Biological Control of Pests — Revision Notes

⚡ 30-Second Revision

Biological Control: — Using natural enemies (predators, parasitoids, pathogens) to manage pests.
Predators: — Ladybug $\rightarrow$ Aphids; Dragonfly $\rightarrow$ Mosquitoes.
Parasitoids: — *Trichogramma* wasps $\rightarrow$ Moth eggs (e.g., sugarcane borers).
Pathogens:

- *Bacillus thuringiensis* (Bt) $\rightarrow$ Lepidopteran larvae (e.g., cotton bollworm, corn borer). Mechanism: Bt toxin crystals activated in alkaline gut, form pores, kill insect. - *Trichoderma* spp. (fungus) $\rightarrow$ Root-borne plant pathogens (e.g., *Pythium*, *Rhizoctonia*). Mechanism: Mycoparasitism, antibiosis, competition, ISR. - Baculoviruses (NPV) $\rightarrow$ Species-specific insect larvae. Mechanism: Narrow host specificity, no harm to non-targets.

Advantages: — Eco-friendly, no pollution, no resistance, preserves biodiversity, part of IPM.

2-Minute Revision

Biological control is an environmentally friendly method of pest management that employs living organisms, known as natural enemies, to keep pest populations in check. These natural enemies fall into three categories: predators, parasitoids, and pathogens.

Predators, like ladybugs, consume multiple prey (e.g., aphids), while dragonflies prey on mosquitoes. Parasitoids, such as *Trichogramma* wasps, lay eggs inside pest eggs, eventually killing the host.

Pathogens include microbes like *Bacillus thuringiensis* (Bt), a bacterium whose toxins target lepidopteran larvae (caterpillars) by disrupting their gut. *Trichoderma* species are fungi that protect plant roots from diseases caused by other fungi.

Baculoviruses, specifically Nucleopolyhedrovirus (NPV), are highly specific viral pathogens of insects, posing no threat to non-target organisms. This approach is a cornerstone of Integrated Pest Management (IPM), aiming for sustainable agriculture by reducing reliance on chemical pesticides, minimizing pollution, and preventing the development of pest resistance.

5-Minute Revision

Biological control represents a crucial shift towards sustainable pest management, moving away from harmful chemical pesticides. It harnesses nature's own mechanisms by introducing or encouraging natural enemies of pests. These enemies are categorized as predators, parasitoids, and pathogens.

Predators are organisms that actively hunt and consume multiple prey. Classic examples include ladybugs (Coccinellids) which are highly effective against aphids and other soft-bodied insects, and dragonflies which are excellent at controlling mosquito populations.

Parasitoids are insects, often wasps or flies, that lay their eggs in or on a single host insect. The developing parasitoid larva then feeds on and eventually kills the host. _Trichogramma_ wasps are widely used parasitoids that target the eggs of various lepidopteran pests, such as sugarcane borers and cotton bollworms, preventing the larvae from hatching.

Pathogens are microorganisms that cause disease in pests. Key examples for NEET include:

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***Bacillus thuringiensis* (Bt): A bacterium that produces insecticidal protein crystals. When ingested by susceptible insect larvae (primarily lepidopterans** like cotton bollworms), the alkaline conditions in their gut activate the protoxins, which then bind to gut cells, creating pores and leading to gut paralysis and death. Bt is highly specific and safe for non-target organisms.
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***Trichoderma* species: These are free-living fungi found in root ecosystems. They act as bio-fungicides against various root-borne plant pathogens** (e.g., *Pythium*, *Rhizoctonia*). Their mechanisms include mycoparasitism (attacking other fungi), antibiosis (producing inhibitory compounds), competition for resources, and inducing systemic resistance in plants.
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**Baculoviruses (specifically *Nucleopolyhedrovirus* - NPV): These are viruses that infect insects and other arthropods. They are prized for their narrow host specificity**, meaning they target only specific insect species, making them extremely safe for beneficial insects, plants, mammals, and humans. They are excellent for species-specific insecticidal applications in ecologically sensitive areas.

