Bacillus thuringiensis kurstaki (Bt kurstaki) is a naturally occurring bacterium that is commonly used as a biological pesticide. It produces proteins that are toxic to certain insect larvae, particularly those of moths and butterflies. When these insects ingest the bacteria, the proteins disrupt their digestive systems, leading to death. This makes Bt kurstaki an effective tool for controlling pest populations in agriculture. Farmers often apply Bt kurstaki to crops like corn and cotton to protect them from harmful pests while minimizing the impact on beneficial insects. As a biological control agent, it is considered safer for the environment and human health compared to chemical pesticides.