Health

Ten Reasons why farmers should think twice before growing GE crops
E. Ann Clark, Plant Agriculture,
University of Guelph(
eaclark@.uoguelph.ca)
www.plant.uoguelph.ca/faculty/eclark

The tide appears to be turning against GE crops, but if what you read in the farm press is any indication, farmers will be the last ones to know it. The future of agricultural biotechnology is in serious jeopardy, as consumers, grain buyers, processors, and supermarket chains line up around the world refusing to buy GE products.The Deutsch Bank, largest bank in Europe, has gone public with its concerns, advising thousands of institutional investors across the world to sell GE. And so they have, affecting not just stock prices but encouraging major life science companies to consider spinning off their GE divisions - if anyone will buy them. Don't believe it?

Have a look at a revealing report entitled Ag Biotech: Thanks, But No Thanks? http://www.biotech-info.net/Deutsche.html) which was published in July 1999 by the Deutsche Bank, the largest bank in Europe. They stated that "Thirty days ago, the investment community accorded only positive attributes...to GMO corn and soybean...Today, the term GMO has become a liability. We predict that GMOs, once perceived as the driver of the bull case for this sector will now be perceived as a pariah." This highly influential report was sent to thousands of the world's largest institutional investors. It concluded by down-rating Pioneer Hi-Bred from HOLD to SELL, coupled with a broad negative recommendation for the seed sector in general (specifically, for Monsanto, Delta & Pine Land, Novartis, and to a lesser extent, Dow).

Toward a partial remedy to the sparse coverage of alternative viewpoints in the farm press, my goal today is to give you some of the agronomic reasons why farmers should think twice about growing genetically engineered crops. Do you really need what they offer in the first place? For example, Are European cornborers (Ostrinia nubilalis (Hubner) sufficiently predictable on your farm as to justify the extra expense of growing Bt hybrids as insurance? In Ontario, Sears and Schaafsma (1998) reported that infestations had to be high enough to cut yields by at least 5-8 bu/ac before Bt-corn was economically competitive. They further noted that conventionally-bred cornborer-resistant hybrids performed as well as Bt-hybrids under low-to-moderate cornborer infestations. Thus, unless cornborer infestation is high and predictable, you may have other, less costly, options to control cornborer, besides Bt-corn.


Transgenic solutions come with a price tag that is high, both in terms of dollars and in indirect costs (see below). Whether Bt or herbicide-resistance, be sure you can justify it economically before trying it out.

2. How much of a yield loss can you experience and still make enough money to justify growing GE crops? And keep in mind, that if cornborer risk is high enough to justify using a Bt hybrid, then you'll also need to factor in yield loss on the 20% or more of unsprayed"refugia" set-aside that you are expected to plant to a non-Bt hybrid - without insecticidal protection.. Contrary to what has been promised, GE crops often do not yield more and not infrequently yield less than the best available conventionally bred cultivars and hybrids.

Why? Because not all genetic backgrounds within a given crop will tolerate a transgene(1), and those that will are not necessarily the highest yielding ones. Further, there is a metabolic cost to expressing herbicide-resistance or the Bt-endotoxin. So, if you were expecting a yield gain - as promised, if we are going to "feed the world" - then you may well have been disappointed. And the fault was not necessarily yours, no matter what they told you. An April 99 review of 40 soybean varietal trials in the northcentral region of the US by Oplinger et al. (1999) found a mean 4% yield drag in RR soybeans. In July 99, Benbrook (1999) reviewed 8200 university-based yield trials for the 1998 season, and reported a mean yield loss of 4.6 bu/ac or 6.7% compared to the top conventional varieties (or 3.1 bu/ac or 5.3% relative to all tested varieties)(Benbrook, 1999). In Iowa, Duffy (1999) surveyed Iowa grain producers and reported an average RR-soybean yield reduction of 2 bu/ac (4%) over 365 fields in the 1998 season In Ontario, the most recent available data (for 1998) show a 1-3% mean yield drag in RR soybeans (Table 2) relative to the trial mean (n=57) - not to the highest yielding cultivars. However, soybean breeders advise that the yield gap is closing as RR genes are moved progressively into higher and higher yielding cultivars. Nonetheless, there is a cost to the crop from expressing the genes for Roundup resistance, and it manifests itself in lower yields.

