Day: April 17, 2025

Bt is a bacterium that is found naturally in soils throughout the world. To reproduce, Bt makes spores that grow into new bacteria. Bt spores have proteins that are toxic to insect larvae when eaten.² Because Bt comes from a natural source, it is called a biopesticide. In general, biopesticides tend to pose fewer risks than typical human-made pesticides.

There are many types of Bt. Each type or strain affects different insect groups. Target insects include the beetle family, the fly family including mosquitoes, and the butterfly family. It is used to kill beetles and the larvae of mosquitoes, black flies, and moths.^2,3,4 Bt is also toxic to nematodes.⁵

Bt has been registered for use in pesticides by the U.S. Environmental Protection Agency (U.S. EPA) since 1961. The U.S. EPA requires routine testing to ensure that unwanted toxins and bacteria are not present.² Some of these unwanted toxins may be harmful to non-target animals and people.⁶