Bt corn is a genetically modified organism that contains a gene from bacteria that live in soil. this inserted gene allows the corn to kill the corn borer caterpillar

The inserted gene from the bacteria (Bacillus thuringiensis) produces a protein (Bt delta endotoxin) which kills the corn borer caterpillar by binding to the gut wall of the insects when the insects ingest a part of the plant that contains this protein. The insect would stop feeding immediately this protein binds to the gut wall of the insect, which leads to the eventual death of the corn borer caterpillar as the gut wall breaks down.