The effect of GM crops on local insect life


Blogging on Peer-Reviewed ResearchA large study weighs up the existing evidence on the impact of GM crops on local insect life, providing some much-needed scientific rigour to the GM debate.

In Europe, the 'GM debate' about the merits and dangers of genetically-modified (GM) crops is a particularly heated one. There is a sense of unease about the power of modern genetic technology, and a gut feeling that scientists are 'playing God'. These discontents are stoked by the anti-GM camp, who describe GM crops with laden and fear-mongering bits of unspeak like 'Frankenstein foods' and 'unnatural'.

Bt cotton is better for non-targeted insects than non-resistant crops sprayed with insecticdes.In a debate so fuelled by emotion and personal values, scientific research and a critical analysis of the evidence rarely gets a look-in. But science has to grudgingly admit some blame in this, because there is actually precious little research on the safety of GM crops. And many of the studies that have been done were short-term and poorly replicated.

A lack of research is dangerous. It provides opening for people on either side of the debate to quote single, small studies as canon and brushing aside any research that contrasts with their stances.

Michelle Marvier and colleagues from Santa Clara University, California, are trying to change all that. They have analysed over 42 field experiments on GM crops to get an overall picture about their safety. The technique they used is called meta-analysis, a statistical tool that asks "What does everyone think?" It works on the basis that individual small studies may be far from conclusive, but pooling their results together can lead to stronger and more accurate results.

Some GM crops are resistant to specific insect pests.They looked at three strains of GM-crops that had been modified with genes from a soil-dwelling bacterium called Bacillus thuringiensis. The transferred genes are responsible for producing a number of biological (and therefore 'natural') insecticides. When moving them across to plants, geneticists typically try to match the insecticide to the pest they are trying to fight. (In the image on the right, Bt-peanut leaves are protected from the damaging European corn borer)

The toxins are delivered at high dosages to pests, but are restricted to the plant (and sometimes even to particular tissues). They can also be added to the chloroplast genome, which is quite separate form the plant's nuclear DNA. This stops them from being transferred to other plants.

The hope is that these so-called 'Bt crops' can help to minimise the collateral damage of less targeted insecticide sprays. In theory, only pest insects that eat valued crops are killed, while the rest of the ecosystem is unharmed.

That's what Marvier set out to test. She looked at field experiments which tested the impact of caterpillar-resistant cotton and maize plants on the abundance of other groups of insects and invertebrates.

She found that these other creatures are found in greater numbers in fields containing the caterpillar-resistant GM plants, compared to those sprayed with conventional insecticides. However, the GM crops also led to slightly lower numbers of non-targeted insects compared to fields where no GM crops and no insecticides were used.

The results stayed the same even when Marvier analysed them in more detail. For example, she found much the same thing when she only looked at experiments that had been published in peer-reviewed scientific journals.

So assuming that Bt crops do indeed reduce the use of insecticides (and that's far from proven), then they will also, as claimed, reduce the collateral damage caused by these chemicals. But they're not as good for the environment as using no insecticides at all, be they engineered or sprayed.

Bt-crops are better than large-scale insecticide spraying.At the local level, Marvier's study provides some much-needed scientific backbone to the GM debate. But the real decisions need to be weighed up at a larger level. For example, it's all well and good to say that a no-insecticide, no-GM field is the best solution, but that leaves farmers in a bit of a lurch.

One of the big criticism levelled against organic farming is that it leads to lower yield than other practices and requires more agricultural land to be viable and that deals a bad hand to farmers in the developing world. This in turn could lead to deforestation and habitat loss.

On the other hand, Marvier advises caution when interpreting her work. This study has revealed just one benefit of GM crops and even then, only for one specific type of genetic modification. Many of the studies involved isolated patches of land, rather than entire farming systems, where the situation is more subtle. Not all non-GM crops are sprayed with insecticides, while not all GM crops are free from them.

