Bt (Bacillus thuringiensis) is a bacterium found in soils throughout the world. It naturally produces crystal-like proteins (Cry proteins) that selectively kill a few specific insect species.
Bt corn, a.k.a. transgenic corn, is corn that has been modified to produce the insecticidal proteins that occur naturally in Bt. There are several strains of Bt, and each produces different insecticidal proteins, in the form of crystals (Cry proteins), which control specific groups of insect pests. Most of the Bt corn hybrids marketed in Canada are targeted either against the European corn borer (i.e. Cry1Ab or Cry1F protein) or the corn rootworm (i.e. Cry3Bb, Cry 34Ab1/Cry 35Ab1 or mCry 3A protein) or both (i.e. stacked hybrids containing Cry protein active against ECB and Cry protein active against CRW).