Biology · Microbes in Human Welfare · NEET
The bacterium Bacillus thuringiensis (written as Bt). It is sold in sachets as dried spores. You mix the spores with water and spray them on plants like brassicas (cabbage family) and fruit trees. When the insect larvae eat the sprayed leaves, the toxin is released in their gut and kills the caterpillars. Other insects are left unharmed, so it is a targeted, safe method.
Trichoderma is a fungus, not a bacterium. NEET loves this trap. Trichoderma species are free-living fungi that are very common in the root ecosystems (soil near roots). They are effective biocontrol agents of several plant pathogens (plant diseases), not of insects.
Baculoviruses are viruses that attack insects and other arthropods. Most baculoviruses used as biological control agents belong to the genus Nucleopolyhedrovirus. They are species-specific and narrow spectrum, meaning they kill only the target pest. They have no bad effect on plants, mammals, birds, fish, or even non-target (helpful) insects, so they are ideal for Integrated Pest Management (IPM).
No. Ladybird (a beetle with red and black markings) and Dragonflies are biocontrol agents but they are insects, not microbes. Ladybird controls aphids and Dragonfly controls mosquitoes. NCERT lists them under biological control, but the question stem must say 'microbial biocontrol agent' for you to pick Bt, Trichoderma, or Baculovirus instead.
Bt spray uses the whole living bacterium Bacillus thuringiensis as dried spores sprayed on plants; the toxin is released only inside the larva's gut. Bt cotton is a genetically modified plant into which the Bt toxin gene has been inserted, so the plant itself makes the toxin. Bt spray is classic biocontrol (Ch 8); Bt cotton is biotechnology (Ch 10).
When larvae eat the Bt spores, the inactive protoxin is converted into active toxin by the alkaline (high) pH of the insect gut. The active toxin makes pores in the midgut cells, causing the cells to swell, burst, and the insect dies. Because the toxin needs a specific gut environment, it kills only certain larvae (like caterpillars) and leaves other insects unharmed.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Biocontrol is the use of biological methods (living organisms) to control plant diseases and pests, reducing our dependence on toxic chemical pesticides and insecticides.
Bacillus thuringiensis (bacterium, for caterpillars), Trichoderma (fungus, for plant pathogens), and Baculovirus / Nucleopolyhedrovirus (virus, for insects).
They are species-specific and narrow spectrum. They have no negative impact on plants, mammals, birds, fish, or non-target beneficial insects, which is ideal for Integrated Pest Management (IPM) and ecologically sensitive areas.
Ladybird (a beetle) controls aphids, and Dragonfly controls mosquitoes. Both are insects, not microbes.
The genus Nucleopolyhedrovirus.