Any benefits must also be weighed against potential health or environmental risks, and again, these must be researched carefully.

To Marvier, the clearest message from her study is that we have started to accumulate enough data to look at this issue from an empirical, evidence-based point of view. If we are to make sound decisions, there is little room for anecdotal evidence or knee-jerk responses guided by personal philosophy.

For example, there is a certain irony to the opposition to Bt crops. Because its insecticides are 'natural', the bacterium is one of the few pesticides that organic farmers are allowed to spray onto their crops.

The bacteria of course use the exact same genes that are transplanted into Bt-engineered crops. Some may argue that this method is better because it is more 'natural', because the genes stay within the organism they were intended for. But is that really better?

Wholesale Bt spraying is a crude technique than the specific and targeted use of Bt-engineered crops. It means that the surrounding land is also covered in the bacteria and creatures other than pests are exposed to its entire gamut of toxins. And because farmers need constant supplies of the bacteria, it soaks up more money.

Reference: Marvier, McCreedy, Regetz & Kareiva. 2007. A meta-analysis of effects of Bt cotton and maize on nontarget invertebrates. Science 316: 1475-1477.

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But science has to grudgingly admit some blame in this, because there is actually precious little research on the safety of GM crops.

I'm curious to know what you would consider more than "precious little research". My impression is that there is a lot of research on this. The problems are that large scale filed studies are difficult, for all sorts of reasons, and that it is not clear how studies on the effects of one transgene generalize to others.

"The effect of GM crops on local insect life"

This is a misleading headline, and several parts of the post were similarly imprecise. Studying the effects of plants that have been modified to include Bacillus thuringiensis genes is fine and good - and for the reasons that you mentioned - but it does not tell reveal anything about how 'genetically modified plants affect local insect life'. It only reveal how some Bt-modified plants affect local insect life, under certain conditions.

There are many many many many different ways that plants could be modified to be more productive or more reliably productive, and each of those modifications will have different effects on insects, just as choosing to switch from growing corn to growing potatoes will affect the local insect life. Please be careful to not reflexively lump 'all genetic modifications' into a single category, and particularly please do not do so in a way that implies all genetically modified plants will have the same effects.

By oscar zoalaster (not verified) on 19 Apr 2009 #permalink

Ed, your story seems infected with the GM apologists' biases. Sure, Bt toxins in the bacteria are the same as those engineered into the plants, but the actual Bt wash off, so people aren't exposed to substantial amounts of it. Second, the large amount of it concentrated in the plants creates a strong selection pressure, so the insects will quickly become resistant to it. GMers can waltz along to another insecticide, but organic farmers will be stuck. That's an excellent result for Monsanto, but not so good for the rest of us.

By Nathan Myers (not verified) on 19 Apr 2009 #permalink

These are fair points all. This post is 2 years old, and I'll bear your comments in mind if I write about this topic again. As always, the feedback is appreciated.


Thank you for writing a sensible post on genetic engineering. I am molecular plant physiologist who is currently investigating metabolic "unintended side effects" of transgene insertion and am continually frustrated by the wall of noise on genetic engineering coming from non-scientists and sociologists who have no concept of the nuts and bolts of plant breeding or agronomy.

It's not hard to imagine a transgenic crop that would be unsafe (e.g. potatoes engineered to produce the alkaloid solanine), but the vague "dangers" of genetic engineering usually posited by opponents generally already occur in normal plant breeding or are unavoidable consequences of having 6 billion mouths to feed. For one thing, our elite wheat lines were exposed to heavy doses of ionizing radiation back in the '50's to generate additional genetic diversity. This rearranged the genome in a MUCH more dramatic and unpredictable way then letting agrobacterium randomly insert DNA (which it does in cultivated walnut, grape and cane berries routinely anyway) - and no one has suffered from eating bread for the past 3 generations.

Suggesting that organic farming can solve our agricultural problems is kinda like saying bicycles can save our transportation problems. Bicycles are romantic and aesthetically pleasing to rich Westerners, but old problems can only be fixed with NEW solutions.

