Question

Why does the Bt toxin not kill the bacterium that produces it but kill the insect that ingests it?

Answer 1

Bt toxin is produced by a soil bacterium called Bacillus thuringiensis. This toxin does not kill the bacteria because when it is present in the bacteria, it is in an inactive and crystalline form. It becomes active and toxic when it is consumed by insects such as lepidopterans, coleopterans (beetles) and dipterans (flies / mosquitoes).

The activated toxin (delta endotoxins) binds to the epithelial cells in the midgut of an insect and creates pores that cause lysis and swelling, eventually killing the insect.