Biofertilisers and Biocontrol Agents
Biofertilisers and biocontrol agents let farmers cut down chemical fertilisers and pesticides by using living organisms instead. This page explains biocontrol and the organic farmer's approach, ladybirds and dragonflies, Bacillus thuringiensis, Trichoderma and baculoviruses, and then the biofertilisers: Rhizobium, free-living nitrogen fixers, mycorrhiza and cyanobacteria, as in the NCERT Class 12 chapter Microbes in Human Welfare. NEET often pairs each organism with its target or nutrient, so learn every pair of biofertilisers and biocontrol agents exactly.
- ★ Must learn Biocontrol: the use of biological methods to control plant diseases and pests.
- Chemical insecticides and pesticides are toxic and pollute soil, ground water, fruits, vegetables and crops; weedicides pollute soil.
- The organic farmer keeps pests at manageable levels through checks and balances, and does not eradicate them.
- The ladybird controls aphids; dragonflies control mosquitoes.
- ★ Must learn Bacillus thuringiensis (Bt) kills butterfly caterpillars: its toxin is released in the larval gut; other insects are unharmed.
- Trichoderma: free-living fungi of root ecosystems; biocontrol agents of several plant pathogens.
- ★ Must learn Baculoviruses (mostly genus Nucleopolyhedrovirus): species-specific, narrow-spectrum insecticides; suited to IPM.
- Biofertilisers: organisms that enrich the nutrient quality of soil; main sources are bacteria, fungi and cyanobacteria.
- ★ Must learn Rhizobium fixes nitrogen in root nodules of legumes (symbiotic); Azospirillum and Azotobacter fix it while free-living.
- ★ Must learn Glomus (mycorrhiza) passes phosphorus to the plant; cyanobacteria such as Anabaena, Nostoc and Oscillatoria fix nitrogen in paddy fields.
1. Biocontrol: Why We Need It
- Modern society has increasingly tackled pests and diseases with chemicals: insecticides and pesticides.
- ★ Exam imp These chemicals are toxic and extremely harmful to human beings and animals alike.
- They pollute our environment (soil and ground water), and also fruits, vegetables and crop plants.
- Our soil is also polluted by weedicides, which are used to remove weeds.
2. The Organic Farmer's Approach
- Biological control of pests and diseases relies on natural predation rather than introduced chemicals.
- ★ Exam imp A key belief of the organic farmer: biodiversity furthers health.
- The more variety a landscape has, the more sustainable it is.
- The organic farmer does not eradicate pests; they are kept at manageable levels by checks and balances within a living ecosystem.
- Eradicating pests may be possible, but it is undesirable, because beneficial predatory and parasitic insects depend on them as food or hosts.
- Thus, biocontrol measures greatly reduce our dependence on toxic chemicals and pesticides.
Chemical methods kill both useful and harmful life forms indiscriminately.
A holistic approach: it seeks to understand the webs of interaction among the many organisms of the field fauna and flora.
2.1 Planning biocontrol
- Become familiar with the various life forms that inhabit the field, both predators and pests.
- Learn their life cycles, patterns of feeding and the habitats they prefer.
- Use this knowledge to develop appropriate means of biocontrol.
3. Biocontrol Agents
3.1 Insect predators
- Ladybird: the very familiar beetle with red and black markings; it helps get rid of aphids.
- Dragonflies: help get rid of mosquitoes.
3.2 Bacillus thuringiensis (Bt)
- ★ Exam imp Bacillus thuringiensis, often written as Bt, is a microbial biocontrol agent that controls butterfly caterpillars.
- Bt is available in sachets as dried spores.
- The spores are mixed with water and sprayed onto vulnerable plants, such as brassicas and fruit trees.
- Insect larvae (caterpillars) eat them.
- In the gut of the larvae, the toxin is released.
- The larvae are killed; the bacterial disease kills the caterpillars but leaves other insects unharmed.
- In the last decade or so, genetic engineering has let scientists introduce B. thuringiensis toxin genes into plants.
- Such plants are resistant to attack by insect pests.