I highly recommend the following:
Divergent perspectives on GM food
Nature Biotechnology 20, 1195 - 1196 (2002)


You're wrong in suggesting that endogenous pesticides will create resistance faster than sprayed ones. I could just as easily suggest the opposite since all insects in a field are subjected to traditional sprays, while only those feeding on the crop are subjected to endogenous pesticides. Likewise, just as not finishing your prescribed antibiotics favors resistance of human pathogens, pulses of sprays (versus continuous endogenous ones) could encourage resistance in insects. It also makes no sense to suggest that chemical runoff is a positive byproduct of spraying - that's how ag pollution poisons waterways (e.g. the Gulf of Mexico dead zone).

Your whole argument is moot regardless because insect and pathogens ALWAYS evolve resistance to pesticides, organic or otherwise (except for extreme biocides like sulfur and copper (both of which are "organic" and the former of which causes the most farm worker injuries in California). Bt (and Roundup) are incredible safe to humans and break down quickly in the environment. Industrialized countries have incredibly strong regulations assuring that no meaningful chemical residue exists on your food.

Before you bad mouth these incredibly safe(er) and green(er) technologies, you should look into the chemicals they are replacing (e.g. atrazine).

Plant pathologists and entomologists know that most plants are already resistant to most pathogens and insects largely thanks to their huge arsenals of toxins they already contain (many of which are advertised to health nuts as "phytochemicals").

The future of genetic engineering will be the filling in of these few susceptibility gaps with thoughtful, highly government-regulated transgenes.

What you should REALLY be worrying about it the fact that in a few years, hobbyists will be able to genetically modify organisms in their basement as easily as they now write computer software.

Matt: yes that is the main worry. Not just hobbyists. Not all scientists are governed by ethics committees. In many places, high tech research goes on without "ethics-review" or whatever the term is. So the fear is that someone will let loose a GM crop that can do some huge damage....

"If we are to make sound decisions, there is little room for anecdotal evidence or knee-jerk responses guided by personal philosophy."

Words to live by.

As someone who grew up on a cotton farm in Australia during the period of bangs over from tradditionally bred varieties to gm bolguard and inguard (roundup ready and bt moified) I find it hard to believe there is any question about whether gm crops reduce the number of sprays. In bad seasons before gm cotton was introduced, it was not uncommon foe. Field to be sprayed 8+ times over the growing season. Now, even in the worst of times, when insect pressures are at their greatest, it is relatively rare to use even 1 spray.
A significant decrease and I find it hard to believe no one has produced papers showing this to be the case.

Congratulations, Ed, you've hit the Big Time. You're getting what the professional propagandists call "placements".

In any politically-charged area, particularly where one side has lots of money to spend, it's easy to create useful bias just by arranging to choose which questions get studied. Perhaps the truth will come out eventually, but too often too late to do any good.

By Nathan Myers (not verified) on 20 Apr 2009 #permalink

Maybe you could tell us the truth Nathan, and back your assertions up?

I have to say, the anti-GM lobby is it's own worst enemy. Their arguments show they haven't the slightest clue what they are talking about.

By Marc Abian (not verified) on 20 Apr 2009 #permalink

My superficial impression is that GM plants that are Roundup Ready result in more sprayings, not fewer. If true, the takeaway from this study is to not make broad pronouncements about GM being generally safe or generally unsafe.

Brian Schmidt, Roundup Ready crops will get more Roundup, but you have to consider that if they were not getting Roundup they would have to be sprayed with several other herbicides to control the various different kinds of weeds. Roundup ready results in fewer total sprayings, of only one sort of herbicide.

In regard to the topic of the original post, I would be interested to see the effects of GM crops on insect populations in subsequent years after the GM crop was harvested. Do populations rebound quickly or remain low for a time? Also interesting is if there is a long term change in which species are more or less common in GM fields.