Transgenic corn’s resistance to pests has benefited even non-transgenic corn

Genetically modified crop resistance to pests benefits non-modified crop, U of Minnesota study finds

Areawide suppression dramatically reduced the estimated $1 billion in annual losses caused by European corn borer

Transgenic corn’s resistance to pests has benefited even non-transgenic corn, a new study led by scientists from the University of Minnesota shows.

The study, published in the Oct. 8 edition of the journal Science, found that widespread planting of genetically modified Bt corn throughout the Upper Midwest has suppressed populations of the European corn borer, historically one of corn’s primary pests. This areawide suppression has dramatically reduced the estimated $1 billion in annual losses caused by the European corn borer, even on non-genetically modified corn. Bt corn, introduced in 1996, is so named because it has been bred to produce a toxin from the soil bacterium Bacillus thuringiensis (Bt) that kills insect pests.

Corn borer moths cannot distinguish between Bt and non-Bt corn, so females lay eggs in both kinds of fields, said the study’s chief author, University of Minnesota entomology professor William Hutchison. Once eggs hatch in Bt corn, young borer larvae feed and die within 24 to 48 hours. Because it is effective at controlling corn borers and other pests, Bt corn has been adopted on about 63 percent of all U.S. corn acres. As a result, corn borer numbers have also declined in neighboring non-Bt fields by 28 percent to 73 percent in Minnesota, Illinois and Wisconsin, depending on historical pest abundance and level of Bt-corn adoption. The study also documents similar declines of the pest in Iowa and Nebraska. This is the first study to show a direct association between Bt corn use and an areawide reduction in corn borer abundance.

Economic benefits of this areawide pest suppression have totaled $6.9 billion over the past 14 years for the 5-state region. Surprisingly, non-Bt corn acres accounted for $4.3 billion (62 percent of this total benefit.) The primary benefit of Bt corn is reduced yield losses, and Bt acres received this benefit after the growers paid Bt corn technology fees. But as a result of areawide pest suppression, non-Bt acres also experienced yield savings without the cost of Bt technology fees, and thus received more than half of the benefits from growing Bt corn in the region.

Paul Mitchell, an agricultural economist at the University of Wisconsin-Madison, and a co-author of the study, emphasized that “previous cost-benefit analyses focused directly on transgenic crop acres. This study is the first to include the value of areawide pest suppression and the subsequent benefits to growers of non-transgenic crops. In this case, the value of the indirect yield benefits for non-Bt corn acres exceeded the net value of direct benefits to the Bt corn acres.” The authors note that their analysis does not consider benefits for other important Midwestern crops affected by European corn borer, such as sweet corn, potatoes and green beans. Hutchison observed however, “that additional environmental benefits from corn borer suppression are likely occurring, such as less insecticide use, but these benefits have yet to be documented.”
The authors were able to document the suppression of European corn borer in Minnesota, Illinois and Wisconsin because state entomologists have monitored pest populations for more than 45 years in those states. Pest suppression and similar benefits to adopters and non-adopters alike may be occurring as a result of the widespread use of transgenic insect-resistant crops in other parts of the United States and the world, but those benefits cannot be documented without adequate data.

Finally, the authors emphasize that sustaining the economic and environmental benefits of Bt corn and other transgenic crops for adopters and non-adopters alike depends on the continued stewardship of these technologies. Farmers, industry, and regulators need to remain committed to planting non-Bt corn refuges to minimize the risk that corn borers will develop resistance to Bt corn. The Science magazine study shows that Bt corn is more valuable to society than originally realized, which makes maintaining its effectiveness even more important.

Contact: Patty Mattern
University of Minnesota
Press release

See BBC Item:
8 October 2010 Last updated at 08:06 GMT Share this pageFacebookTwitterShareEmailPrint
GM crops bring cash harvest to non-GM varieties
By Richard Black
Environment correspondent, BBC News

Insect pest control by genetically-modified crops can raise yields and profits from non-GM varieties grown nearby, a study from the US indicates.

Researchers looked at maize grown in five US states, where plants are affected by the European corn borer.

They found fewer borers – and higher profits – in GM fields, and in neighbouring non-GM fields.

