 5.2 Correlation between genetic subpopulations and virulence traits Different genetic subgroups of Bt, such as different MLST types, fingerprint types or serotypes, are closely related to their virulence traits. Studies have found that some specific subgroups of Bt strains carry specific toxin gene combinations and are particularly lethal to certain pests (Berçot et al., 2023; Blackburn et al., 2023). For instance, strains with cry1 and cry2 genotypes achieved a 100% fatality rate against lepidoptera pests in experiments (Mishra et al., 2017; Navya et al., 2021). Some subgroups of Bt strains are only effective against diptera or hemiptera pests (Cao et al., 2023; Cao et al., 2025). The genotype and virulence type distribution of different subgroups are also influenced by geographical, ecological and host factors. Some subgroups also carry genes such as enterotoxins and meningitoxins, which may affect their ecological adaptability and potential risks (Biggel et al., 2022). 5.3 Resistance evolution and ecological adaptation The genetic diversity of Bt provides a basis for its evolution in pest resistance and ecological adaptation. The development of resistance by pests to Bt toxins is one of the main threats to the long-term sustainability of biological control. The Bt strain can effectively delay the resistance evolution of pests by constantly emerging new toxin genes and toxin structure changes (Das et al., 2021; Navya et al., 2021). Gene recombination, plasmid transfer and acquisition of new genes also enable Bt to adapt to different ecological environments and host
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