5.5 MYTH:

GM Bt crops only affect target pests and their relatives


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

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

5.5.1. Bt crops harm soil organisms

Mycorrhizal fungi benefit plants by colonising 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 colonisation in the roots of 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 colonisation.69 A separate field study on Bt maize residues ploughed into soil after harvest confirmed that Bt toxin resisted breakdown and persisted in soil for months.70

Arbuscular mycorrhizal fungi (AMF) are beneficial fungi that penetrate the root cells of the host plant. Bt maize has been found to decrease arbuscular mycorrhizal fungi (AMF) colonisation of the roots, compared with non-GM maize.71,72

5.5.2. Bt crops harm non-target and beneficial insects

GM Bt insecticide-producing crops have been found to have toxic effects on non-target insect populations,73 including butterflies74,75,76 and beneficial pest predators such as ladybirds77,78 and lacewings.79 Bt crops have more negative than positive impacts on beneficial insects.80 Bt toxin impacts bee learning behaviour, interfering with bees’ ability to find nectar sources for food.81

5.5.3. 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.82 Other studies have found that GM Bt maize biomass is toxic to aquatic83 and soil organisms.69 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.84

5.5.4. Conclusion

Bt crops are not specific to the target pests and close relatives but negatively affect a range of non-target organisms, including beneficial insects that help protect crops.

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