Writing in the journal Science, they say this is the first time that a wider impact on profits has been shown… contd at link.

and also

Suppression of Cotton Bollworm in Multiple Crops in China in Areas with Bt Toxin–Containing Cotton
Kong-Ming Wu, Yan-Hui Lu, Hong-Qiang Feng, Yu-Ying Jiang, Jian-Zhou Zhao*
Transgenic cotton that has been engineered to produce insecticidal toxins from Bacillus thuringiensis (Bt) and so to resist the pest cotton bollworm (Helicoverpa armigera) has been widely planted in Asia. Analysis of the population dynamics of H. armigera from 1992 to 2007 in China indicated that a marked decrease in regional outbreaks of this pest in multiple crops was associated with the planting of Bt cotton. The study area included six provinces in northern China with an annual total of 3 million hectares of cotton and 22 million hectares of other crops (corn, peanuts, soybeans, and vegetables) grown by more than 10 million resource-poor farmers. Our data suggest that Bt cotton not only controls H. armigera on transgenic cotton designed to resist this pest but also may reduce its presence on other host crops and may decrease the need for insecticide sprays in general.

Science 19 September 2008:
Vol. 321. no. 5896, pp. 1676 – 1678
DOI: 10.1126/science.1160550

David Tribe is an applied geneticist, teaching graduate/undergrad courses in food science, food safety, biotechnology and microbiology at the University of Melbourne.

  • Eric Baumholder

    This result merely confirms what many have been claiming for a long time. Similar effects have been documented with Bt cotton and cotton bollworms.

    An interesting variation on this situation is said to occur when a normal farmer has a neighboring organic farm. Organic farms are reservoirs for weeds, pests and diseases, which prompt higher-than-usual applications of chemical sprays for adjacent conventional farms.

    There is said to be a reciprocal effect, however; organic farms benefit from the weed, pest and disease control measures used by surrounding conventional farms.

    Given the political climate, these reciprocal effects will likely never be studied.

    • pdiff

      n interesting variation on this situation is said to occur when a normal farmer has a neighboring organic farm. Organic farms are reservoirs for weeds, pests and diseases, which prompt higher-than-usual applications of chemical sprays for adjacent conventional farms.

      Do you have definitive evidence of this?

  • Ewan R

    I feel the paper may overestimate the differences in a certain respect (I can’t quite put it into words right now, but I’ll attempt and hopefully a competant wordsmith or statistician (I’m looking at you pdiff) can either make me look silly or pat me on the head and say well done) – the paper estimates benefits to Bt growers by doing the following:-

    Direct benefits for Bt maize
    growerswere calculated as the value of the yield gain
    for Bt maize relative to non-Bt maize, minus the
    additional cost for Bt maize seed

    However this seems kinda unfair as the non-Bt maize is actually protected by the Bt maize but has its benefits calculated by estimating the damage had populations been at historic average levels rather than non-existant (practically) – I think it would have been a fairer comparison to assume the Bt maize either was, or wasn’t there for the Bt growers – essentially assuming the same damage rather than comparing to the non-GM yields in the same area – as such I’d guess that bt growers probably come out marginally ahead on a per unit area level.

    Although this would also increase the overall economic benefits, so either way you look at the data it paints Bt in a rather spiffy light

  • pdiff

    “(I can’t quite put it into words right now, but I’ll attempt and hopefully a competant wordsmith or statistician (I’m looking at you pdiff)”

    Ha! I’m a statistician, not an economist!! :-) You may have a point, although I think their rationale was to standardize the responses, especially for comparisons across states. The non-GM maize is acting as your “wasn’t there for bt-growers” values. How else would you get those?

    More troublesome for me is their rate modeling (detailed in the supplement) which essentially assumes that rate, given by ln(Nt/Nt-1) is a function of Nt-1, that is, the rate response is computed based on the number of larvae at time t-1 (Nt-1). This is then regressed against Nt-1. Anyone else see the circular logic there :-) This can be done with appropriate time series or diff EQ methodology, although I don’t see that they did this. But then, economists do this sort of thing all the time. It’s black-boxy kind of stuff.

  • Ewan R

    The non-GM maize is acting as your “wasn’t there for bt-growers” values. How else would you get those?

    I would have thought it would be fairer to assume the same baseline in terms of income for both the bt and non-bt growers (maybe the paper did this and I misread, 3 hours sleep != good) – if they can work this out for the non-GM growers then shurely the same can be done for the GM growers with practically no extra effort.

    I probably shouldn’t try and quibble over how a paper published in science did things even with enough sleep however.

