🐞Biological Control — Parasitoids, Predators, and Microbial Agents

Nature’s Own Pest Control

The previous lesson covered cultural, physical, and mechanical control — methods that modify the environment or physically remove pests. This lesson introduces the fourth IPM component: biological control, which harnesses living organisms to suppress pest populations.

In 1888, California’s citrus industry was being destroyed by the cottony cushion scale — an invasive pest from Australia. Instead of chemicals, scientists introduced the Vedalia beetle (Rodolia cardinalis), a natural predator from Australia. Within two years, the scale was under complete control. This landmark success proved that nature’s own enemies can be more effective than any chemical — and it launched the modern science of biological control.

Indian agriculture uses biological control extensively today. Trichogramma parasitoid wasps are released on millions of hectares of sugarcane and rice. Chrysoperla lacewings protect cotton from aphids. Understanding these natural enemies — who eats whom, who parasitises whom — is essential for both farming practice and competitive exams.

This lesson covers:

1. Parasitoids — crop-pest-parasitoid associations (the most-tested table)
2. Predators — ladybird beetles, lacewings, Cryptolaemus
3. Microbial agents — Bt, NPV, Beauveria, Metarhizium
4. Insect collecting traps and cocoon types

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What Is Biological Control?

Biological control is the use of natural enemies — parasitoids, predators, and pathogens — to suppress pest populations below the Economic Injury Level (EIL).

Three categories of natural enemies are used:

1. Parasitoids — insects whose larvae develop inside or on a single host, killing it
2. Predators — organisms that kill and consume multiple prey during their lifetime
3. Microbial agents — bacteria, viruses, and fungi that cause disease in insects

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1. Parasitoids

A parasitoid is an insect whose immature stage develops on or within a single host insect, eventually killing it. The adult parasitoid is free-living and does not feed on the host.

Key difference from parasites: A parasite weakens but does not kill its host. A parasitoid always kills its host.

Important Parasitoids in Indian Agriculture

Parasitoid Classification by Stage Attacked

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2. Predators

Predators kill and consume multiple prey during their lifetime. Unlike parasitoids, they are usually larger than their prey and do not develop inside the host.

Important Predators in Indian Agriculture

Parasitoids vs Predators — A Comparison

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3. Microbial Biocontrol Agents

Microbial agents are bacteria, viruses, and fungi that cause disease in pest insects. They offer the advantage of being highly specific — they kill the target pest without harming beneficial insects or humans.

Stomach vs Contact Mode of Action in Bioagents

NPV and Silkworm Disease

• NPV causes Grasserie disease (jaundice) of silkworm (Bombyx mori)
• Infected larvae become swollen, yellowish, and their body contents liquefy
• Larvae hang inverted from branches/rearing trays in the characteristic symptom called Caterpillar wilt

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Insect Collecting Traps and Equipment

Field monitoring requires the right trap for the right insect. This table links specific pests to their recommended collection method.

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Types of Cocoons

Different insect orders and species construct different cocoon types during pupation. This classification is a niche but regularly tested topic.

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When to Use Which Biocontrol Agent?

Quick decision guide for field officers:

Critical timing rule: Biocontrol agents must be released before pest population explodes. Once pest is at epidemic level, biocontrol alone cannot save the crop — you’ll need to integrate with other methods.

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Exam Tips and Mnemonics

1. Vedalia beetle story — the first major biological control success (1888, California, cottony cushion scale). Know the pest, predator, and country.
2. Trichogramma = egg parasitoid. If the question says “egg parasitoid,” think Trichogramma first.
3. Cryptolaemus = mealy bug predator. The name sounds like “crypto-lame-us” — mealy bugs are cryptic (hidden) and lame (slow-moving).
4. NPV is virus, Bt is bacterium, Beauveria is fungus — know the type of each microbial agent.
5. Puparium belongs to Diptera. All other cocoon types belong to Lepidoptera or Coleoptera.

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Summary Table

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Summary Cheat Sheet