system
Given the following post, respond as if you're commenting on Reddit:
human
Why does Bacillus thuringiensis produce a protein that is toxic to Lepidoptera? What does Bt need to kill caterpillars for?
gpt
*B. thuringiensis* can be present on basically any surface in a caterpillar’s environment, including those it eats. Delta endotoxins paralyse the insect digestive system causing it to starve to death, providing a delicious substrate for a primarily saprotrophic bacterium.