    • pdiff

      I’m not sure I’m following you (and I had a good sleep) :-) It may be implied in the computation, e.g. the differential effect of Bt is measured relative to non-Bt. That would assume baselines are comparable. Maybe more problematic is they adjust Bt growers for the extra cost of GM tech, but seem to assume that non-Bt assumes no additional control costs.

      • Ewan R

        I may just be reading the article wrong.

        To me it appears they’re using different comparisons.

        a) They appear (to me, based on fuzzy thinking) to be comparing Bt yields with non-Bt yields in the same year (ie bt yields with yields of corn sans Bt, but protected by nearby Bt) – which would be a good way to look at the economic benefit of Bt compared to non-Bt if that’s as far as it went.

        b) However they then appear to compare non-Bt to predicted yields should there be no protection from Bt at all.

        They then conclude that b) is greater than a) which I don’t think is a fair comparison.

        I need to reread this when I’ve had some sleep I think (or someone here can just smack me upside the head and tell me I’m reading it wrong…) – probably sometime around summer 2011

  • Anastasia Bodnar

    I love that we can depend on you guys to be critical of every paper, no matter the subject, whether it supports or goes against genetic engineering. It’s truly wonderful to be among fellow critical thinkers and skeptics! 😀

    Ewan, Science Mag is not above criticism by any means.

    • Ewan R

      I wouldnt hold science above criticism, just above my criticism today, I think!

      Also note that my criticism results in Bt looking awesome either way.

      I know who signs my pay check!

  • Eric Baumholder

    It’s remarkable that these findings should be subject to intense doubt.

    Long-term regional suppression of pink bollworm by Bacillus thuringiensis cotton. Proceedings of the National Academy of Sciences, published online before print February 5, 2003, doi: 10.1073/pnas.0436708100 Available at:

    Note to pdiff: You asked, “Do you have definitive evidence of this?”

    But I’d already said, “Given the political climate, these reciprocal effects will likely never be studied.”

    • Ewan R

      It’s remarkable that these findings should be subject to intense doubt.

      All findings should be subject to intense doubt!

      Although my doubt here is not as to whether there was an effect (I’d be surprised if there wasn’t – I recall reading a farming blog in the past year where the idea that dropping Bt from your rotation would make sound economic sense so long as most people around you didn’t do the same thing) but as to whether the difference in economic return is quite what the paper is stating it to be (although given that it only looks at corn, and not other crops which the corn borer effects, it may well be that the economic impact on non-Bt users is significantly higher than stated)

      I’m also left wondering how many people in the business side of Monsanto are desperately trying to figure out how to capture a percentage of the value.

    • pdiff

      It’s remarkable that these findings should be subject to intense doubt.

      Not “intense doubt” on my part, just interested and cautioned inspection. But your comment makes me ask why? What’s the main weapon used by GM proponents against anti-GM studies? The “studies” they cite are designed and carried out poorly. You should be no less critical of GM supporting studies lest the weapon be turned on you. If you’re going to make an argument, then make it well.

      What’s more, we only have data here that is highly suggestive. They show a correspondence between GM tech introduction and an overall suppression of certain pests. Basically, two data points, counting your soybean article. Are you going to sit back and take that as conclusive? Granted, these results are intriguing, but they are not conclusive. Do we know that GM is the causative factor here? No. Do we know the mechanisms involved? No. Do we have multiple lines of evidence for this? No. These are simply two pieces of an overall larger argument.

      Note to pdiff: You asked, “Do you have definitive evidence of this?”

      But I’d already said, “Given the political climate, these reciprocal effects will likely never be studied.”

      Ummm, if we consider GM to be “conventional” ag, then I think this article, as well as the one you cited above, generally qualify , although admittedly, they don’t specifically look at organic farms. Your “political climate” remark reminds me of creationists whining that Intelligent Design will never be correctly examined because those “Evilutionists” won’t let the scientists do it (and it fails for the same reasons).

      I’ll take your statement to mean that you suspect it hasn’t been researched, but don’t actually know.

  • Eric Baumholder

    Ewan, Pdiff,

    The same regional effect has been noticed in China. Suppression of Cotton Bollworm in Multiple Crops in China in Areas with Bt Toxin–Containing Cotton. Wu KM et al (2008). Science, Vol. 321. no. 5896, pp. 1676 – 1678.

