Invisible attacks, destructive curses…How many unique skills do the “vanguards” of microbial pesticides have?

Produced by: Science Popularization China

Author: Liu Liqiong (Institute of Microbiology, Chinese Academy of Sciences)

Producer: China Science Expo

In the long history of agricultural production, pests and diseases have always been a problem that has troubled farmers and scientists. From the ancient physical and chemical control to the booming biological control today, people have been exploring ways to prevent and control pests and diseases, and microbial pesticides are becoming a shining star in the field of biological control. With their unique mode of action, ecological and environmental characteristics, and broad application prospects, they are gradually becoming an important support for the sustainable development of modern agriculture.

What is microbial pesticide? What secrets does it hold?

Microbial pesticides, in simple terms, are a type of pesticide that uses microorganisms or their metabolites to "attack" diseases, insects, weeds, and rodents that harm crops, while also helping crops thrive. It is completely different from the "fighting method" of traditional chemical pesticides. The "soldiers" here can be living microorganisms, such as bacteria, fungi, viruses, etc. They parasitize, compete, or release toxins, cleverly suppressing or eliminating those troublesome pests and diseases, and protecting the harmony and stability of the agricultural ecosystem.

Who are the pioneers in the microbial pesticide camp?

According to the types of microorganisms contained and their uses, microbial pesticides can be divided into microbial insecticides (bacterial insecticides, fungal insecticides, viral insecticides), microbial fungicides (such as Bacillus subtilis), microbial herbicides, rodenticides, agricultural antibiotics, etc. Let's invite a few star fighters on the microbial insecticide front to see the style of microbial pesticides in defeating and killing enemies.

Fungal insecticides: the "invisible attack" of Beauveria bassiana and Metarhizium anisopliae

Beauveria bassiana and Metarhizium anisopliae, these two fungi are like assassins hiding in the dark, and their spores are tiny "hidden weapons" that quietly lurk in the environment. Once pests come into contact with them, under suitable temperature and humidity, the spores immediately germinate and grow, and the hyphae, like flexible silk threads, quickly break through the pest's body wall defenses and spread inside the pest, absorbing nutrients from the pest's body while releasing deadly toxins to disrupt the pest's physiological functions, causing the pest to gradually become rigid. This unique attack method allows them to launch a fatal attack on pests that are good at hiding.

Caterpillars eating cabbage

(Photo source: veer photo gallery)

Bacterial insecticides: Bacillus thuringiensis (Bt)'s "precision attack"

Bacillus thuringiensis (Bt) is a legend in the bacterial world. When its spores are formed, a unique paraspore crystal protein is woven. When pests eat plants containing Bt, this protein will be instantly activated in the alkaline environment of the pest's intestines. Then, like an arrow with precise navigation, it quickly locks onto the specific receptors on the surface of the intestinal epithelial cells, and then deeply penetrates the cell membrane, opening up countless tiny channels. This process breaks the balance chain in the pest's body, paralyzing its intestines, stopping its feeding function, and ultimately leading to the defeat of the pest.

Viral insecticides: the "destructive curse" of nuclear polyhedrosis virus (NPV) and granulovirus (GV)

Nuclear polyhedrosis virus (NPV) and granulovirus (GV) are "messengers of destruction" specifically targeting lepidopteran pests. When pests eat plants containing these viruses, it is like being imposed with an inescapable "curse of destruction". The virus replicates violently in the pest's body, wantonly disintegrating the pest's cells and tissues. The infected pests gradually become slow in movement, lose their appetite, and eventually die. The dead body of the pest is like a "treasure trove of viruses". The viruses released after the rupture continue to look for new targets, forming a continuous transmission chain.

What are the significant advantages of microbial pesticides compared to traditional pesticides?

**First of all, microbial pesticides are very friendly to the environment. **Chemical pesticides will leave long-lasting "scars" in the soil and water, but microbial pesticides will quickly decompose after completing their mission, "without taking a cloud." Take Bacillus thuringiensis as an example. After completing its insecticide mission, the spores and crystal proteins will be integrated into the natural cycle and decomposed silently, without causing any damage to the soil structure and microbial community. They will not harm "innocent" non-target organisms such as birds, fish, beneficial insects, etc.

**Secondly, in sharp contrast to the single mode of action of chemical pesticides, microbial pesticides have a complex and sophisticated mechanism of action in combating pest resistance and can always maintain a stable and efficient prevention and control effect,** becoming a powerful weapon to address the problem of pest resistance.

Because the targets of microbial pesticides are precisely locked on the unique physiological structure and metabolic pathways of pests, and the physiological systems of pests are very different from those of humans and mammals. For humans and mammals, they are like facing a solid invisible shield. Therefore, under normal use, people do not need to worry about safety issues.

In fact, microbial pesticides utilize the biodiversity in nature to protect agricultural production in an eco-friendly way.

Experimental samples

(Photo source: Gansu Academy of Sciences)

Where do microbial pesticides come from and where do they go?

Like "treasure hunters", researchers have painstakingly searched for potential microbial strains in nature. After finding them, they use advanced technology to domesticate and improve the strains, making them superior in terms of stress resistance and pathogenicity to pathogens. In the fermentation process, the temperature, pH value and other conditions are precisely controlled to create an excellent environment for the growth and reproduction of microorganisms. Finally, through clever formula design and dosage form selection, it is made into various forms such as powder and aqueous solution to meet the needs of different scenarios.

Microbial pesticides have a wide range of applications. In the vast farmland, whether it is food crops such as wheat and rice, cash crops such as cotton and peanuts, or vegetables, fruit trees, tea trees, etc., they are also a powerful helper in forestry protection, horticulture and flower industry, and urban greening.

Of course, microbial pesticides are not perfect. Their efficacy is easily restricted by environmental factors. If the temperature, humidity and light are not appropriate, the control effect will be greatly reduced. For example, high temperature may reduce the activity of microorganisms. Compared with chemical pesticides, microbial pesticides often take several days or even longer to be effective, making it difficult to deal with sudden pests and diseases.

With the in-depth application of modern biotechnologies such as genetic engineering, microbial pesticides are expected to acquire stronger performance and better environmental adaptability, playing a more critical role in achieving harmonious coexistence of agriculture and ecology and ensuring food security.