8.5. Microbes as Biocontrol Agents

Biocontrol refers to the use of biological methods for controlling plant diseases and pests. In modern society, these problems have been tackled increasingly by the use of chemicals – by use of insecticides and pesticides. These chemicals are toxic and extremely harmful, to human beings and animals alike, and have been polluting our environment (soil, ground water), fruits, vegetables and crop plants. Our soil is also polluted through our use of weedicides to remove weeds.

Biocontrol is an approach to managing pests and diseases using natural methods instead of chemicals. Traditionally, farmers relied heavily on chemical pesticides, which can be harmful not only to pests but also to humans and animals, and they contribute to environmental pollution. The shift towards biocontrol looks to implement safer, more sustainable ways of pest management.

Think of biocontrol like using a natural remedy instead of medicine filled with chemicals. Just as using honey and lemon can soothe a sore throat without the side effects of chemical medications, biocontrol aims to minimize harm while effectively managing pest populations.

In agriculture, there is a method of controlling pests that relies on natural predation rather than introduced chemicals. A key belief of the organic farmer is that biodiversity furthers health. The more variety a landscape has, the more sustainable it is.

This concept revolves around the idea that a diverse ecosystem can naturally regulate pest populations. By maintaining a variety of plants and animals in farmland, beneficial insects that prey on harmful pests can thrive, creating a balanced environment that limits pest outbreaks without pesticides.

Consider a forest: it has a wide variety of plants and animals. If one species of insect tries to overpopulate, there are plenty of natural predators, like birds and other insects, that will keep it in check. Similarly, farmers can create their own 'mini-ecosystems' to foster these natural predator-prey relationships.

An example of microbial biocontrol agents that can be introduced in order to control butterfly caterpillars is the bacteria Bacillus thuringiensis (often written as Bt). These are available in sachets as dried spores which are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees, where these are eaten by the insect larvae. In the gut of the larvae, the toxin is released and the larvae get killed.

Bacillus thuringiensis (Bt) is a type of bacteria that produces toxins harmful to certain insect larvae, like caterpillars. Farmers can apply Bt in controlled amounts, allowing it to target only the harmful pests without affecting beneficial insects. This application is both safe and environmentally friendly.

Imagine using a targeted medicine that only affects sick cells without harming healthy ones. Similarly, when Bt is sprayed on crops, it affects only the caterpillars—like a precision-guided treatment—and leaves other insects and plants unharmed, promoting a healthier ecosystem.

Because of the development of methods of genetic engineering in the last decade or so, the scientists have introduced B. thuringiensis toxin genes into plants. Such plants are resistant to attack by insect pests. Bt-cotton is one such example, which is being cultivated in some states of our country.

Through genetic engineering, scientists can insert genes from Bacillus thuringiensis into the DNA of crops like cotton, giving them the ability to produce their own pest-deterring toxins. This biotech approach reduces the need for external pesticide applications and enhances crop resilience against specific pests.

It's like giving plants a superpower to fight pests. Just as superheroes have powers to protect themselves, genetically modified plants can fend off insect attacks, helping farmers grow their crops with less dependency on harmful pesticides.

A biological control being developed for use in the treatment of plant disease is the fungus Trichoderma. Trichoderma species are free-living fungi that are very common in the root ecosystems. They are effective biocontrol agents of several plant pathogens.

Trichoderma is a beneficial fungus that can suppress plant diseases caused by harmful fungi and can promote plant growth. By enhancing the health of roots and competing with harmful pathogens, Trichoderma acts as a natural form of pest and disease control.

Think of Trichoderma as a friendly neighbor in a community who helps keep the area safe and clean. Just as a neighbor might help keep other residents healthy by removing nuisances and promoting a better environment, Trichoderma helps plants grow strong while reducing the risk of diseases.

Baculoviruses are pathogens that attack insects and other arthropods. The majority of baculoviruses used as biological control agents are in the genus Nucleopolyhedrovirus. These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications.

Baculoviruses specifically target certain insect pests and do not affect other forms of life, making them ideal for pest management strategies. Because they are narrow-spectrum, they preserve beneficial insects, providing a balanced approach to pest control.

Imagine a precision laser that can cut specific materials without affecting those around it. Baculoviruses act similarly—they can target harmful insects without disrupting the entire ecosystem, thereby protecting beneficial species and maintaining biodiversity.

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