What is biocontrol? Explain the use of any three microbes as biocontrol agents and state its advantages.

1. 1 · Define biocontrol. Biocontrol is the use of biological methods to control plant diseases and pests instead of toxic chemicals.
2. 2 · Bacillus thuringiensis. Dried spores sprayed on plants; caterpillars eat them; toxin released in the larval gut kills them; Bt genes in Bt cotton.
3. 3 · Trichoderma. Free-living fungus of root ecosystems; controls several plant pathogens.
4. 4 · Baculoviruses. Genus Nucleopolyhedrovirus; species-specific, narrow-spectrum; no harm to non-target organisms; useful in IPM.
5. 5 · Advantages.
   • No toxic residues; less pollution of soil, water and food.
   • Useful organisms and biodiversity are conserved.
   • Less dependence on chemical pesticides.
6. 6 · Link to daily life. Fewer pesticide residues on vegetables and fruits.
7. 7 · Close in one line. So biocontrol keeps pests in check while protecting health and the environment.

Scoring tip: Name the genus Nucleopolyhedrovirus and say where the Bt toxin acts. These two details separate a full-mark answer from an average one.