Potential Applications of Bacillus thuringiensis in Agriculture

Bacillus thuringiensis (Bt) is a Gram-positive bacterium widely found in soil and plant microenvironments. Since its discovery in the early 20th century, it has become one of the most influential microorganisms in global agriculture. Its application in agriculture centers on the insecticidal crystal proteins (ICPs) it produces, primarily δ-endotoxins (such as Cry proteins and Cyt proteins), as well as vegetative insecticidal proteins (VIPs) secreted during the vegetative phase. These proteins exhibit highly specific stomach toxicity against the larvae of certain insects (especially Lepidoptera, Coleoptera, Diptera, and some nematodes), while being safe for humans, vertebrates, beneficial insects, and most non-target organisms. This characteristic makes it an ideal alternative to chemical insecticides, playing a crucial role in promoting green and sustainable agricultural development. Its potential applications are mainly reflected in the following aspects and continue to develop in depth.

As a Microbial Biopesticide: A Classic and Widespread Application

This is the most traditional and mature application of Bt. Bt strains are cultured through industrial fermentation, and their spores and crystal proteins are collected and processed into wettable powders, suspension concentrates, granules, or water-dispersible granules. After application, pests ingest plant tissues containing the toxins. The toxins are dissolved and activated in the alkaline environment of their intestines, binding to specific receptors on the midgut epithelial cells, causing cell membrane perforation, ultimately leading to the cessation of feeding, paralysis, and death of the pests.

Its advantages are significant:

1.High target specificity: Different Bacillus thuringiensis strains or subspecies produce toxins with different insecticidal spectra. For example, Bacillus thuringiensis kurstaki is effective against lepidopteran larvae, while Bacillus thuringiensis israelensis specifically targets dipteran larvae such as mosquitoes and flies. This specificity protects pollinating insects (such as bees), natural enemy insects (such as ladybugs and parasitic wasps), and beneficial soil organisms, maintaining the ecological balance of farmland.

2.Environmentally friendly: Bacillus thuringiensis proteins are rapidly degraded by sunlight and microorganisms in the natural environment, posing no residue risk and not polluting groundwater and soil. Its application does not disrupt the long-term stability of the ecosystem.

3.Resistance Management Tool: In integrated pest management (IPM) systems, using Bt formulations in rotation or combination with chemical pesticides can effectively delay the development of resistance in pests to single-mechanism pesticides.

4.Suitable for Sensitive Scenarios: Bacillus thuringiensis formulations are indispensable and compliant inputs in organic farming, green food production bases, urban landscaping, and mosquito control in water source areas.

As a Gene Source for Genetically Modified Insect-Resistant Crops: A Revolutionary Industrial Application

Since the 1990s, plant genetic engineering technology has been used to transfer genes encoding Bacillus thuringiensis toxin proteins into major crops, allowing for continuous, localized expression within the plant, thereby conferring insect resistance to the crops themselves. This represents a revolutionary leap in Bacillus thuringiensisapplication.

1.Major Achievements: Bacillus thuringiensis cotton, Bacillus thuringiensis corn, and Bacillus thuringiensis soybeans have been commercially cultivated on a large scale in dozens of countries worldwide. In China, for example, the promotion of Bacillus thuringiensis cotton has fundamentally controlled the cotton bollworm, significantly reducing pesticide use and effectively protecting farmers’ income and the health of the agricultural environment.

2.Core Advantages:

• All-Weather Protection: The plant is protected throughout its entire growth cycle (or in specific tissues), especially effective against boring and concealed pests (such as the European corn borer), which is difficult to achieve with sprayed pesticides.

• Reduced Labor and Costs: Reduces farmers’ exposure to pesticides and labor intensity.

• Improved Ecosystem Services: Reduced field spraying significantly increases agricultural biodiversity.

