Q.What is meant by the term bio-pesticide? Name and explain the mode of action of a popular bio-pesticide.

Biopesticides are biological agents—microorganisms or their products—used to control pests, diseases, and weeds in an eco-friendly manner, without the harmful effects of chemical pesticides. They offer targeted action and leave no toxic residues in the environment or food chain.

Bacillus thuringiensis (Bt) is the most popular biopesticide. Several strains of this bacterium produce different insecticidal crystal proteins during sporulation. The Bt toxin exists as inactive protoxin crystals in the bacterial spore. When a susceptible insect larva (like butterfly or moth caterpillars) ingests these spores along with plant material, the alkaline pH of the insect gut solubilizes the crystals and activates the toxin. The activated toxin binds to specific receptors on the midgut epithelial cells, creating pores in the cell membrane. This leads to cell swelling, lysis, and eventually the death of the insect larva. The tox …

The term "bio-pesticide" refers to pest-control agents derived from natural materials: living organisms (bacteria, fungi, viruses), their metabolic products, or biochemicals extracted from plants and animals. Unlike synthetic chemical pesticides that persist in the environment and accumulate in food chains, bio-pesticides offer a targeted, eco-friendly alternative. They work by exploiting specific biological mechanisms—parasitism, predation, toxin production—that harm only the target pest while leaving beneficial insects, soil microbes, and humans largely unaffected.

Bio-pesticides fit into three broad categories. Microbial pesticides contain microorganisms (bacteria, fungi, viruses) that infect and kill pests. Biochemical pesticides are naturally occurring substances—pheromones, plant extracts, insect hormones—that disrupt pest behaviour or physiology without direct toxicity. Plant-incorporated protectants are genetic material introduced into crops so the plant itself manufactures the pesticidal substance (though this edges into genetic modification). The appeal is clear: they degrade quickly, leave minimal residues, and reduce the chemical load on farmland.

Bacillus thuringiensis: the flagship bio-pesticide

The bacterium Bacillus thuringiensis, universally abbreviated as Bt, stands as the most successful and widely adopted bio-pesticide in agriculture. Discovered in the early twentieth century, Bt is a soil-dwelling, spore-forming bacterium that produces crystalline protein toxins lethal to specific insect larvae—particularly caterpillars (lepidopteran larvae), mosquito larvae, and some beetle larvae.

Mode of action

Bt's killing mechanism is elegantly specific. During sporulation, the bacterium synthesizes protein crystals called delta-endotoxins (or Cry proteins) alongside its spores. When an insect larva ingests Bt spores—usually by feeding on sprayed plant leaves—the alkaline environment of the insect's gut dissolves these crystals. The released proteins are then activated by gut enzymes, transforming into toxic fragments.

These toxins bind to specific receptor sites on the epithelial cells lining the insect's midgut. Binding creates pores in the cell membrane, disrupting the gut's osmotic balance. Water and ions flood into the cells, causing them to swell, lyse, and disintegrate. The gut wall breaks down, the larva stops feeding within hours, and paralysis follows. Gut bacteria spill into the body cavity, leading to septicemia and death within a day or two. …

Method — define the category, then trace ONE example's full mechanism

Definition: a biopesticide is a biological agent (organism or its product) used to control pests, in place of a synthetic chemical. …