In Wisconsin, Lauer and Wedberg (1999) compared yield of Bt-corn and standard corn hybrids in 1995 and 1996 over four site-years of planting. At each site-year, both groups of corn hybrids were subjected to either natural levels of cornborer infestation (with no insecticide) or were exposed to artificially high levels with four intentional inoculations. At natural levels of infestation, non-Bt corn yielded the same as Bt-corn, namely, 158 bu/ac. Artificially elevated levels of ECB reduced yield of non-Bt hybrids by 8%, to 146 bu/ac but had no effect on Bt-hybrid yields - 158 bu/ac. At least for early Bt hybrid introductions, there was no yield advantage to Bt-corn except at high levels of infestation. This situation was expected to change as Bt genes were entered into breeding programs of more elite materials.

3. When are they going to get it right? The evolution of pest resistance to Bt is a foregone conclusion, as virtually everybody will admit. Pesticidal plants like Bt-corn are no different than DDT or atrazine - insects and diseases, and to a lesser extent weeds, are extremely well adapted to evolve resistance whenever faced with a powerful and efficient "screen" -like tens of millions of hectares of cropland all expressing the same toxin. The only source of contention among scientists is "when" and how to delay resistance. The high dose/refugia model which has been widely promoted by both industry and government proponents was supposed to be the best available strategy to forestall resistance. However, you may have noticed that the size of the recommended set-aside has increased just about every year. When Bt hybrids first came out, producers were told to hold back a 5% refugia (to plant to a non-Bt hybrid). Then it was 10%, and now it is most commonly recommended as 20% (plan submitted to the US EPA by Monsanto, Mycogen, Dow Agrosciences, Novartis, and Pioneer Hi-Bred; AgNews, 23 Apr 99; also by the Bt Corn Coalition to the Plant Biotechnology Office of the CFIA in October 1998), although some are calling for 40%. Why the confusion? Why is the figure changing - and always upwards? The confusion is caused because those promoting refugia as the best solution have not done their homework. "None of the essential assumptions of the high dose/refugia strategy have been verified for BT corn", according to Andow and Hutchison (1998) in a chapter on Bt resistance in Now or Never, edited by Mellon and Rissler. This is a clear example of a general and pervasive problem with agricultural biotechnology - namely,technology has preceded science. Ag biotech has been released prematurely, for reasons of profit, before sufficient scientific evidence has been developed to produce an effective and reliable product. And unfortunately for proponents of this model, many of these untested assumptions have now been challenged by recent research published in the most prestigious journals. What we now know is that the high dose/refugia model is unlikely to work, at least for cornborer.So, where does that leave you?

4. Do the GE crops, in fact, do what is promised? Reduce production costs? Reduce pesticide applications? Increase yield? Increase profit? Costs and profits are a hard issue to address in the abstract, as much varies with weed and insect pest pressure and other farm-specific issues. Duffy and Miller (1999) of Iowa State University interviewed 800 Iowa farmers to determine if growing GE crops was in fact more profitable in 1998. Based on 62 continuous corn fields, 315 rotated corn fields, and 365 soybean fields: Duffy and Miller (1999) concluded that the difference in profitability was so small as to be non-significant for both crops. They stated "Use of (GMO) seed didn't appear to impact a farmer's bottom line for either corn or soybean production, but the reasons were different. In soybeans, GMO yields were lower but so were costs. In corn, yields and costs were higher when GMO seed was used....profitability does not appear to be a decisive factor". Thus, claims of higher profitability for GE crops were not borne out by this producer survey. Virtually all independent (not industry-funded) evidence suggests that yield is lower - not higher - in GE soybeans, although claims of higher yield potential in Bt corn do appear to be valid (Duffy, 1999). But what about insecticide use? If you use Bt, then you don't need to use insecticides, right? And that protects both you and the environment, and that's good, right?

