Question
What are biocontrol agents? Explain how Trichoderma, Baculovirus (NPV), and ladybugs are used as biological pest control agents. Why is biocontrol preferred over chemical pesticides?
(NCERT Class 12 — asked in NEET and CBSE boards)
Solution — Step by Step
Biological control (biocontrol) uses living organisms or their products to control pests, instead of synthetic chemical pesticides. The idea is to use natural enemies — predators, parasites, or pathogens — to keep pest populations in check.
This is part of Integrated Pest Management (IPM), which combines biological, cultural, and minimal chemical methods.
Trichoderma is a free-living fungus found in soil that acts against several plant pathogens.
How it works:
- Mycoparasitism — Trichoderma hyphae coil around and penetrate the pathogenic fungus, killing it
- Produces antibiotics and cell wall-degrading enzymes that destroy pathogen cells
- Competes with pathogens for space and nutrients
Used against soil-borne diseases caused by Fusarium, Rhizoctonia, and Pythium. Available commercially as bio-fungicide formulations.
Nucleopolyhedrovirus (NPV) is a type of baculovirus that specifically infects and kills insects.
Advantages:
- Highly specific — each NPV strain attacks only one or a few insect species, leaving non-target organisms (including beneficial insects, birds, and humans) unharmed
- No environmental pollution
- Does not affect plants or other animals in the ecosystem
The virus is applied to crops; when the target insect eats treated leaves, the virus replicates inside its body and kills it.
Ladybird beetles are voracious predators of aphids, which are among the most destructive crop pests.
A single ladybug can eat up to 50-60 aphids per day. They also feed on scale insects, mealybugs, and mites.
Other predatory biocontrol agents: dragonflies (eat mosquitoes), Gambusia fish (eat mosquito larvae).
Why This Works
Biocontrol works because it leverages natural predator-prey relationships that have evolved over millions of years. Unlike chemical pesticides, biocontrol agents:
- Don’t leave toxic residues in soil or water
- Don’t harm non-target organisms (pollinators like bees are safe)
- Don’t lead to pesticide resistance (a growing problem with chemicals)
- Are self-sustaining — once predator populations establish, they keep controlling pests
Chemical pesticides kill indiscriminately — they destroy pests AND beneficial organisms (bees, earthworms, natural predators). This often leads to pest resurgence because the natural enemies are wiped out too.
Alternative Method — Biocontrol Examples Summary
For NEET, keep this quick reference:
| Agent | Type | Controls |
|---|---|---|
| Trichoderma | Fungus | Soil-borne plant pathogens |
| Baculovirus (NPV) | Virus | Specific insect pests |
| Ladybird beetle | Insect predator | Aphids |
| Bacillus thuringiensis (Bt) | Bacterium | Insect larvae (produces Bt toxin) |
| Gambusia fish | Fish predator | Mosquito larvae |
Bt toxin is also the basis of Bt cotton and Bt brinjal — transgenic crops that produce their own insecticide. Don’t confuse the biocontrol organism with the transgenic crop.
Common Mistake
Students often confuse biofertilisers with biocontrol agents. Biofertilisers (Rhizobium, mycorrhiza, cyanobacteria) enhance soil fertility. Biocontrol agents (Trichoderma, NPV, ladybugs) control pests. They serve completely different purposes. If NEET asks “Which is used in biocontrol?”, Trichoderma and NPV are correct — not Rhizobium (that’s a biofertiliser).