Bt crops

The International Service for the Acquisition of Agri-Biotech Applications (ISAAA) does what its name says it will do. Among other things, it promotes genetically modified (GM, genetically engineered, GE) crops. On the other side of this heated debate, GM Watch tells us what’s wrong with GM.

I propose ISAAA for the World’s Worst Acronym Award (WWAA 😉 ) but it’s a good source of information about GM crops. So is GM Watch. It’s worth looking at both of these contrasting points of view regarding the GM crops called Bt crops. These are the crops engineered to make Bt toxin, which kills insects. A common soil bacterium called Bacillus thuringiensis makes a protein which turns into Bt toxin when insects eat it.

Organic farmers sometimes spray B. thuringiensis as a pesticide. This isn’t the same as planting Bt crops. You could scroll down the GM Watch homepage to see how Susan Pusztai explains. Organic farmers can choose to spray ‘a preparation of weakened or most often dead bacteria… only in the case of high insect infestation and only onto the affected area.’ Dr Pusztai says that this spraying puts no active toxin onto the land or onto the crops. Whereas in a Bt crop, active toxin appears in every tissue and every cell, all the time.

So a Bt crop puts far more selective pressure on the pests, to evolve resistance, than the Bt bacterium would do. That’s behind the reports of Bt-resistant ‘superbugs’, which I blog about under my ‘evolution’ tag.

Also, says Dr Pusztai, when people or livestock eat Bt crops we’re eating active Bt toxin. It’s a lectin, a protein that we don’t easily digest and that binds to carbohydrates including those in cell walls. Bt toxin might do that in our gut. That’s behind some of the reports of GM as a health hazard.

Bt toxin isn’t just one protein. ISAAA tells us, ‘there are more than 200 types of Bt proteins identified with varying degrees of toxicity to some insects.’ Does that mean some Bt toxins are more likely to be health hazards than others? To us, to livestock, to wild mammals, birds and insects? Or are they all bad news? That’s relevant to debate about whether a new Bt maize called 1507 should be allowed in Europe.

Some people think Bt crops are great. You can scroll down the ISAAA article to see a list of countries where Bt crops were being grown commercially by 2004.

Ferris Jabr of Scientific American says it’s a good idea to ‘farm a toxin’ by growing Bt crops. His focus in that article is on the aubergine (eggplant, brinjal, Solanum melongena) which is a staple food in several Asian countries. As my fellow blogger applpy at Thought + Food told us a few months ago, Bt brinjal is now grown in Bangladesh but not in India.

Mr Jabr tells us how universities and biotech companies, including Mahyco which is part-owned by Monsanto, made Bt brinjal. He says, ‘When properly managed, Bt crops increase yields and make croplands far friendlier for insect populations as a whole by reducing the use of broad-spectrum chemical insecticides that kill indiscriminately. Fewer chemical sprays also translate to cleaner grains, legumes and vegetables mixed into processed foods and sold whole in the produce aisle.’

‘Properly managed.’ Can we expect proper management of Bt crops?

Mr Jabr continues, ‘Bt crops are not entirely benign, however, nor are they a panacea. Despite the unparalleled specificity of Bt toxins, recent studies indicate that in a few rare cases they may inadvertently kill butterflies, ladybugs and other harmless or helpful insects, although so far there is no solid evidence that they poison bees. Even more concerning, agricultural pests can, will and have become resistant to Bt crops, just as they inevitably develop immunity to any form of pest control.’

I’ll give the final word today to my fellow blogger jsneal at Living With Insects. He tells us the good and the bad about Bt crops.


About argylesock

I wrote a PhD about veterinary parasitology so that's the starting point for this blog. But I'm now branching out into other areas of biology and into popular science writing. I'll write here about science that happens in landscapes, particularly farmland, and about science involving interspecific interactions. Datasets and statistics get my attention. Exactly where this blog will lead? That's a journey that I'm on and I hope you'll come with me.
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10 Responses to Bt crops

  1. Pingback: A GM potato for Europe? | Science on the Land

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