    There is a very handy adage regarding scientific claims, closely related to Occam’s Razor, which states that extraordinary claims demand extraordinary evidence. Applying that to this latest finding = ‘so, who’s surprised?’

    And it’s actually true that reciprocal effects between organic and conventional fields are widely discussed, but not studied. Ok, that invites proof of a negative, but that’s the way things fall. And there actually needs to be a good reason for an intriguing notion not to be studied. It’s widely known that saying anything less than flattering about organic agriculture is like poking a hornet’s nest with a stick.

    • Ewan R

      Eric – to reiterate I’m totally unsurprised that there’d be a decrease in pest levels in non-GM corn as a result of mass adoption of GM corn (kinda mirrors vaccination really, only the herd is static and field shaped rather than all over the place and vertebrate shaped) just questioning whether or not the economic benefits for non-adopters (particularly when adoption is more than 50%) is really greater than the economic benefit for adopters – I categorically expect that both parties will have reaped benefits – and if anything my way of looking at it (assuming it is different to how the paper looked at it, which I’m not altogether sure of, based on sleep deprivation I’m avoiding looking at the paper again until I’m slightly more aware and awake – if sensible I’d probably avoid the topic altogether and get some sleep, but nobody ever accused me of being sensible without being soundly thrashed with a halibut) would retain the benefits for non-adopters and increase the benefits for adopters making Bt more of a net economic boon than if my concerns are unfounded.

      On the China thing – I’m not sure that’s the only paper that looks into that – I need to dig out another if I can find it (brain fog strikes – I’ll see what I can do some day I sleep more than 3 hours)

    • pdiff

      Eric, there seems to be much debate about nothing here. This is a good line of investigation and is obviously being looked at, however, the hypothesis here is GM Bt tech is the causal agent suppressing overall pest levels. We have 3-4 surveys that show some supporting evidence for this, but they are only that – supporting evidence. As I mentioned before, a better argument will need multiple lines of evidence. For example, so far we are just talking about non-GM here, not, as we have been implying, organic. Non-GM’rs may well be spraying nasty ol’ chems, just like the old days. If so, is the decline due to overall lower pest numbers, or has the pest demography changed to give more susceptible pests in non-GM cases (Note that much of the survey data comes only from non-GM fields. Researchers in many cases “assumed” pest levels in GM fields would be zero, so they were not sampled). The case would be much stronger if one could show an actual mechanism(s) for the observed change. Some way to tie it back directly to GM.

      Perhaps little research on the negative effects of organic is done because a) it isn’t a problem. Very little of western ag is actually organic, and b) with GM, non treated areas are not necessarily viewed as bad. Non GM buffers, for example, are mandated for many GM’s to reduce resistance development. Organic operations would fall into that category.

  • Karl Haro von Mogel

    I was wondering what everyone thought about some of the other implications of this paper. For example, the Union of Concerned Scientists’ report, Failure to Yield, compared yields of non-Bt corn to Bt corn, and concluded that there was a 3-4% yield gain from the Bt genes. But if this new study holds true, then non-Bt corn has been bounced up by about that much in yield, and it would seem, therefore, that the actual yield gain of Bt corn is higher than 3-4%. Although it would be mathematically crude to simply add percentages instead of bring up the calculator to multiply them, if the high number of Bt acres planted gave the non-Bt crops a 3% yield gain (let’s say), and the Bt crops have a 3-4% yield gain over that, would that mean that Bt’s actual yield effect is 6% or so? I suppose it would depend upon the source data for yield gain, but there’s something missing from these calculations.
    Next, let’s consider the issue of pesticide use. Charles Benbrook tried to compare pesticide use in GE fields versus non-GE fields, and claimed a large increase in herbicide use (in crude pounds per acre) due to GE crops. Although I disagree with his simplistic subtraction of nasty pesticide pounds from not-so-nasty herbicide pounds calculation, this new paper also has implications for his paper. If the use of Bt corn has through this overall farm ecological effect reduced the insecticides sprayed per acre on non-Bt conventional corn, then this means that the actual reduction in insecticide sprays due to Bt is much bigger than he is reporting. This would mean that you cannot just compare the non-GE corn to GE Bt corn and find the difference, because the sprays on non-GE corn have been reduced by the effect of the Bt corn.
    What do y’all think? Are there other comparisons and issues related to this discussion that this new research would deepen our understanding of?