3.Challenges and Responses:

Risk of Resistance Evolution: Long-term, single-toxin selection pressure may lead to the development of resistance in pests. Strategies to address this include implementing a “high-dose/refuge” strategy (requiring the planting of a certain proportion of non-Bacillus thuringiensis host plants to maintain a susceptible pest population), developing “gene stacking” or “gene pyramiding” crops (simultaneously expressing two or more Bacillus thuringiensis toxins with different mechanisms of action), and conducting rigorous field resistance monitoring. III. As a Core Component of Integrated Pest Management (IPM): Systemic and Integrated Application

Modern agriculture emphasizes IPM, and Bacillus thuringiensis can be integrated at multiple levels

Synergy with biological control:  

1.Combined use with natural enemies of insects (parasitic wasps, predatory mites), entomopathogenic nematodes, or insect viruses (such as nuclear polyhedrosis virus) often produces synergistic effects without mutual interference.

2.Combination with agricultural practices:  Used in conjunction with agronomic measures such as crop rotation, insect-resistant varieties, and trap crops, forming a multi-dimensional pest suppression system.

3.Compatibility with low-risk chemical pesticides: During pest outbreaks, mixed use with specific insect growth regulators or low-toxicity chemical pesticides can quickly reduce pest populations while reducing the use of highly toxic pesticides.

Discovery of New Functions and Technological Innovation: A Blue Ocean for Future Applications

With the advancement of biotechnology, the application potential of Bacillus thuringiensis is constantly expanding:

1.Discovery and modification of new insecticidal proteins: Continuously discovering new toxin genes from wild strains that are effective against new pests (such as thrips and aphids) or pests that have developed resistance. Modifying existing toxins through protein engineering techniques to enhance their activity, broaden their insecticidal spectrum, or overcome existing resistance.

2.Development of multifunctional strains: SomeBacillus thuringiensis strains can not only kill insects but also produce antibacterial substances to inhibit plant pathogens (such as Fusarium and Rhizoctonia), or secrete plant growth-promoting substances, possessing the multiple potential of “insect control + disease prevention + growth promotion.”

3.Intelligent delivery systems: Utilizing seed treatment technology, using Bacillus thuringiensis as a seed coating agent; or developing bionanomaterials to encapsulate Bacillus thuringiensis toxins to improve their stability and rainfastness in the field; and even exploring the use of plant endophytes or rhizosphere growth-promoting bacteria as carriers to introduce and express Bacillus thuringiensis toxin genes in plants.

4.Addressing non-lepidopteran pests: Actively screening and verifying effective Bacillus thuringiensis strains and toxins against increasingly serious coleopteran (such as potato beetles and root maggots) and hemipteran (such as planthoppers and stink bugs) pests to expand their control range.

5.Deepening the Role of Bacillus thuringiensis in Sustainable Agricultural Systems: Within the framework of ecological and regenerative agriculture, Bacillus thuringiensis, as a biological input, combined with conservation tillage practices such as cover cropping and no-till or reduced tillage, contributes to building more resilient agricultural production systems.

Conclusion and Outlook

The application of Bacillus thuringiensis(Bt) in agriculture has evolved from simple direct spray formulations to genetically modified crops, key components of integrated pest management (IPM), and even cutting-edge explorations of multifunctional biological agents. Its core value lies in providing an efficient, safe, and environmentally compatible pest management solution. In the future, its development will focus more on precision (targeting specific pests and crops), sustainability (mitigating resistance and protecting the environment), and integration (combining with other green technologies). Despite challenges such as the evolution of pest resistance and public perception differences regarding genetically modified technologies, with the deepening of scientific research, the improvement of regulatory policies, and the popularization of public education, Bacillus thuringiensis will undoubtedly continue to play an irreplaceable role in ensuring global food security, reducing agricultural non-point source pollution, and promoting the transformation of agriculture towards green and sustainable development. The full realization of its potential depends on interdisciplinary collaborative innovation across microbiology, molecular biology, ecology, agronomy, and policy science.