1 Major resistance genes must be very rare In diamond back moth, one of eight species that have already evolved resistance to Bt, Tabashnik et al. (1997) showed that resistance is not rare - its actually 10X higher than the highest previous estimate

2. Resistance genes must be nearly recessiveAccording to Huang et al. (1999), resistance in ECB is dominant, while in other pest lepidopteran species, resistance varies from recessive to incompletely dominant. Furthermore, resistance varies not only among species, but also among types of Bt endotoxins, e.g. CryIAc, CryIAb, CryIIA

3. Non-Bt refuges must provide susceptible pests to mate with resistant ones; requires random mating and suitable dispersal distancesCornborers consuming Bt (and living) typically suffer delayed development, which causes them to reach reproductive maturity out of phase with their neighbors in the refugia. They won't be able to mate anyway. The same thing has been confirmed most recently in pink bollworms on cotton (Liu et al.,1999)

GE was $4/acmore than non-GE. Indeed, Monsanto made just such a claim in a press release dated 21 May 99, in response to recent research showing an adverse effect of Bt pollen on Monarch butterflies (see below). Monsanto stated: "In 1998 use of Bt insect-protected corn reduced or eliminated the use of broad spectrum chemical insecticides on some 15 million acres of US farmland". Now, that would be a pretty impressive achievement, if it were true. So, let's see - some 71.4 million acres of corn were grown in the US in 1998, and data from the USDA National Agricultural Statistics Service (http://www.usda.gov/nass/pubs/rptscal.htm , courtesy Chuck Benbrook,personal communication) shows · First, only a tiny fraction of corn acreage is treated with insecticides at all

· Second, most insecticides are used for rootworms and soil insects, not European cornborer (ECB, the target of Bt-corn). Thus, based on the known target organism of the applied insecticides (Table 4), at best Bt-corn could have reduced insecticide usage on 1-2% of the acreage sown to corn in 1998 in the US - e.g. 0.7 to 1.4 million acres not the 15 million acres trumpeted by Monsanto). ·

And finally, given that the purpose of the Monsanto claim was to debunk the notion that Bt pollen affected Monarch butterflies more than insecticides, note that the rootworm/soil insect insecticides are applied at planting - well before Monarch butterflies could possibly be at risk. Note also the Duffy and Miller (1999) survey of Iowa corn producers, showing a modest increase (not decrease) in the cost of insecticide per acre, although Bt-corn growers treated only 12% of their acres compared to 18% for non-Bt-corn growers.

So, if GE crops either reduce yield without affecting profit (RR-soybeans), or have a neutral to positive effect on yield without affecting profit (Bt-corn), and don't reduce risks of insecticide use - just who is it that benefits from growing GE crops?!

5. How will genetic pollution from your own fields and from your neighbors' fields, compromise your ability to control weeds on your own land? The term "genetic pollution" refers to the fact that pollen moves - sometimes great distances. And when transgenic pollen moves, it carries with it transgenic traits - like herbicide resistance. Pollen of canola can move 8 km, while that of both corn and potato can move about 1 km. Gary Stringam, a professor at the University of Alberta has found that canola could outcross and produce 5-6% contaminated plants up to 400 m from the original source (MacArthur, 1998b). A recent study in the UK found pollen from GE-canola contaminating bee hives up to 4.5 km from the source field. All of this makes it difficult to imagine how Monsanto and others can hold onto their precious genes - or for you as a farmer to avoid genetic pollution of unwanted genes - either moving to your fields from your neighbors, or to your neighbors fields from your land.

Consider the case of Tony Huethers, who farms near Sexsmith, Alberta. In 1997, he planted two fields, separated by 30 m, to canola. On the west side, he planted Quest, a Roundup (glyphosate)-resistant cultivar, while on the east side, he planted 20 acres of Innovator, a Liberty (glufosinate)-resistant cultivar, and the rest of his 140 ac field to 45A71, a cultivar that is resistant to Pursuit (imazethapyr, an ALS inhibitor) and Odyssey. In spring of 1998, two applications of Roundup to the east field - the one sown in 97 to Innovator and 45A71 - killed all his weeds, except for a healthy population of blooming canola! It was apparently, and predictably, Roundup resistant canola, and was thickest near the road.The biotech manager for Monsanto in Saskatoon - Aaron Mitchell - said "We always expected a level of natural outcross would occur within the species", and that the source was likely native pollinators. He stated that the potential for cross pollination was already well known to seed companies and researchers, and that "farmers need to talk to their neighbors about the canola they grow"(MacArthur, 1998a).

