Bt Research 2025, Vol.16, No.5, 204-213 http://microbescipublisher.com/index.php/bt 205 this basis, this study looks forward to future research directions and application prospects, aiming to provide reference for building an efficient, stable and ecologically friendly sustainable pest control system. 2 The Mechanism of Action and Application Status of Bt 2.1 Molecular mechanism and specificity of Bt toxin Bt can produce crystal toxins with insecticidal activity (mainly Cry proteins) that have a highly specific toxic effect on insects of specific orders. Its molecular mechanism of action can be summarized as: when the target insect feeds on a preparation containing Bt spores or crystals, the crystal toxin is dissolved in the alkaline midgut environment of insect larvae and is partially hydrolyzed by midgut protease into active toxin fragments. The activated Cry toxin can recognize and bind to specific receptor proteins on the surface of the cell membrane of the midgut epithelial cell, and the toxin is then inserted into the cell membrane and forms a pore (Myint et al., 2021). This duct destroys the osmotic pressure balance of epithelial cells, resulting in cell lysis, damage to midgut tissue, and death of insects due to digestive dysfunction and septic infection. Due to the differences in the midgut receptor structure of different insects, different Bt toxins have strong target selectivity for the killing spectrum of insects. Long-term practice and experiments have also proved that whether spraying Bt preparations or planting genetically modified crops containing Bt proteins has no adverse effects on humans, animals and natural enemies and insects. 2.2 Application model and success stories of Bt preparation As a biological pesticide, Bt preparations have been widely used in agricultural and forestry pest control around the world. Common Bt products include wettable powders, suspensions, granules, etc., which can be applied to the crop surface by spraying or sprinkling. In the vegetable field, Bt kurstaki-type preparations are used to prevent and control lepidopteran pests such as cabbage and diamondback moth, achieving significant insect reduction effects, and are widely used in organic agriculture. In forestry, Bt preparations have successfully controlled forest leaf-eating pests such as pine caterpillars and gypsy moths, effectively curbing pest outbreaks. In addition, Bt israelensis preparation is specially used to prevent and control mosquitoes and black fly larvae, and plays an important role in sanitary pest control. Some countries have used Bt suspension agent to treat water accumulation, which significantly reduces the density of mosquito-borne larvae (Figure 1) and reduces the risk of insect-borne disease transmission (Rudd et al., 2023). In terms of successful cases, after large-scale planting of cotton in China in the 1990s, the risk rate of cotton bollworms decreased significantly, and the amount of pesticides decreased by more than 70%, and the cotton bollworm population on cotton and surrounding crops was effectively suppressed (Kumar et al., 2019). 2.3 The status and problems of Bt in resistance management As an insecticidal microorganism, Bt is an active ingredient of a specific protein, which is more likely to trigger pests to develop resistance through a single mechanism than chemical pesticides. Therefore, while applying Bt on a large scale, resistance management has become an issue that must be paid attention to. Some pest populations have reported varying degrees of resistance to Bt toxins in laboratories and fields. For example, the resistance of diamondback moth to Bt kurstaki preparation was discovered as early as the 1990s, and since then, cases of resistance to Bt poison proteins such as bollworms and corn borers have also appeared one after another. The main mechanisms of pests' Bt resistance include mutations or decreased expression of midgut receptor genes that make it difficult to bind toxins, altered protease activity affects toxin activation, and enhanced removal of Bt bacteria in the insect immune system (Kumar et al., 2019). Resistant insects have significantly reduced sensitivity to Bt toxins and even exhibit interactive resistance to similar types of Cry proteins. 3 Cooperative Application with Natural Enemy Insects 3.1 The role and advantages of predatory insects (ladybugs, grass flies) Predatory natural enemy insects are an important factor in regulating pest populations in natural ecosystems. In farmland, predatory natural enemies such as ladybugs, squash, and hoverflies can prey on small pests such as aphids, whiteflies, and thrips in large quantities, reducing the pest base from the source (Patel and Purohit, 2014).
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