  • David Tribe

    That’s an interesting angle Karl.

    If there is protection of surrounding crops, does that mean greanhouse tests have to be designed and interpreted carefully, or if done in isolation, underestimate the value of Bt?

  • Charles M. Rader

    I haven’t seen any formal study, but I think the experience of papaya growers on the island of Puna in Hawaii is analogous. The ringspot virus was destroying the papaya industry. Now, most of the papaya plants on the island are GMO varieties with virus resistance. Since there are so many “vaccinated” papaya, the reservoir of potential infections is reduced and the non-GMO papaya derive some protection.

  • Andre

    There is a similar protective effect in vine-growing, and I have seen claims that organic or biodynamic vine-growing wouldn’t exist without that protective effect from conventionally managed vineyards. (Conversely, there are higher risks for conventionally managed vineyards from organic vineyeards in which the pest management strategy has failed, but this risk is minimised in the case of GM cops). .

    I also like the Margaret Mellon comment in the press that by her estimates, the savings ran to only about 3% of the total value of the corn crop in the five states. How much are those 3% when related to the farmer’s profit?

    • Karl Haro von Mogel

      Well, Failure to Yield did call 3-4% yield gain “insignificant” – so I can see how 3% is not cause for celebration on the part of the UCS. So is 6% significant, now?

      I think that lots of people would appreciate a 3% raise – and for farmers it is going to be more than that because costs have not increased with it, making this 3% of gross a larger proportion of the net income.

      What popped into my mind just now was that people in favor of GE crops are sometimes called ‘reductionistic’ as an insult to mean that they aren’t taking into account other factors beyond the major ones. Now it appears that the shoe is on the other foot, and that critics of GE crops in the case of the effects of Bt are not taking into account the ecosystem effects of Bt corn on non-Bt corn farmers. They’re being ‘too reductionistic’! :)

      I am already seeing this study being spun into the claim that “non-GMO farmers profit more – so don’t grow GMOs!” But if every farmer in this prisoner’s dilemma defects and grows the non-GE corn again, everyone loses.

  • Eric Baumholder

    Charles, Andre,

    I keep hearing these claims about reciprocal benefits/burdens between conventional and organic. Do either of you have a cite to share on that? The claims have been made so often that they have some ‘truthiness’, but meanwhile I personally would like something substantial to hang my hat on.

    • Karl Haro von Mogel

      Yes, some refs would be nice. I’m very interested in “spillover” effects of the actions of one farmer versus another. Just like pesticides can drift from one farm to another, and GE pollen can flow, it makes sense that weed seeds and insect pests can also do the same. But what is the actual effect?
      “Nuisance” (in the legal sense) has been used to describe GE pollen flow, but would that also apply to pest pressures from a nearby farm?
      My next door neighbor had some big thistles in the corner of their backyard, and soon enough, there were thistle seeds all over my yard, including in my compost bin.

    • pdiff

      Eric: ” ….but meanwhile I personally would like something substantial to hang my hat on.”

      :-) Me too!

      Karl:“My next door neighbor had some big thistles in the corner of their backyard, and soon enough, there were thistle seeds all over my yard, including in my compost bin.”

      This is a gnarly beast to pin down. The outcome depends on who ends up with the better lawyer. You complain about the weeds. They counter that their “natural” lawn is less disruptive than your artificial grass. You point out that the thistle is an invasive alien species. They come back that so are your honeybees and, BTW, they are benefiting from the thistle flowers. And so on, etc, etc.

      The argument in Ag is no different. It ends up being a matter of who can convince the judge/jury/public that the other side is doing more damage (physical or economic).

  • Andre

    Bingo for Papaya, although it is a narrative, but here the issue is/was binary:
    Dennis Gonsalvesn, “Transgenic Papaya in Hawaii and Beyond”

