Bt Research 2024, Vol.15, No.1, 1-9 http://microbescipublisher.com/index.php/bt 5 environmental friendliness. Compared with synthetic pesticides, B.t. strains grow and exist in the natural environment on the same day, without causing long-term pollution to the environment and ecosystem. B.t. strains have low toxicity to non-target organisms, minimal impact on humans, natural predators, and other beneficial insects, which is more conducive to maintaining ecological balance (Rajesh et al., 2018). However, the application effect of B.t. strains is affected by various factors. Among them, application methods, treatment doses, application time, and environmental conditions are important influencing factors. The appropriate application time and dose are key to ensuring effective control of pests. At the same time, environmental factors such as temperature, humidity, light, etc. can also affect the growth and effect of B.t. strains. In practical applications, these factors need to be comprehensively considered, and the application time and dose need to be reasonably selected to maximize the control effect of B.t. strains. 3.4 The application and research results of B.t. strains in the control of Phenacoccus solenopsis B.t. strains, as a kind of Gram-positive bacteria, can produce insecticidal crystal proteins called δ-endotoxins, which are toxic to multiple Lepidoptera, Diptera, and Coleoptera pests. Among them, B.t. kurstaki and B.t. texensis are the two most widely studied strains (Heckel, 2020). Taking B.t. kurstaki as an example, its control effect on Phenacoccus solenopsis has been widely studied. Studies have shown that the δ-endotoxin produced by this strain has high toxicity to the larvae of Phenacoccus solenopsis and can effectively control its population. Further studies have shown that during the process of combating Phenacoccus solenopsis, genes related to the synthesis of insecticidal crystal proteins in the genome of B.t. kurstaki have evolved to better adapt to the biological characteristics of Phenacoccus solenopsis. Additionally, B.t. texensis has also been used as a biopesticide to combat Phenacoccus solenopsis. Unlike B.t. kurstaki, the δ -endotoxin produced by B.t. texensis is also toxic to adults of Phenacoccus solenopsis. Studies have shown that some strains of B.t. texensis produce a new insecticidal crystal protein that is highly toxic to both adults and larvae of Phenacoccus solenopsis. Although B.t. has shown great potential in combating Phenacoccus solenopsis, as resistance to B.t. increases, its control effect may decline. Therefore, further research on the genetic evolution of B.t. is needed to develop more effective biopesticides to combat Phenacoccus solenopsis. 4 Genomics Analysis and Gene Evolution Research of Different B.t. strains 4.1 The relationship between gene evolution and resistance to scale insects There is a close relationship between the gene evolution of different B.t. strains and their resistance to scale insects. The resistance of B.t. strains to scale insects is determined by the specific genes or anti-insect factors carried by them. These anti-insect factors encode toxin proteins that target the pests, such as δ-endotoxins. They affect the normal physiological functions of the pests by acting on their digestive systems, leading to their death (Jin et al., 2018). The gene evolution of B.t. strains is related to their resistance to scale insects because it directly affects their virulence and resistance levels. In the natural environment, pest populations continuously interact and evolve with B.t. strains. Pests gradually develop resistance to the toxins of B.t. strains through genetic variation and selection adaptation strategies. This leads to the emergence of resistant pest populations and challenges the anti-insect effect of B.t. strains. To cope with the development of pest resistance, researchers are constantly working to select and modify B.t. strains with new anti-insect mechanisms. By using genetic engineering techniques, people can introduce anti-insect-related genes into B.t. strains or adjust the expression levels of existing genes to enhance their virulence and resistance. These modified B.t. strains can produce stronger toxic effects on newly emerged resistant pest populations, helping to continuously and efficiently control pests.
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