Microbes as Biocontrol Agents — Revision Notes

⚡ 30-Second Revision

Biocontrol: — Use of microbes to control pests/diseases.
***Bacillus thuringiensis* (Bt):** Bacterium, produces crystal proteins (delta-endotoxins). Targets lepidopteran (caterpillars), dipteran (mosquitoes), coleopteran (beetles) pests. Mechanism: Toxin activated in alkaline insect gut, creates pores, gut paralysis.
***Trichoderma* species:** Free-living fungus. Targets soil-borne fungal plant pathogens (*Pythium*, *Rhizoctonia*). Mechanisms: Mycoparasitism (lytic enzymes), competition, antibiosis, ISR.
Baculoviruses (e.g., NPV): — Viruses. Targets specific insect larvae (narrow-spectrum, mainly lepidopterans). Mechanism: Viral infection. Safe for non-target organisms, ideal for IPM.
Advantages: — Eco-friendly, specific, less resistance, safe for non-targets, used in organic farming.
Disadvantages: — Slower action, environmental sensitivity, shorter shelf life.

2-Minute Revision

Microbes as biocontrol agents offer an eco-friendly alternative to chemical pesticides for managing agricultural pests and diseases. The core idea is to use natural enemies to control harmful organisms.

Key examples include *Bacillus thuringiensis* (Bt), a bacterium that produces insecticidal crystal proteins (delta-endotoxins). These proteins are activated in the alkaline gut of specific insect larvae, like caterpillars, leading to their death.

Bt is widely used in sprays and genetically modified crops.

Another important agent is *Trichoderma* species, a free-living fungus found in the soil. *Trichoderma* is effective against various soil-borne fungal plant pathogens, such as *Pythium* and *Rhizoctonia*.

It works through mycoparasitism (attacking other fungi directly), competition for nutrients, and producing antifungal compounds. Lastly, Baculoviruses, particularly Nuclear Polyhedrosis Viruses (NPV), are highly host-specific viral insecticides.

They infect and kill specific insect larvae, primarily lepidopterans, without harming beneficial insects or other organisms, making them excellent for Integrated Pest Management (IPM). The main advantages of microbial biocontrol are their environmental safety, specificity, and reduced risk of pest resistance, though they may act slower and be sensitive to environmental conditions.

5-Minute Revision

Microbes as biocontrol agents represent a crucial shift towards sustainable agriculture, utilizing microorganisms to manage pests and plant diseases instead of harmful chemical pesticides. This approach leverages natural biological interactions, offering significant environmental and health benefits.

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***Bacillus thuringiensis* (Bt):** This is a soil-dwelling bacterium renowned for its insecticidal properties. During sporulation, Bt produces protein crystals (delta-endotoxins). When susceptible insect larvae, such as caterpillars (lepidopterans), mosquito larvae (dipterans), or certain beetles (coleopterans), ingest these crystals, the alkaline conditions in their midgut activate the protoxins. These active toxins bind to specific receptors on the gut cells, creating pores that disrupt the gut lining, leading to paralysis, septicaemia, and ultimately, the insect's death. Bt is highly specific due to the requirement for alkaline gut pH and specific receptors, making it safe for non-target organisms. It's used in sprays and genetically modified crops (e.g., Bt cotton).

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***Trichoderma* species:** These are free-living fungi commonly found in the rhizosphere (root zone). They are highly effective against a broad range of soil-borne fungal plant pathogens, including *Pythium*, *Rhizoctonia*, and *Sclerotium*. *Trichoderma* employs multiple mechanisms: mycoparasitism, where it directly attacks and parasitizes pathogenic fungi by coiling around their hyphae and secreting lytic enzymes (chitinases, glucanases) that degrade cell walls; competition for nutrients and space, outcompeting pathogens; antibiosis, producing antifungal compounds; and induced systemic resistance (ISR) in plants, enhancing their natural defenses. They also promote plant growth.

