Biocontrol Agents and Biofertilisers: Quick Revision

A brief note on Biocontrol Agents and Biofertilisers. Read it before a test. Try each question at the end before you open its answer.

Biocontrol

• Chemical pesticides: toxic to people and animals, and they pollute the soil and the water.
• Ladybird: aphids. Dragonfly: mosquitoes.
• Bacillus thuringiensis (Bt): dried spores in sachets, mixed with water and sprayed. The larva eats them, the toxin is released in its gut and it dies.
• Trichoderma: a free-living fungus, a biocontrol agent of plant pathogens.
• Baculoviruses (genus Nucleopolyhedrovirus): attack insects and arthropods. They are species specific and narrow spectrum, so they are useful in integrated pest management.

Biofertilisers

• Rhizobium: symbiotic with the roots of legumes, in root nodules, fixes nitrogen.
• Azospirillum and Azotobacter: free-living bacteria that enrich the nitrogen of the soil.
• Mycorrhiza (Glomus): a fungus on roots. It passes phosphorus to the plant. The plant resists root pathogens and tolerates salinity and drought.
• Cyanobacteria (Anabaena, Nostoc, Oscillatoria): autotrophic nitrogen fixers, important in paddy fields.

A worked example

A field of 4 hectares has a biofertiliser that supplies 25 kg of nitrogen to each hectare. Urea is 46 per cent nitrogen. How much urea is saved?

1. The nitrogen is $4 \times 25 = 100$ kg.
2. The urea is $100 / 0.46 = 217.4$ kg.

Practice with new numbers

A program to try

The program prints the larvae on a plant for each of three days after a spray.

Mistakes to avoid

• Mixing up the spray and Bt cotton. The spray is the bacterium. The cotton is a plant with the gene.
• **Saying that Azotobacter lives in nodules.** It is free-living.
• Saying that mycorrhiza fix nitrogen. They bring phosphorus.
• Calling cyanobacteria heterotrophic. They are autotrophic.

Check yourself

1. Which pest does the ladybird control?

2. What is the group of Glomus, and what does it give to a plant?

3. Which microbe fixes nitrogen in the root nodules of legumes?

4. Why are baculoviruses useful in integrated pest management?

Sources

• NCERT (2023). Biology, Textbook for Class XII, chapter 8, Microbes in Human Welfare.
• Smith S. E. and Read D. J. (2008). Mycorrhizal Symbiosis, 3rd edition, Academic Press.