Truth: GM Bt crops are not specific to pests but affect a range of organisms

Myth at a glance

The Bt toxins engineered into GM Bt crops are not specific to target pests and close relatives but can negatively affect a range of non-target organisms, including beneficial insects that help protect crops, beneficial soil organisms, and mammals.

GMO proponents claim that Bt crops only affect target pests and their close relatives. Regulators have uncritically accepted this claim and allowed the commercialization of Bt crops with a minimum of oversight. But research studies show that the claim is false.

GM Bt crops harm non-target and beneficial organisms

GM Bt insecticide-producing crops have been found to have toxic effects on non-target insect populations when Bt crop fields are compared with insecticide-free fields.1 Non-target insects that are adversely affected by Bt crops include monarch2,3 and swallowtail butterflies,4 and beneficial pest predators such as ladybirds5,6 and lacewings7 (see Myth 2.3).

Bt crops have been found to have more negative than positive impacts on the natural enemies of crop pests.8 Bt toxin has been found to negatively impact bee learning behaviour, interfering with the bees’ ability to find nectar sources for food.9

GM crops containing Bt toxins have had toxic effects on mammals in animal feeding studies10,11,12,13,14(see Myth 3.1).

GM Bt crops negatively impact soil organisms

Mycorrhizal fungi benefit plants by colonizing their roots, helping them take up nutrients, resist disease, and tolerate drought. A study comparing Bt and non-Bt maize found a lower level of mycorrhizal colonization in the roots of GM Bt maize plants. Residues of Bt maize plants, ploughed under at harvest and kept mixed with soil for up to four months, suppressed soil respiration (carbon dioxide production), markedly altered bacterial communities, and reduced mycorrhizal colonization.15A separate field study on Bt maize residues ploughed into soil after harvest confirmed that Bt toxin resisted breakdown and persisted in soil for months.16

Arbuscular mycorrhizal fungi (AMF) are beneficial fungi that penetrate the root cells of the host plant. GM Bt maize was found to have decreased arbuscular mycorrhizal fungi (AMF) colonization of roots, compared with non-GM maize.17,18

Bt crops harm aquatic organisms

A study conducted in Indiana, USA found that Bt insecticide released from GM Bt maize was polluting 25% of streams tested.19 GM Bt maize biomass is toxic to aquatic organisms.20 Water fleas (an organism often used as an indicator of environmental toxicity) fed GM Bt maize showed toxic effects including reduced fitness, higher mortality, and impaired reproduction.21


The Bt toxins engineered into GM Bt crops are not specific to target pests and close relatives but can negatively affect a range of non-target organisms, including beneficial insects that help protect crops, beneficial soil organisms, and mammals.