6. Will genetic pollution expose you to lawsuits or other legal actions by neighbors, analogous to spray drift? Did you hear the one about Percy(2), or the $147,000 order of Terra Prima organic tortilla chips that were rejected and had to be destroyed due to cross-pollination by Bt corn, or the non-GE seed corn that was found - after sale - to have been inadvertently pollinated by GE pollen? Pollen moves, reportedly up to 8 km for a crop like canola. Nothing new about that. But until now, no one minded if alleles for higher yield or improved rust resistance moved on pollen from neighboring fields into their own. It is only since the advent of GE that pollen movement has come to be known as genetic pollution, because the traits that move can be deleterious. Herbicide resistant volunteer canola can be a real drag the following year. But worse than that, what is your recourse if your non-GE crop is contaminated by GE pollen and you were aiming for a GE-free market? With GE crops selling at a discount because major clients don't want to buy them, genetic pollution poses a clear risk to every farmer, not just organic farmers. Consider a 26 August 99 letter from Consolidated Grain and Barge Company (of Indiana; 812 838-4017) to its producers: "Segregating 'non GMO' grains on farm will pay dividends this year....testing standards and tolerance levels will be very tight and any contamination, no matter how trivial it may seem, will lead to a positive test and will be rejected for 'non GMO' premiums....".

And just where would you turn to recover the profit lost due to some stray Bt pollen? An article in the UK Farming News (18 June 99) notes that farmers are increasingly unwilling to grow GMO trials on their farms, specifically because of fears of legal damage claims from neighbors.

One underwriting manager, Sid Gibson, reportedly advised that "The big unknown is where there is a risk of cross-contamination. Farmers considering growing GM crops should get their legal advisers to look at the contract very carefully. Responsibility should be with the biotech company or institution carrying out the trials." Our cousins across the pond are taking a forthright look at the legal implications of potential genetic pollution from GE crops - why aren't we?

7. Will the livestock eat it? The refusal of European and perhaps Japanese consumers to accept GE foods has led some farmers to assume the GE grain can still be fed to livestock. But can it? Over a year ago, a letter in the March 98 issue of the Farmers Weekly (UK) reported that producers in Nebraska and Iowa were having trouble getting livestock to graze Bt-cornfields. A farm specialist from Dawson County, Nebraska said "At first we thought it was a joke, but I have heard it enough now that we are looking into what could be going on." Now, over a year later, comes an article by Sprinkel (1999) reporting case after case in the midwest where: · cattle refused to graze Bt-corn stubble, · hogs went off feed when GE grains were included in the ration, · cattle stopped eating when switched to GE silage · rate of gain dropped when switched to GE feed, and · cattle broke through a fence and walked through RR-corn to mow down a non-GE hybrid, leaving the RR-corn untouched.So much for substantial equivalence. Livestock appear to know the difference between GE- and non-GE-feedstuffs, even if government regulators don't. So now what are we going to do with all that GE grain?

8. What about the bugs? The balance of nature is more than just a teaching tool for grade school students. It is reality - even in today's highly artificial agricultural environment. It has been said that the only really effective control of insects is that provided by nature, by the competition, predation, and parasitism of one organism on another. Just as killing off the wolves unleashes deer populations and allows them to skyrocket beyond the carrying capacity of their environment, so too our efforts at pest control can often have unintended side effects on other insects or microbes. Unlike the original Bt microbes, in which the Bt endotoxin exists in a harmless proto-toxin form until ingested by the target organism, GE-Bt plants synthesize active endotoxin in every cell. Inserting Bt genes into plants eliminates two of the three levels of screening that formerly made Bt highly selective for particular pests. Thus, the potential for harm to non-target organisms appears to be much higher in Bt crops than with foliar applied Bt. One example of an adverse effect of Bt radiating out into the wider environmental community has been reported from Switzerland and Scotland. One of the insects which normally feeds on cornborer is a beneficial called the green lacewing, which favors soft-bodied insects such as cornborer and aphids. Unfortunately, green lacewings were also harmed (killed or suffer delayed development) by Bt, whether they ate it directly or after eating cornborers which had been reared on Bt corn. The same thing happened with ladybugs eating aphids which had been raised on transgenic (snowdrop lectin) potatoes. So - the adverse effect of these plant pesticides affects not just the target organism but beneficials, such as ladybugs and green lacewings too. And of course, this could have additional effects on natural pest control for other crop and garden pests.This is just one example of the adverse environmental effects of field crop GE, which was missed entirely by the remarkably weak "environmental risk assessment" process employed by both the US and Canada to facilitate entry of GE crops into commerce.