    Farmers quickly planted the transgenic papaya seeds, which were nearly all ‘Rainbow’ because the farmers in Puna favored this transgenic cultivar. Harvesting of ‘Rainbow’ started in 1999 (Figure 5), and grower, packer, and consumer acceptance were widespread. The papaya industry had been spared from disaster. Table 1 shows the impact of the transgenic papaya on stemming the destruction caused by PRSV. Since 1992, when the virus was discovered in Puna, the yearly amount of fresh papaya sold from Puna had gone from 53 millions pounds in 1992 to 26 million pounds in 1998. In 2001, Puna papaya production rebounded to 46 million pounds of fresh market papaya. Another important impact has been the dramatic reduction of PRSV inocula in Puna, because infected fields have been replaced by the resistant transgenic papaya, and because many abandoned infected fields have since been destroyed. These conditions, along with judicious isolation and rouging of infected plants, have enabled growers to continue to produce nontransgenic papaya, especially to supply the Japan market, which does not yet allow the importation of transgenic papaya. In January 2003, Canada allowed the importation of transgenic papaya. Yet another benefit is that papaya acreage has expanded on Oahu due to the use of PRSV-resistant transgenic ‘Rainbow’ (or new hybrids that have been derived from ‘Rainbow’).

    For vine, internet searches are hopeless because you get thousands of hits from organic/biodynamic vinegrowers and their aficionados.

  • Eric Baumholder

    Charles, Andre, Karl,

    You may find the following to be interesting — fines for organic farmers who fail to spray for voracious insects.

    Organic farmers miss out on locust spray. Business Spectator (Australia), August 31, 2010. Available at:

    [excerpt from archived text]

    Locusts that emerged in plague proportions in spring last year have laid eggs in pastures across northern Victoria, and there are fears it may result in the worst plague in 75 years this spring.

    “The Premier is arrogantly threatening that farmers will be prosecuted if they don’t spray locust hatchings, but many organic producers are finding that they can only access spray that will, in effect, destroy their farm’s accreditation and their livelihoods.”

    • Charles M. Rader

      I have to admit, that bothers me. By analogy, can my neighbor demand that I keep dandelions out of my lawn?

      • Karl Haro von Mogel

        Yeah, obviously, you can be unreasonable to demand that typical, expected home practices such as having dandelion plants be prohibited because of the potential for seeds to spill over into your lawn and sprout. But if I grew some crazy invasive weed en masse that was ravaging my neighbors’ yards, you can bet that I shouldn’t be allowed to do it, as it is not a typical, expected practice that they should reasonably be able to expect me to do, and it would be considered a “nuisance.”

        How about transgenics? Weed & pest loads? How typical or expected is it for a farmer to grow a GE crop, or another farmer to have a field margin that is just crazy with weeds? What is interesting is that the idea of classifying pollen flow from genetically engineered crops as a nuisance is and has been tried. But in order to try to do it legally, GE opponents have been drafting their bills to specifically exclude the argument that because a huge proportion of farmers are growing them, that it would mean it is an expected or typical practice in agriculture. Think about that for a moment. Currently 93% of farmers (by acreage) who grow soybeans in the US grow GE soy – and some lawyers are trying to argue that this 93% of acres does not count as “expected” or “typical.” Think about something that over 90% of homeowners do, and imagine a bill being drafted to declare that a public nuisance, of course, on the 7% of homeowners that don’t do it. Pet ownership? Car ownership? Actually living in the house and the noises that that typically entails? Clearly, these are not being drafted with the interests of everyone in mind, but instead a very narrow group.

        Politics is like a busy intersection – everyone wants to drive through it straight, turn right, left, and perhaps U-turn as well, which means that everyone has to have a chance. If one of the two streets was a huge through-way with a lot of traffic, and the other was a minor side street, it would be wrong for the majority to decide that the side street doesn’t get any green lights so that they can move the most traffic possible through the intersection. And conversely, the side street has no right to stop the major through-way more than is reasonable to get some cars through from their direction.
        It seems like with this intersection as an analogy – some people want to declare the major through-way a nuisance to the side street. And that’s a nuisance. :)

  • David Tribe

    Yes that got a fair bit of publicity here in Victoria. The organickers do have one option, spraying with a fungus Metarhizium (spelling might be wrong). It’s a modern biotechnology they have not demonised, and involves release of live pathogen microbe to kill locusts, but as its not a GMO, they avoid worrying about the potential downsides.

  • Ewan R

    Somewhat more awake now, looking at the supplemental data supplied I still think my original observations hold water and that the economic benefit to Bt growers has been grossly underestimated in the paper (notwithstanding reduction in chemical sprays)

    The net benefit ($/ha) for Bt growers is
    the Bt yield minus the non-Bt yield, this quantity multiplied by the maize price, and then the
    additional cost for Bt maize seed subtracted (table S5).

    Real figures vs real figures.