- Bt-cotton is one example; it is cultivated in some states of India.
3.3 Trichoderma
- Trichoderma: a fungus being developed as a biological control in the treatment of plant disease.
- Trichoderma species are free-living fungi, very common in root ecosystems.
- They are effective biocontrol agents of several plant pathogens.
3.4 Baculoviruses
- Baculoviruses: pathogens that attack insects and other arthropods.
- ★ Exam imp Most baculoviruses used as biological control agents belong to the genus Nucleopolyhedrovirus.
- They are excellent candidates for species-specific, narrow-spectrum insecticidal applications.
- They have no negative impact on plants, mammals, birds, fish or even non-target insects.
- This is especially desirable when beneficial insects are conserved in an integrated pest management (IPM) programme.
- It is also desirable when an ecologically sensitive area is being treated.
Each biocontrol agent has a specific target, and NEET pairs them.
- Bt kills only caterpillars (larvae) after they eat it; other insects are unharmed.
- Trichoderma acts against plant pathogens (diseases), not insects.
- Baculoviruses attack insects and other arthropods but spare plants, mammals, birds, fish and non-target insects.
Agent, type and target must be learnt as one unit.
| Biocontrol agent | Type | Controls |
|---|---|---|
| Ladybird | Insect (beetle) | Aphids |
| Dragonfly | Insect | Mosquitoes |
| Bacillus thuringiensis (Bt) | Bacterium | Butterfly caterpillars |
| Trichoderma | Fungus | Several plant pathogens |
| Baculoviruses (Nucleopolyhedrovirus) | Virus | Insects and other arthropods, species-specific |
Which beetle with red and black markings controls aphids?
Where in the larva is the Bt toxin released?
To which genus do most baculoviruses used in biocontrol belong?
4. Biofertilisers
- Environmental pollution is a major concern with our present-day lifestyles.
- Chemical fertilisers, used to meet the ever-increasing demand for farm produce, have added significantly to this pollution.
- Overuse of chemical fertilisers causes problems, so there is large pressure to switch to organic farming, that is, the use of biofertilisers.
4.1 Bacteria
- ★ Exam imp Rhizobium forms nodules on the roots of leguminous plants by a symbiotic association.
- These bacteria fix atmospheric nitrogen into organic forms, which the plant uses as a nutrient.
- Other bacteria fix atmospheric nitrogen while free-living in the soil: Azospirillum and Azotobacter.
- They enrich the nitrogen content of the soil.
Rhizobium. Lives in root nodules of leguminous plants.
Azospirillum and Azotobacter. Live free in the soil.
4.2 Fungi: mycorrhiza
- Mycorrhiza: a symbiotic association of a fungus with the roots of a plant.
- Many members of the genus Glomus form mycorrhiza.
- ★ Exam imp The fungal symbiont absorbs phosphorus from the soil and passes it to the plant.
Other benefits to plants with mycorrhiza
- Resistance to root-borne pathogens.
- Tolerance to salinity and drought.
- An overall increase in plant growth and development.
4.3 Cyanobacteria
- Cyanobacteria: autotrophic microbes widely distributed in aquatic and terrestrial environments.
- Many of them can fix atmospheric nitrogen, for example Anabaena, Nostoc and Oscillatoria.
- ★ Exam imp In paddy fields, cyanobacteria serve as an important biofertiliser.
- Blue-green algae (cyanobacteria) also add organic matter to the soil and increase its fertility.
- Today, many biofertilisers are available commercially in India.
- Farmers use them regularly to replenish soil nutrients and to reduce dependence on chemical fertilisers.
Which nutrient does the fungus in mycorrhiza pass to the plant?
What does the fungus gain from the mycorrhizal association?
Name two free-living nitrogen-fixing bacteria.