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Baculoviruses: — These are a group of viruses that are obligate parasites of insects and other arthropods. They are characterized by their extreme host specificity, meaning they infect and kill only a very narrow range of insect species, primarily lepidopteran larvae. Nuclear Polyhedrosis Viruses (NPV) are the most common type used in biocontrol. Their high specificity ensures that they do not harm beneficial insects (like pollinators or predators), birds, mammals, or plants. This makes them invaluable in Integrated Pest Management (IPM) programs, especially in ecologically sensitive areas, as they minimize ecological disruption.

Advantages of Microbial Biocontrol:

Environmental Safety: — Biodegradable, no harmful residues.
Specificity: — Target-specific, safe for non-target organisms.
Reduced Resistance: — Pests less likely to develop resistance.
Sustainability: — Promotes ecological balance, suitable for organic farming.

Disadvantages:

Slower Action: — May not be suitable for acute pest outbreaks.
Environmental Sensitivity: — Efficacy can be affected by temperature, humidity, UV light.
Storage: — Shorter shelf life, specific storage requirements.

Understanding these key microbes, their targets, mechanisms, and the overall benefits and limitations of biocontrol is essential for NEET.

Prelims Revision Notes

Microbes as biocontrol agents are living organisms used to control pests and diseases, offering an eco-friendly alternative to chemical pesticides. This topic is crucial for NEET, focusing on specific examples, their targets, and mechanisms.

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*Bacillus thuringiensis* (Bt):

* Type: Bacterium (Gram-positive, spore-forming). * Mechanism: Produces insecticidal crystal proteins (delta-endotoxins) during sporulation. * Action: When ingested by susceptible insect larvae (e.

g., caterpillars), alkaline gut pH activates protoxins. Active toxins bind to gut epithelial cells, creating pores, leading to gut paralysis and death. * Targets: Lepidopteran (caterpillars like corn borer, bollworm), Dipteran (mosquitoes), Coleopteran (beetles) pests.

* Application: Sprays, genetically modified crops (e.g., Bt cotton). * Specificity: High, due to specific gut pH and receptors.

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*Trichoderma* species:

* Type: Free-living fungus. * Habitat: Common in root ecosystems (rhizosphere). * Targets: Soil-borne fungal plant pathogens (e.g., *Pythium*, *Rhizoctonia*, *Sclerotium*). * Mechanisms: * Mycoparasitism: Directly attacks pathogenic fungi by coiling and secreting lytic enzymes (chitinases, glucanases).

* Competition: Outcompetes pathogens for nutrients and space. * Antibiosis: Produces antifungal compounds. * Induced Systemic Resistance (ISR): Enhances plant's natural defenses. * Application: Seed treatments, soil amendments.

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Baculoviruses (e.g., Nuclear Polyhedrosis Virus - NPV):

* Type: Viruses. * Targets: Highly host-specific insect larvae, primarily lepidopteran pests. * Mechanism: Viral infection, replication within host cells, leading to death. * Specificity: Narrow-spectrum, do not harm non-target organisms (beneficial insects, birds, mammals, plants). * Importance: Excellent for Integrated Pest Management (IPM) due to safety and specificity.

General Advantages of Microbial Biocontrol:

Environmentally safe, biodegradable, no harmful residues.
Highly specific, minimizes harm to non-target organisms.
Reduced risk of pest resistance development.
Sustainable, suitable for organic farming.

General Disadvantages:

Slower action compared to chemical pesticides.
Efficacy sensitive to environmental factors (temperature, humidity, UV).
Shorter shelf life, specific storage requirements.

Vyyuha Quick Recall

Be Throughful, Treat Roots, Be Very Specific!

Be Throughful: Bacillus Thuringiensis (Bt) - targets insect larvae.
Treat Roots: Trichoderma - targets Root-borne fungal pathogens.
Be Very Specific: Baculoviruses - Viral, highly Specific to insect pests.