    Annual state average yields for this counterfactual scenario that Bt maize had not been
    commercialized (Ynon-Bt) are calculated as Yno Bt = (1− E[λ ])YBt for each year, where the Bt yield
    each year is the same as used to calculate benefits for Bt growers (table S5). The yield gain for
    non-Bt growers due to the suppression of O. nubilalis is the non-Bt yield calculated for each state
    based on the actual observed state average larval density (Ynon-Bt) minus the yield based on the
    larval density under the counterfactual case that Bt maize had never been commercialized (Yno Bt).
    This gain multiplied by the maize price is the benefit ($/ha) for non-Bt growers due to O. nubilalis
    suppression. Multiplying this benefit by the total planted area (ha) gives the annual total net
    benefit ($). Annual values are adjusted for inflation to a base year of 2009 using the Consumer
    Price Index (S25).

    in my opinion a fairer comparison would be to compare real bt and non-bt yields to the counterfactual data – bt farmers obviously also enjoy the economic benefit of corn borer supression (compared to the baseline of non-utilization, not compared to the baseline of yields sans Bt in areas with Bt growing) but this isn’t taken in to account in the calculations looking at the economic benfits to Bt farmers.

    This of course would make no impact whatsoever on the absolute benefit to non-utilizers, but would, I think, increase it such that it no longer appears that non-utilizers benefit more (which I think is false – we’re not discussing complete eradication of the borer, in which case you would expect non-utilizers to benefit more as they pay no tech fee – there’s a significant reduction in borer levels but as this doesnt hit zero there remains a yield benefit for adoption of bt (albeit small – 0.1 – 0.4 Mg/Ha in 2009 which equates to ~$14 – $58 /Ha which is still a profit (tech fee /Ha is $5-$11)

    • Ewan R

      Keeping in mind the paper refers to Bt (obvious) non-Bt (corn yields etc when Bt is present in the state but not on that farm) and no-Bt (which refers to the counterfactual situation in which no-Bt was grown)

    • pdiff

      “in my opinion a fairer comparison would be to compare real bt and non- bt yields to the counterfactual data – bt farmers obviously also enjoy the economic benefit of corn borer supression. “

      Yes, I see what you are saying here, but they assumed that Bt is 100% effective, and hence, Bt growers do not receive any benefits from suppression. It would work whether there were lots of them or not. That’s probably not true in reality, but it seems to be the position of the authors.

      ” … we’re not discussing complete eradication of the borer, in which case you would expect non-utilizers to benefit more as they pay no tech fee “

      They pay no tech fee, but may, in fact, have other control costs. They are simply non-Bt growers, not necessarily organic growers.

      A related question: Are GM growers utilizing non-GM buffer zones or trap crops allowed or required to apply other control measures in those areas?

  • Ewan R

    Yes, I see what you are saying here, but they assumed that Bt is 100% effective, and hence, Bt growers do not receive any benefits from suppression.

    If Bt is 100% effective then they should still compare the yield with Bt to the yield if Bt had never existed. The gain in yield you obtain from Bt isn’t just that which is over and above what you’d get without it, but that which is over and above that which you’d get if it wasn’t utilized by anyone (if it isn’t then the non-Bt comparison with non-utilization is a complete moot point and the paper is meaningless) – particularly as if you dropped the use of Bt you’d move from the Bt to non-Bt group, which if you look at the comparisons used should mean you’d increase your income (which you wouldn’t)

    • Eric Baumholder

      There’s another confounding factor which needs to be considered.

      Bt corn has substantial benefits even when corn borer populations are low. This is because insect damage at any level makes the crop much more susceptible to drought stress.

      So, in a sense, Bt maize is drought-resistant. Not as a primary trait, but as a secondary, but measurable, effect.

      What this means in practice is that Bt crops will outperform whatever benefits may accrue to neighbors, whenever there is any insect pressure whatsoever.

      Of course, this will have to be balanced against the cost of seed, which is lately in a state of disruption, to put things mildly.

  • pdiff

    Now you see why I’m not fond of economics. :-) Too much guesswork determining benefits and harmful effects, what baselines should be used, and, literally, what the price of corn is/was in Michigan.

    You’re completely right, Eric. There may be many unmeasured secondary effects, both positive and negative, that are hard, if not impossible, to measure. Which is why caution should be used with surveys like this. We need a good testable models here to explain the how and why this would happen.