5. Exam Essentials
Pairs to Match
| Organism or term | Matches with |
|---|---|
| Ladybird | Aphids |
| Dragonflies | Mosquitoes |
| Bacillus thuringiensis | Butterfly caterpillars |
| Bt toxin genes in plants | Bt-cotton, resistant to insect pests |
| Trichoderma | Biocontrol of plant pathogens; root ecosystems |
| Baculoviruses | Insects and other arthropods |
| Nucleopolyhedrovirus | Genus of most baculoviruses used in biocontrol |
| Organic farmer's belief | Biodiversity furthers health |
| Rhizobium | Symbiotic nitrogen fixation in root nodules of legumes |
| Azotobacter and Azospirillum | Free-living nitrogen fixation in soil |
| Glomus | Mycorrhiza; phosphorus to the plant |
| Anabaena, Nostoc, Oscillatoria | Nitrogen-fixing cyanobacteria |
| Cyanobacteria | Important biofertiliser in paddy fields |
| Weedicides | Remove weeds; pollute soil |
- Bt kills caterpillars but leaves other insects unharmed.
- Baculoviruses have no negative impact on plants, mammals, birds, fish or non-target insects.
- Trichoderma controls plant pathogens, not insect pests.
- Azotobacter and Azospirillum are free-living, not symbiotic; Rhizobium is symbiotic.
- Glomus supplies phosphorus, not nitrogen.
- Cyanobacteria are autotrophic, unlike the other biofertilisers on this page.
- The organic farmer does not eradicate pests; they are kept at manageable levels.
Examples to Remember
| Group | Examples on this page |
|---|---|
| Predatory insects | Ladybird, dragonflies |
| Microbial biocontrol agents | Bacillus thuringiensis (bacterium), Trichoderma (fungus), baculoviruses such as Nucleopolyhedrovirus (virus) |
| Symbiotic nitrogen-fixing bacterium | Rhizobium |
| Free-living nitrogen-fixing bacteria | Azospirillum, Azotobacter |
| Mycorrhizal fungus | Glomus |
| Nitrogen-fixing cyanobacteria | Anabaena, Nostoc, Oscillatoria |
| Bt crop | Bt-cotton |
6. Quick Revision
- Biocontrol: biological methods to control plant diseases and pests.
- Insecticides and pesticides are toxic and pollute soil, ground water and food; weedicides pollute soil.
- Biological control relies on natural predation; biodiversity furthers health.
- Pests are kept at manageable levels, not eradicated, so predators and parasites survive.
- Know the field's predators and pests, their life cycles, feeding and habitats, to plan biocontrol.
- Ladybird controls aphids; dragonflies control mosquitoes.
- Bt spores are sprayed on brassicas and fruit trees; the toxin kills caterpillars in the gut.
- Bt toxin genes in plants give pest-resistant crops such as Bt-cotton.
- Trichoderma: free-living fungi of root ecosystems; control plant pathogens.
- Baculoviruses (Nucleopolyhedrovirus): species-specific, narrow-spectrum; safe for non-targets; useful in IPM.
- Biofertilisers enrich soil nutrients; sources are bacteria, fungi and cyanobacteria.
- Rhizobium: symbiotic nitrogen fixation in legume nodules; Azospirillum, Azotobacter: free-living.
- Glomus forms mycorrhiza, gives phosphorus, root-pathogen resistance, salinity and drought tolerance.
- Cyanobacteria (Anabaena, Nostoc, Oscillatoria) fix nitrogen and add organic matter in paddy fields.
7. Solved Examples
List I: A. Rhizobium, B. Azotobacter, C. Glomus, D. Anabaena
List II: I. Free-living nitrogen-fixing bacterium, II. Passes phosphorus to the plant, III. Symbiotic nitrogen fixation in root nodules, IV. Nitrogen-fixing cyanobacterium of paddy fields
Choose the correct answer:
(A) A-I, B-III, C-II, D-IV
(B) A-III, B-II, C-I, D-IV
(C) A-III, B-I, C-IV, D-II
(D) A-III, B-I, C-II, D-IV
Answer: (D). Rhizobium is symbiotic (III), Azotobacter free-living (I), Glomus supplies phosphorus (II) and Anabaena is a cyanobacterium (IV).