Biological control is a core component of Integrated Pest Management (IPM), a holistic strategy that combines various methods for long-term pest prevention. Its advantages over chemical control are significant: it's eco-friendly, non-polluting, reduces the risk of pest resistance, and helps preserve biodiversity. Understanding these specific examples, their mechanisms, and the overarching benefits is crucial for NEET.

Prelims Revision Notes

Biological Control of Pests: NEET Revision Notes

1. Definition & Principle:

Utilizes natural enemies (predators, parasitoids, pathogens) to control pest populations.
Goal: Reduce pest numbers to economically tolerable levels, not complete eradication.
Eco-friendly alternative to chemical pesticides.
Key component of Integrated Pest Management (IPM).

2. Types of Natural Enemies & Examples:

Predators: — Organisms that hunt and consume multiple prey.

* Ladybugs (Coccinellids): Prey on aphids and other soft-bodied insects. * Dragonflies: Prey on mosquitoes and other flying insects.

Parasitoids: — Insects that lay eggs in/on a single host, eventually killing it.

* ***Trichogramma* wasps: Parasitize eggs of lepidopteran pests** (e.g., sugarcane borers, cotton bollworms).

Pathogens (Microbial Biocontrol Agents): — Microorganisms causing disease in pests.

* ***Bacillus thuringiensis* (Bt):** * Bacterium producing insecticidal protein crystals (Cry proteins). * Target: Larvae of Lepidoptera (moths/butterflies, e.g., cotton bollworm, corn borer), some Diptera, Coleoptera.

* Mechanism: Crystals ingested $\rightarrow$ solubilized in alkaline gut $\rightarrow$ protoxins activated by proteases $\rightarrow$ bind to midgut receptors $\rightarrow$ form pores $\rightarrow$ cell lysis, gut paralysis $\rightarrow$ death.

* Specificity: Requires alkaline gut and specific receptors, making it harmless to non-target organisms. * Application: Bio-pesticide sprays, Bt-crops (e.g., Bt cotton). * ***Trichoderma* species:** * Free-living fungi common in root ecosystems.

* Target: Various root-borne plant pathogens (e.g., *Pythium*, *Phytophthora*, *Rhizoctonia*). * Mechanism: Mycoparasitism (attacking other fungi), antibiosis (producing inhibitory compounds), competition for nutrients/space, Induced Systemic Resistance (ISR) in plants.

* Application: Seed treatment, soil amendment (bio-fungicide). * **Baculoviruses (Genus *Nucleopolyhedrovirus* - NPV):** * Viruses that infect insects and other arthropods. * Target: Species-specific insect larvae.

* Key Feature: Narrow host specificity (do not harm non-target insects, plants, mammals, birds, fish). * Application: Excellent for IPM, especially in ecologically sensitive areas.

3. Advantages of Biological Control:

Environmentally friendly (no pollution).
Highly specific (targets only pests, spares beneficial organisms).
No development of pest resistance (due to complex interactions).
Sustainable and long-term solution.
Preserves biodiversity.
Safe for humans, livestock, and wildlife.

4. Integrated Pest Management (IPM):

Holistic approach combining various methods (biological, cultural, physical, chemical).
Aims for long-term pest prevention and management, minimizing chemical use.
Biological control is a cornerstone of IPM.

Vyyuha Quick Recall

To remember key biocontrol agents and their targets:

Ladybugs Always Devour Aphids. Dragonflies Munch Mosquitoes. Bt Controls Caterpillars (Lepidopterans). Trichoderma Roots Rot (Root-borne pathogens). Baculoviruses Specifically Infect Insects (Species-specific insect larvae).

Mnemonic: LADA (Ladybug-Aphid) DMM (Dragonfly-Mosquito) BCC (Bt-Caterpillar) TRR (Trichoderma-Root Rot) BSII (Baculovirus-Specific Insect).