Bt Research 2025, Vol.16, No.4, 157-167 http://microbescipublisher.com/index.php/bt 164 toxins. Field trials have shown that the effect of Bt preparations mixed with low-dose avermectin against bollworms is significantly better than either alone, and that the residual and resistance pressure of chemicals is reduced due to the reduced dose (Narkhede et al., 2017). This is a "supportive" strategy: Bt is responsible for the main insecticide, chemical drugs play an auxiliary role in increasing efficiency, and can provide a certain damage control effect when the Bt's effectiveness decreases to prevent fluctuations in the treatment effect. Secondly, the cooperation between Bt and predatory natural enemies/parasitic wasps: biological control measures can also cooperate with each other, such as releasing Bt bacteria agents and red-eyed bees at the same time in cotton fields. The two act at different stages of pest occurrence, achieving full control. Practice has proved that in the comprehensive management of cotton bollworms, the addition of Bt bacteria can reduce the density of surviving larvae, which improves the subsequent parasitic efficiency of parasitic bees (Abbas, 2020), while red-eyed bees reduce the egg density of field insects and reduces the burden of Bt prevention and control. The combined effect of cotton field pest control is about 15% higher than that of separate measures, and the economic cost is controllable. Third, Bt is combined with agronomic prevention and control methods: for example, implementing the combination of Bt biopesticides with insect-induced lamps and sex pheromones on vegetables. The insect-induced lights at night lures and kills adults, reducing the amount of egg laying in the field, while the Bt spray during the day kills larvae. The two are complementary in time, which can control the density of pest population to a lower level. 7 Safety and Risk Assessment 7.1 Considerations on ecological risks and environmental release of transgenic Bt strains Before applying synthetic biologically modified Bt strains to the field, their ecological environment safety must be fully evaluated. The engineered Bt strain may have stronger environmental adaptability than the wild type, such as resistance to ultraviolet rays, temperature changes, etc. This means that once released into the environment, they may survive longer and spread more widely in soil or water bodies (Li et al., 2022). Engineering Bt strains usually carry exogenous gene modules, and it is necessary to evaluate whether these genes will be transferred to other microorganisms in the environment through plasmid ligation, transposons, etc. Once horizontal transfer occurs, unexpected ecological consequences may be brought. Bt toxins themselves are safe for most non-target biologics, but whether high-level releases accumulate and affect the ecosystem must be carefully evaluated. Especially in soil ecology, Bt spores and toxic proteins may remain, and the long-term impact on non-target organisms such as decomposed agents and pollinators needs to be analyzed and experimentally observed through food networks. Studies have shown that long-term planting of Bt gene crops will accumulate Bt toxic proteins in the soil, but they can generally be degraded under the action of soil organic matter, and there is no obvious negative effect on soil biome (Stotzky, 2000). 7.2 Effects on non-target organisms and soil microbial communities One of the key points of safety assessment of Bt strains is the potential impact on non-target organisms (such as beneficial insects, pollinating insects, aquatic organisms, etc.) and soil microbial communities. A large number of studies have shown that Bt toxin has no direct toxic effect on most non-target insects (bees, predator mites, natural ladybugs, etc.). However, engineering Bt strains may secrete higher contents or more species of toxins, and whether they will have an indirect effect on non-targets through the food chain needs attention. The Bt preparation may drift into the water body. It is known that the Israeli subspecies Bt (Bti) is used to control mosquitoes, which has a certain impact on non-target aquatic insects such as chiropra larvae, but the overall ecological effect is controllable. For those who transform Bt, if they have stronger environmental retention, their attenuation in the aquatic environment and their toxic effects on aquatic organisms should be evaluated. Soil is one of the main destinations of Bt spores. Studies have shown that Bt spores can remain in soil for weeks to months, but do not significantly disturb soil microbial diversity (Duan et al., 2025). However, engineered Bt strains may carry metabolic modifications, such as the melanin pathway, and whether introduced metabolites affect indigenous microorganisms is worthy of attention. Engineering Bt often carries antibiotic resistance genes
RkJQdWJsaXNoZXIy MjQ4ODYzNA==