8 min readConcept sheet1-mark MCQ or assertion-reason on Bt, Trichoderma or baculoviruses, a 2 or 3-mark question on biocontrol and its advantages; also a NEET favourite

Microbes as biocontrol agents

Biocontrol uses living things, not toxic chemicals, to keep pests and plant diseases in check: ladybirds, dragonflies, Bacillus thuringiensis, Trichoderma and baculoviruses.

BiocontrolUse of biological methods to control plant diseases and pests

Bacillus thuringiensis (Bt)Bacterium whose toxin kills butterfly caterpillars but leaves other insects unharmed

TrichodermaFree-living fungus of root ecosystems; controls several plant pathogens

BaculovirusesInsect pathogens, mostly genus Nucleopolyhedrovirus; species-specific and narrow-spectrum

Chemical control vs biological control

Conventional (chemical) farmingUses insecticides, pesticides and weedicides that kill useful and harmful life forms indiscriminately. They are toxic to humans and animals and pollute soil, groundwater, fruits and vegetables.

Organic farming with biocontrolBelieves that biodiversity furthers health. Pests are not wiped out but kept at manageable levels by natural predators and parasites. The farmer studies the pests, their predators, life cycles, feeding and habitats to choose the right biocontrol.

Wiping out pests completely is not desirable: the useful predatory and parasitic insects that feed on them would then die out too.

Biocontrol agents to know

Agent	Type	Controls
Ladybird (red and black beetle)	Insect predator	Aphids
Dragonflies	Insect predator	Mosquitoes
Bacillus thuringiensis (Bt)	Bacterium	Butterfly caterpillars
Trichoderma	Free-living fungus in root ecosystems	Several plant pathogens (plant diseases)
Baculoviruses (genus Nucleopolyhedrovirus)	Viruses that attack insects and other arthropods	Specific insect pests; species-specific, narrow-spectrum

How Bt kills caterpillars

1
Dried spores of Bt are sold in sachets, mixed with water and sprayed on plants such as brassicas (cabbage, cauliflower) and fruit trees.
2
Caterpillars (insect larvae) eat the sprayed leaves.
3★
In the gut of the larva, the toxin is released and the larva is killed.
4
Other insects are left unharmed.
5
Using genetic engineering, scientists put Bt toxin genes into plants, making them resistant to insect pests; Bt cotton is grown in some states of India.

★ key step

Baculoviruses and integrated pest management

Most baculoviruses used in biocontrol belong to the genus Nucleopolyhedrovirus. They attack only certain insects, so they are species-specific and narrow-spectrum. They have no negative effect on plants, mammals, birds, fish or non-target insects. This makes them ideal for an integrated pest management (IPM) programme, where useful insects are protected, and for ecologically sensitive areas.

In real life

Fewer chemical sprays mean fewer pesticide residues on the vegetables and fruits we eat. Many Indian farmers now use Trichoderma-treated seeds and Bt sprays as part of organic and integrated pest management.

Exam angle

2 marks: “How does Bacillus thuringiensis act as a biocontrol agent?” Dried Bt spores are sprayed on plants; caterpillars eat them; the toxin is released in the larval gut and kills the larvae, leaving other insects unharmed.

3 marks: “Why are baculoviruses considered good biocontrol agents? Name the genus mostly used.” Species-specific, narrow-spectrum insecticides; no harm to plants, mammals, birds, fish or non-target insects; suitable for IPM and sensitive areas. Genus Nucleopolyhedrovirus.

3 marks: “Name one biocontrol agent each against aphids, mosquitoes and plant pathogens. Give two advantages of biocontrol over chemical pesticides.” Ladybird (aphids), dragonflies (mosquitoes), Trichoderma (plant pathogens). Advantages: no toxic residues or pollution; useful organisms spared; less dependence on chemicals.

Remember it

Ladybird eats aphids, Dragonfly eats mosquitoes, Bt kills caterpillars, Trichoderma fights plant disease, Baculovirus targets one pest.