Bt insecticide risks in the agricultural landscape

April 2017

As the biotech industry and regulators cling to the notion that 'Bt' insecticide is toxic only to the target pests and is easily digested by mammals just like any other protein, science is throwing a few flies in their ointment.

GM crop plants have been created which generate one or several artificial versions of 'Bt' insecticides. These proteins, in their natural forms, are produced by soil bacteria, Bacillus thuringiensis.

It's disturbing to read in a recent scientific paper that:
"Bt toxins can be transferred via the food web and accumulate in organisms to different degrees".

Aware that the lack of public acceptance of Bt-containing GM rice is partly fuelled by concerns over ecological risks, a team of Chinese scientists took a closer look at what could happen to common plant-feeders and their predators in the field.

They put sap-sucking brown plant hoppers on Bt rice for 15 days, and then fed the flies to wolf spiders, a dominant predator which plays a crucial role in South China rice ecosystems. Chemical analysis found Bt protein in the spiders. Observation of the spiderlings found growth tended to be delayed. Gene expression profiling of the spiderlings found 136 genes had significantly altered expression linked to the presence of Bt rice in their food chain. The affected genes regulated the formation of the outer skeleton which spiderlings have to moult and reform in order to grow: this has clear implications for growth rate. Other affected genes are involved in the formation of amino-acids (the building blocks of proteins) with multiple implications.


Under these stress-free experimental conditions, the spiderlings were able to recover from the observed growth disturbance.

Other similar studies of gene expression in wolf spiders, however, have noted multiple responses to stresses to which the animals might be exposed at the same time, such as, pesticides and temperature extremes. A huge variety of artificial Bt proteins is entering the agricultural landscape with no consistent (i.e. predictable) effects on non-target herbivores, nor the carnivores which eat them, nor the microbial communities on which all wildlife health ultimately depends. How benign these humanly-designed Bt toxins are in real-life situations of multiple stresses (from which recovery might be problematic) hasn't been studied.

Blood tests of women and their unborn children in Canada detected the same Bt toxin as the one fed to the brown plant hoppers and wolf spiders in both. Their contamination arose after exposure to a typical Canadian diet. It seems people, including those at the highly toxin-sensitive foetal stage, are accumulating Bt insecticide, just like the wolf spiders.

Children don't of course have to moult in order to grow, but chronic exposure to a food contaminant which disturbs fundamental metabolic pathways such as protein formation, could be permanently damaging. Changes in human gene expression in response to dietary Bt have not been studied.

Up-to-date testing of the the effects of Bt insecticides in the form we are actually eating them is needed NOW.

  • Juan Wang, et al., 2017, Transcriptomic response of wolf spider, Pardosa pseudoannulata, to transgenic rice expressing Bacillus thruingiensis Cry1Ab protein, BMC Biotechnology 17:7
  • Aziz aris and Samuel Leblanc, 2011, Maternal and fetal exposure to pesticides associated to genetically modified foods in Eastern Townships of Quebec, Canada, Reproductive Toxicology 31
  • Dinesh C. Sharma, Toxin from GM crops found in human blood: Study, India Today 11.05.11

    Photo: Rice fields in China. Source Creative Commons

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