How does Bt toxin kill the larvae of certain insects ?

Options

A. by binding of activated toxin on mid gut epithelial cells, creating pores, leading to swelling and lysis
B. By stopping transcription of larval cells
C. By altering central dogma taking place in the cells of gut of larva
D. by stopping protein synthesis

Answer

**Step-by-Step Solution:**

1. **Introduction to Bt Toxin:**
- Bt toxin is a biotoxin produced by the bacterium *Bacillus thuringiensis*. It is commonly found in soil and is known for its insecticidal properties.

2. **Types of Toxins Produced:**
- *Bacillus thuringiensis* produces two types of toxic proteins during its late exponential growth phase: Cry proteins (Cry toxins) and Cyt proteins (Cyt toxins).

3. **Inactivity of Toxin:**
- When these toxins are produced, they exist in an inactive form known as protoxins. This means they do not harm the bacteria itself or other organisms until activated.

4. **Ingestion by Insects:**
- When an insect larva ingests the Bt toxin (protoxin), it travels to the insect's midgut.

5. **Activation in the Midgut:**
- The midgut of the insect has an alkaline pH (around 11). This alkaline environment activates the protoxin, converting it into its active form.

6. **Mechanism of Action:**
- The activated toxin binds to the epithelial cells of the midgut. This binding creates pores in the cell membranes of these cells.

7. **Consequences of Pore Formation:**
- The formation of pores leads to the swelling of the midgut epithelial cells. Eventually, this swelling causes the cells to lyse (burst), leading to the death of the larva.

8. **Conclusion:**
- Therefore, the correct mechanism by which Bt toxin kills the larvae of certain insects is by binding to the midgut epithelial cells, creating pores that lead to swelling and lysis of the cells.

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