A. The Bt toxin is released in the gut of the insect larvae.
B. Baculoviruses harm birds and fish.
C. Trichoderma is a biocontrol agent of plant pathogens.
D. Dragonflies are used to get rid of aphids.
E. Most baculoviruses used in biocontrol belong to Nucleopolyhedrovirus.
Choose the correct answer:
(A) A, C and E only
(B) A, B and C only
(C) B, D and E only
(D) C, D and E only
Answer: (A). B is wrong: baculoviruses do not harm birds or fish. D is wrong: dragonflies control mosquitoes; the ladybird controls aphids.
A. The larvae eat the sprayed spores
B. The toxin is released in the larval gut
C. Dried spores are mixed with water and sprayed on plants
D. The larvae are killed
Choose the correct answer:
(A) A, C, B, D
(B) C, B, A, D
(C) C, A, B, D
(D) C, A, D, B
Answer: (C). Spraying (C), eating (A), release of the toxin in the gut (B), death of the larvae (D).
Statement II: Beneficial predatory and parasitic insects depend on pests as food or hosts.
Choose the correct answer:
(A) Both Statement I and Statement II are correct
(B) Both Statement I and Statement II are incorrect
(C) Statement I is correct but Statement II is incorrect
(D) Statement I is incorrect but Statement II is correct
Answer: (D). Pests are kept at manageable levels, not eradicated, precisely because predators and parasites need them.
(A) Absorption of phosphorus from the soil
(B) Resistance to root-borne pathogens
(C) Tolerance to salinity and drought
(D) Fixation of atmospheric nitrogen
Answer: (D). Glomus passes phosphorus, not fixed nitrogen, to the plant.
(A) tea gardens
(B) paddy fields
(C) desert soils
(D) orchards of fruit trees
Answer: (B). In paddy fields, nitrogen-fixing cyanobacteria are an important biofertiliser.
- Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.Answer: Biofertilisers such as Rhizobium, Azotobacter, Azospirillum, cyanobacteria and Glomus add nitrogen or phosphorus to the soil, replacing chemical fertilisers. Biocontrol agents such as Bt, Trichoderma and baculoviruses control pests and pathogens, replacing chemical pesticides.
- Find out the role of microbes in the soil.Answer: Microbes fix nitrogen (Rhizobium, Azotobacter, cyanobacteria), supply phosphorus through mycorrhiza (Glomus) and protect roots from pathogens (Trichoderma). Beyond this page, soil microbes also decompose dead matter and release its nutrients.
- How do biofertilisers enrich the fertility of the soil?Answer: Rhizobium fixes nitrogen in root nodules of legumes; Azospirillum and Azotobacter fix it in the soil; Glomus passes phosphorus to plants; cyanobacteria fix nitrogen and add organic matter.
- Match List I with List II.
List I: A. Ladybird, B. Dragonflies, C. Bacillus thuringiensis, D. Trichoderma
List II: I. Plant pathogens, II. Mosquitoes, III. Aphids, IV. Butterfly caterpillars
(A) A-III, B-II, C-IV, D-I
(B) A-II, B-III, C-IV, D-I
(C) A-III, B-II, C-I, D-IV
(D) A-IV, B-II, C-III, D-IAnswer: (A). Ladybird and aphids, dragonflies and mosquitoes, Bt and caterpillars, Trichoderma and plant pathogens. - Read the statements.
A. Biofertilisers enrich the nutrient quality of soil.
B. Azospirillum forms root nodules on legumes.
C. Cyanobacteria are autotrophic.
D. Glomus forms mycorrhiza.
Choose the correct answer:
(A) A, B and C only
(B) A, C and D only
(C) B, C and D only
(D) A, B and D onlyAnswer: (B). Azospirillum is free-living; Rhizobium forms the root nodules. - Arrange the steps of planning biocontrol in order.
A. Develop appropriate means of biocontrol
B. Become familiar with the predators and pests in the field
C. Learn their life cycles, feeding patterns and habitats
(A) A, B, C
(B) B, A, C
(C) B, C, A
(D) C, B, AAnswer: (C). Know the organisms, study their biology, then design the control. - Which of the following statements about baculoviruses is NOT correct?
