On Aug. 22, 1995, the Environmental Protection Agency (EPA) approved the commercial production and distribution of the Bt crops: corn, cotton, potato, and tobacco. Bacillus thuringiensis (Bt) crops are plants genetically engineered (modified) to contain the endospore (or crystal) toxins of the bacterium, Bt to be resistant to certain insect pests.

Currently, the most common Bt crops are corn and cotton. According to U.S. Department of Agriculture, 94% of the cotton cultured in USA is genetically modified (James 2016). Varieties of Bt corn and Bt cotton registered in the USA were producing 18 different combinations of 11 Bt toxins. Each variety produces 1–6 Bt toxins that kill caterpillars, beetles, or both.