Resistance to Bt crops: Lessons from the first 30 years

Crops genetically engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have improved pest management and reduced reliance on insecticide sprays. However, evolution of practical resistance by some pests has reduced the efficacy of Bt crops. Global resistance monitoring data were analyzed for 24 pest species based on the first 30 years of cultivation of Bt crops. The cases of practical resistance rose from 3 in 2005 to 31 in 2025. Practical resistance has been documented in some populations of 11 pest species (nine lepidopterans and two coleopterans), collectively affecting nine widely used crystalline (Cry) Bt toxins in eight countries.  Conversely, 29 cases reflect no decrease in susceptibility to Bt crops in populations of 15 pest species in nine countries.  The remaining 22 cases are early warnings of resistance, which entail genetically based decreases in susceptibility without evidence of reduced field efficacy. The early warnings involve four Cry toxins and the Bt vegetative insecticidal protein Vip3Aa. Factors favoring sustained susceptibility include abundant refuges of non-Bt host plants and recessive inheritance of resistance. Bt cotton and releases of over 11 billion sterile moths helped to eradicate from the continental U.S. the invasive pink bollworm (Pectinophora gossypiella), which had plagued cotton growers in the U.S. for nearly a century. This eliminated insecticide use against this pest, enhanced IPM, helped to reduce insecticide use in cotton by 82%, and saved growers an estimated $384 million from 2014 to 2025.