(A) They attack insects and other arthropods
(B) They are suited to narrow-spectrum applications
(C) They harm non-target insects
(D) They are desirable in ecologically sensitive areasAnswer: (C). Baculoviruses have no negative impact on non-target insects.
Common Mistakes to Avoid
- Calling Azotobacter or Azospirillum symbiotic. Correct: both are free-living; Rhizobium is symbiotic.
- Writing that Glomus fixes nitrogen. Correct: it absorbs phosphorus and passes it to the plant.
- Saying Bt kills all insects. Correct: it kills caterpillars that eat it and leaves other insects unharmed.
- Using Trichoderma as an insecticide. Correct: it controls plant pathogens.
- Thinking baculoviruses harm birds, fish or mammals. Correct: they are species-specific and safe for non-targets.
- Swapping the predators. Correct: ladybird controls aphids; dragonflies control mosquitoes.
- Defining organic farming as eradicating pests. Correct: pests are kept at manageable levels.
- Calling cyanobacteria fungi or heterotrophs. Correct: they are autotrophic bacteria (blue-green algae).
Frequently Asked Questions
What is biocontrol and why is it preferred to chemical pesticides?
Biocontrol is the use of biological methods to control plant diseases and pests. Chemical insecticides and pesticides are toxic to humans and animals and pollute soil, ground water and food, while weedicides pollute the soil. Biocontrol relies on natural predators, microbes and checks and balances in the ecosystem, so it greatly reduces our dependence on these chemicals.
Why does the organic farmer not eradicate pests?
The organic farmer believes that biodiversity furthers health. Pests are kept at manageable levels rather than eradicated, because beneficial predatory and parasitic insects depend on them as food or hosts. Without pests, these useful insects could not survive, and the natural checks and balances of the field would break down.
How does Bacillus thuringiensis kill caterpillars?
Dried spores of Bacillus thuringiensis (Bt), sold in sachets, are mixed with water and sprayed on plants such as brassicas and fruit trees. Butterfly caterpillars eat them, the toxin is released in the larval gut, and the larvae are killed. Other insects are unharmed. Bt toxin genes have also been put into crops such as Bt-cotton.
Why are baculoviruses good biocontrol agents?
Baculoviruses attack insects and other arthropods, and most of those used in biocontrol belong to the genus Nucleopolyhedrovirus. They are species-specific and narrow in spectrum, with no harmful effect on plants, mammals, birds, fish or non-target insects. This makes them ideal for integrated pest management and for ecologically sensitive areas.
What is the role of Trichoderma in biocontrol?
Trichoderma species are free-living fungi that are very common in root ecosystems. They are being developed as a biological control for plant disease, because they are effective biocontrol agents of several plant pathogens. Unlike Bt and baculoviruses, they act against disease-causing organisms of plants, not against insect pests.
What are biofertilisers? Name their main sources.
Biofertilisers are organisms that enrich the nutrient quality of the soil. Their main sources are bacteria, fungi and cyanobacteria. Examples include Rhizobium, Azotobacter and Azospirillum among bacteria, Glomus among fungi, and Anabaena, Nostoc and Oscillatoria among cyanobacteria. Farmers use them to reduce chemical fertilisers.
What is mycorrhiza and how does it help plants?
Mycorrhiza is a symbiotic association between a fungus and plant roots; many members of the genus Glomus form it. The fungus absorbs phosphorus from the soil and passes it to the plant. Such plants also resist root-borne pathogens, tolerate salinity and drought, and show an overall increase in growth and development.
Which points on biofertilisers and biocontrol does NEET ask most?
NEET most often pairs each agent with its target or nutrient: ladybird and aphids, dragonflies and mosquitoes, Bt and caterpillars, Trichoderma and plant pathogens, baculoviruses and Nucleopolyhedrovirus, Glomus and phosphorus, and symbiotic versus free-living nitrogen fixers. It follows the NCERT examples closely, so learn each name exactly.
Previous year questions on Biofertilisers and Biocontrol Agents
2 questions from past papers, each with a step-by-step solution.
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