Microbes as Biocontrol Agents – Uses, Advantages and Disadvantages

Do you know what pests are? How to control these? You all know that generally, pesticides are used to kill pests, but pesticides have many harmful effects on our environment. The use of biological methods or techniques to control plant diseases and pests is called biological pest control, whereas the beneficial organisms, i.e., specific useful organisms that are used and cultured to kill the pests, are known as biocontrol agents. But why Microbes as Biocontrol Agents? Why can’t we use chemicals as biocontrol agents? To know more about this scroll through the article.

What are Biocontrol Agents?

Biocontrol refers to the use of biological methods for controlling pests and plant diseases. Chemical-based insecticides and pesticides are extremely harmful to human beings and also pollute the surrounding environment. The use of biocontrol measures will greatly decrease our dependence on toxic chemicals and pesticides.

Fig: Microbes as Biocontrol Agents

Biopesticides are certain pesticides derived from natural or biological agents like plants, animals, bacteria, fungi, viruses, etc., to destroy or control weeds, insects and pathogens.
According to the nature of organisms, Biopesticides are of two types: microbial pesticides and biochemical pesticides.

Microbial Pesticides

1. Microbial pesticides are the ones that come from naturally occurring or genetically altered bacteria, algae, fungus, viruses or protozoans.
2. These microbial pesticides have become an alternative to chemical insecticides with increased target specificity and ecological safety so that they are used either directly or in combination with other pest management programmes.
3. A microbial toxin is a biological toxin that is derived from a microorganism, such as a bacterium or a fungus.
4. The pathogenic effect of those microorganisms on the target pests are species-specific.
5. The effect of microbial entomopathogens is due to the invasion through the gut of the insect, which is followed by multiplication of the pathogen resulting in the death of the host organism, for example, insects.
6. Most of the toxins that are produced by microbial pathogens have been identified as peptides, but they vary greatly in terms of structure, specificity and toxicity.
7. These microbes as biocontrol agents are useful and efficient, and safe for humans and other non-target organisms. Hence, the microbial agents are highly specific against target pests, so these promote and play a major role in the survival of beneficial insects in treated agricultural crops.

Characteristics of Effective Biocontrol Agents

These highly effective bio-control agents must fulfil certain criteria like:
1. Should be able to compete and live longer in soil and host tissue.
2. Should be able to colonize and proliferate.
3. Should be non-pathogenic to the host plant and environment.
4. Production must result in biomass with an excellent shelf life.
5. Delivery and application must permit full expression of the agent.

How Microbes are Used as Biocontrol Agents?

Some of the microbes that are used as biocontrol agents are given below:

a. Bacterial Pesticide

i. The most commonly used microbial pesticides are subspecies and strains of Bacillus thuringiensis.
ii. Bacillus thuringiensis \(\left( {{\rm{Bt}}} \right)\) is a gram-positive bacterium that is used to get rid of butterfly caterpillars.
iii. In this, the dried spore of Bacillus thuringiensis is mixed with water and sprayed onto vulnerable plants such as Brassica and fruit trees.
iv. These spores are eaten by the insect larvae and in the gut of the larvae, the toxin is released, and the larvae get killed.

Fig: Bacillus thuringiensis

b. Viral Pesticides

i. There are more than \(1600\) different viruses that infect around \(1100\) species of mites and insects.
ii. A special group of viruses known as baculovirus, to which about \(100\) insect species are susceptible, accounts for more than \({\rm{10\% }}\) of all insect pathogenic viruses. Baculoviruses are rod-shaped particles that contain DNA. Baculoviruses are pathogenic agents that attack insects and other members of the phylum Arthropoda.
iii. The majority of baculoviruses that are used as biological control agents belong to the genus Nucleopolyhedrovirus.
iv. These viruses are good agents for species-specific, narrow spectrum, insecticidal applications.

c. Protozoan Pesticides

i. These protozoan pathogens naturally infect a wide range of insect hosts.
ii. Even though these pathogens can kill their insect hosts, many are important for their chronic and debilitating effects.
iii. One of the important and common consequences of protozoan infection is a reduction in the number of offspring produced by infected insects.
iv. Although protozoan pathogens play a significant role in the natural limitation of insect populations, few appear to be suited for development as insecticides.

d. Fungal Pesticides

i. Beauveria bassiana is an entomopathogenic fungus that is responsible for causing white muscardine disease in a range of insects, including whiteflies, thrips, grasshoppers, aphids and certain types of beetles.
ii. B. bassiana spores need to come in contact with a host. Once the host insect is infected, the fungus grows inside of the insect rapidly, feeding on the nutrients present in the host’s body and producing toxins in turn. When the host dies, the B. bassiana covers the carcass in a layer of white mould that produces more infective spores.

Fig: Image (a) Beauveria bassiana Fungus on the Petri Plate; Image (b) Represents Colonization of Fungus on the Pests

iii. Trichoderma is known to exhibit biocontrol over several plant pathogens.

Fig: Trichoderma

Microbial Herbicide

1. Herbicides that are used to control unwanted plant growth are also called weedkillers.
2. The microbial origin of herbicides has developed drastically in the last few years, and it is now contributing as an alternative to chemical herbicides.
3. The microbial herbicides are effective enough to control weeds and it is applied in many countries.

Do You Know This!!

Another natural insecticide called Pyrethrum, extracted from the flower head of Chrysanthemum cinerariifolium, is used in organic farming practices. These plants grown near crops repel insects due to their insecticidal properties.

Fig: Chrysanthemum cinerariifolium

Advantages of Microbes as Biocontrol Agents

These have no negative impacts on plants, mammals, fish, birds or even on non-target insects. This is specifically desirable when beneficial insects are being conserved to aid in the overall Integrated Pest Management (IPM) Programme or when an ecologically sensitive area is being treated.

Some of the advantages are as follows:
1. These are cost-effective.
2. These biocontrol agents reduce the use of chemicals and other pesticides.
3. As it is easily available, effective in all seasons and easy to use.
4. They are environment friendly and also do not cause any side effects.

Disadvantages of Microbes as Biological Agents

Some of the disadvantages are as follows:
1. The high specificity against the target disease and pathogen may require multiple microbial pesticides.
2. It may affect product quality.
3. Pest is not completely removed by these biocontrol agents.
4. These are not very effective for short scale applications.

Summary

Through this article, we understood that microbes play a very important role in controlling certain pests, insects and help in getting a high agricultural yield, and these are not harmful to the environment as they do not cause any pollution. This method relies on natural predation, which is in contrast to the modern-day practice of killing insects and pests with pesticides and insecticides.

Some microbes, such as Trichoderma, a-living fungus, Baculoviruses of genus Nucleopolyhedrovirus in plant roots, acts as a bio-control agent for various plant pathogens and pests, respectively. This may be the important reason that microbial insecticides are being developed more as biological control agents during the last few decades.

Frequently Asked Questions (FAQs) on Microbes as Biocontrol Agents

The most frequently asked questions about microbes as biocontrol agents are answered here:

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