Biology · Microbes in Human Welfare · NEET
It is a biocontrol agent, NOT a biofertiliser. Bt is a bacterium that kills insect pests (butterfly caterpillars). Biofertilisers like Rhizobium, Azospirillum and cyanobacteria (Nostoc, Anabaena) add nutrients to soil. NEET options often mix these two lists to confuse you. Remember: Bt fights pests, it does not feed the plant.
Bt is sold as dried spores in sachets. You mix the spores with water and spray them on plants such as brassicas and fruit trees. Insect larvae eat the sprayed leaves. Inside the gut of the larvae the toxin is released, and the larvae get killed. The bacterial disease kills the caterpillars but leaves other insects unharmed. (Note: in Ch 8 NCERT does not go into the alkaline-pH detail; that pore-forming detail belongs to Bt cotton in Biotechnology, Ch 10.)
In Microbes in Human Welfare (Ch 8), whole living Bt bacteria are sprayed as spores to control caterpillars directly. In Bt cotton (Ch 10, Biotechnology), only the Bt toxin GENE is cloned from the bacterium and inserted into the plant, so the plant itself makes the toxin. Both use the same bacterium, but one sprays the microbe and the other engineers the gene into the crop.
It is a bacterium. In the NCERT trio of microbial biocontrol agents, Bt is the bacterium, Trichoderma is a fungus (controls plant pathogens), and Baculovirus (Nucleopolyhedrovirus) is a virus (attacks insects and arthropods). NEET loves to swap these categories, so fix them clearly.
As a sprayed biocontrol agent in Ch 8, Bt is used to control butterfly caterpillars (larvae), and it leaves other insects unharmed. This selectivity is why it is a good biocontrol choice. (Bt STRAINS as a group can produce proteins toxic to lepidopterans, coleopterans and dipterans, but that wider point is discussed under Bt cotton in Ch 10.)
Select the correct group of biocontrol agents.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is used as a microbial biocontrol agent to control butterfly caterpillars (insect larvae) on plants like brassicas and fruit trees, without harming other insects.
It is available in sachets as dried spores. The spores are mixed with water and sprayed onto vulnerable plants, where insect larvae eat them and die.
Bacillus thuringiensis (bacterium), Trichoderma (fungus) and Baculovirus / Nucleopolyhedrovirus (virus). This trio is a very common NEET match/group question.
Bt kills only the target caterpillars and leaves other insects unharmed, so it does not damage useful predators or pollinators the way broad chemical pesticides do.
No. Bt biocontrol (Ch 8) sprays the living bacterium. Bt cotton (Ch 10) puts only the Bt toxin gene into the cotton plant using genetic engineering, so the plant makes the toxin itself.
