Bacillus thuringiensis (Bt) toxins are effective because they produce proteins that disrupt the gut of susceptible larvae after ingestion.

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Multiple Choice

Bacillus thuringiensis (Bt) toxins are effective because they produce proteins that disrupt the gut of susceptible larvae after ingestion.

The main idea is that Bt toxins kill by a gut-targeted mechanism after the insect ingests them. Bacillus thuringiensis produces crystalline (Cry) insecticidal proteins that, once in the larval gut, are solubilized and activated by gut proteases. The activated toxins bind to specific receptors on the midgut epithelial cells and insert into the membrane to form pores. This disrupts ion balance and cell integrity, leading to gut failure, septicemia, and death. The specificity comes from the need for compatible gut receptors and conditions in susceptible larvae, plus the requirement of ingestion for activation. Other insecticides act through different modes—poisoning the nervous system, repelling insects with plant cues, or blocking chitin synthesis to prevent molting—but Bt’s effect is directly through gut disruption after ingestion.

The main idea is that Bt toxins kill by a gut-targeted mechanism after the insect ingests them. Bacillus thuringiensis produces crystalline (Cry) insecticidal proteins that, once in the larval gut, are solubilized and activated by gut proteases. The activated toxins bind to specific receptors on the midgut epithelial cells and insert into the membrane to form pores. This disrupts ion balance and cell integrity, leading to gut failure, septicemia, and death. The specificity comes from the need for compatible gut receptors and conditions in susceptible larvae, plus the requirement of ingestion for activation. Other insecticides act through different modes—poisoning the nervous system, repelling insects with plant cues, or blocking chitin synthesis to prevent molting—but Bt’s effect is directly through gut disruption after ingestion.

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