  1. Marvier M, McCreedy C, Regetz J, Kareiva P. A meta-analysis of effects of Bt cotton and maize on nontarget invertebrates. Science. 2007;316:1475-7. doi:10.1126/science.1139208.
  2. Losey JE, Rayor LS, Carter ME. Transgenic pollen harms monarch larvae. Nature. 1999;399:214. doi:10.1038/20338.
  3. Jesse LCH, Obrycki JJ. Field deposition of Bt transgenic corn pollen: Lethal effects on the monarch butterfly. J Oecologia. 2000;125:241–248.
  4. Lang A, Vojtech E. The effects of pollen consumption of transgenic Bt maize on the common swallowtail, Papilio machaon L. (Lepidoptera, Papilionidae). Basic Appl Ecol. 2006;7:296–306.
  5. Schmidt JE, Braun CU, Whitehouse LP, Hilbeck A. Effects of activated Bt transgene products (Cry1Ab, Cry3Bb) on immature stages of the ladybird Adalia bipunctata in laboratory ecotoxicity testing. Arch Env Contam Toxicol. 2009;56(2):221-8. doi:10.1007/s00244-008-9191-9.
  6. Hilbeck A, McMillan JM, Meier M, Humbel A, Schlaepfer-Miller J, Trtikova M. A controversy re-visited: Is the coccinellid Adalia bipunctata adversely affected by Bt toxins? Environ Sci Eur. 2012;24(10). doi:10.1186/2190-4715-24-10.
  7. Hilbeck A, Moar WJ, Pusztai-Carey M, Filippini A, Bigler F. Prey-mediated effects of Cry1Ab toxin and protoxin and Cry2A protoxin on the predator Chrysoperla carnea. Entomol Exp Appl. 1999;91:305–316.
  8. Lövei GL, Arpaia S. The impact of transgenic plants on natural enemies: A critical review of laboratory studies. Entomol Exp Appl. 2005;114:1–14. doi:10.1111/j.0013-8703.2005.00235.x.
  9. Ramirez-Romero R, Desneux N, Decourtye A, Chaffiol A, Pham-Delègue MH. Does Cry1Ab protein affect learning performances of the honey bee Apis mellifera L. (Hymenoptera, Apidae)? Ecotoxicol Environ Saf. 2008;70:327–333.
  10. De Vendomois JS, Roullier F, Cellier D, Séralini GE. A comparison of the effects of three GM corn varieties on mammalian health. Int J Biol Sci. 2009;5:706–26.
  11. Gab-Alla AA, El-Shamei ZS, Shatta AA, Moussa EA, Rayan AM. Morphological and biochemical changes in male rats fed on genetically modified corn (Ajeeb YG). J Am Sci. 2012;8(9):1117–1123.
  12. El-Shamei ZS, Gab-Alla AA, Shatta AA, Moussa EA, Rayan AM. Histopathological changes in some organs of male rats fed on genetically modified corn (Ajeeb YG). J Am Sci. 2012;8(10):684–696.
  13. Séralini GE, Clair E, Mesnage R, et al. [RETRACTED:] Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize. Food Chem Toxicol. 2012;50:4221-4231.
  14. Séralini GE, Mesnage R, Clair E, Gress S, de Vendômois JS, Cellier D. Genetically modified crops safety assessments: Present limits and possible improvements. Environ Sci Eur. 2011;23. doi:10.1186/2190-4715-23-10.
  15. Castaldini M, Turrini A, Sbrana C, et al. Impact of Bt corn on rhizospheric and soil eubacterial communities and on beneficial mycorrhizal symbiosis in experimental microcosms. Appl Env Microbiol. 2005;71:6719-29. doi:10.1128/AEM.71.11.6719-6729.2005.
  16. Zwahlen C, Hilbeck A, Gugerli P, Nentwig W. Degradation of the Cry1Ab protein within transgenic Bacillus thuringiensis corn tissue in the field. Mol Ecol. 2003;12:765-75.
  17. Cheeke TE, Pace BA, Rosenstiel TN, Cruzan MB. The influence of fertilizer level and spore density on arbuscular mycorrhizal colonization of transgenic Bt 11 maize (Zea mays) in experimental microcosms. FEMS Microbiol Ecol. 2011;75:304-12. doi:10.1111/j.1574-6941.2010.01013.x.
  18. Cheeke TE, Rosenstiel TN, Cruzan MB. Evidence of reduced arbuscular mycorrhizal fungal colonization in multiple lines of Bt maize. Am J Bot. 2012;99:700–707. doi:10.3732/ajb.1100529.
  19. Tank JL, Rosi-Marshall EJ, Royer TV, et al. Occurrence of maize detritus and a transgenic insecticidal protein (Cry1Ab) within the stream network of an agricultural landscape. PNAS. 2010. doi:10.1073/pnas.1006925107.
  20. Rosi-Marshall EJ, Tank JL, Royer TV, et al. Toxins in transgenic crop byproducts may affect headwater stream ecosystems. Proc Natl Acad Sci USA. 2007;104:16204-8. doi:10.1073/pnas.0707177104.
  21. Bøhn T, Traavik T, Primicerio R. Demographic responses of Daphnia magna fed transgenic Bt-maize. Ecotoxicology. 2010;19:419-30. doi:10.1007/s10646-009-0427-x.