9. Is it safe to eat GE foodstuffs? The government says so, but is that enough? Consider what professionals working in the field have to say:

a. On 17 May 99, the mainstream British Medical Association, representing 115,000 doctors, published a statement calling for an open-ended moratorium on the planting of GM crops, a ban on releasing GMOs into the environment, and a review of the World Trade Agreement to ensure that human health and safety take precedence over global trade in foodstuffs and seed (Frith and Murphy, 1999). Their specific concerns included the use of antibiotic resistant marker genes, which were regarded as posing a slight but "completely unacceptable risk" of enhancing drug-resistant bacteria. Their general call was for much greater scientific certainty about risks of GMOs.

b. Transgenes move readily across species barriers between wholly unrelated organisms via what is called "horizontal gene transfer". Movement of transgenes from GE plants into soil microbes has already been documented (Hoffmann et al., 1994). Transgenic DNA can also survive long enough in the gut to transfer genes into intestinal microflora (MacKenzie. 1999). Because almost all commercial GE crops are bred using antibiotic resistance genes as a marker (this is unrelated to the agricultural use, just part of the breeding process), this means that consuming GE foodstuffs can allow genes for antibiotic resistance to move into the E. coli and other microbes that are naturally present in your stomach, or that of your child.Plasmids, which are a special kind of vector commonly used to insert transgenes into chromosomes, have also been tracked not just in the stomach of rats, but across the intestinal wall and integrated into the DNA of rat intestinal, spleen, and liver cells (Doerfler and Schubbert, 1998; Schubbert et al., 1997). Even more alarming, these same plasmids have been followed across the placental barrier and into the DNA of embryonic rats in utero (Schubbert et al., 1998).

Do we actually know enough to be able to state with confidence that the food is safe? Are we asking the right questions? And what if we are wrong? It has been said that the risks posed by GE organisms exceed those from nuclear reactors - specifically because GE organisms are alive, can mutate, and can transmit and recombine their transgenes into the DNA of unrelated organisms, with wholly unpredictable consequences. Consider the stakes - is it worth it?

10. Who is going to buy your GE grain this fall? Next fall? Segregation to enable both export and labelling appear to be a foregone conclusion, despite heroic efforts to convince people and nations that it was both impossible and unnecessary. But it is not just consumer who want labelling. Concern is growing among farmers. In June 1999, Elbert van Donkersgoed of the Christian Farmers Federation of Ontario, questioned the use of some kinds of biotechnology on the farm. While noting the potentials, he emphasized also the risks, even going so far as to state that "disaster is possible". And just a few weeks ago, the CFFO broke ranks with other mainstream farm organizations by passing resolutions calling for, among other things, labelling of GMO-foodstuffs - to give consumers the choice.

The American Corn Growers Association has gone so far as to caution their members about growing GE crops next year, principally because of market uncertainties, but expressing concerns about agronomic issues as well.

In their July 99 report, the Deutsche Bank highlighted the potential development of a two-tiered marketing system, with the premium going to non-GE crops - that's right, just the opposite of industry projections. And pretty good crystal ball gazing it was, as just a few months later,premiums of US$0.08-0.15/bu for non-GE corn and US$0.20-0.30/bu for non-GE soybean are reportedly already on offer in the US. Indeed, European buyers are reportedly already looking to off-shore sites, namely Brazil, and even domestic European soybean production to ensure a supply of non-GE soybeans.

Canadian canola growers lost $30 million in export sales to Europe in 1998 alone, because consumers refused to accept GE canola oil. Japan is not far behind. The biggest potential losers are US farmers, who have so fully accepted the promise of GE technology as to plant a third of the corn crop and half of the soy and cotton crops to GE cultivars and hybrids.In short, demand for GMO grain and products, or livestock produced from GMO grains, is rapidly drying up. The high-handed behavior of the US, Canada, Australia, and three South American nations in refusing to sign the Biosafety Protocol at Cartagena, Colombia last winter and in Europe just this past month is beginning to look short-sighted. As acknowledged even by Glickman, Secretary of Agriculture in the US, you cannot force people to eat something they don't want to eat.

Conclusions

So, when deciding whether or not to grow GE crops next year, I'd encourage you to consider:

1. Do you really need what they offer, and is GE the best way to deal with it, given the likelihood of higher costs and lower yields?

2. Be very aware of insurance/liability risks from neighboring farmers (for genetic pollution), environmentalists (for Monarch butterflies and other issues), and consumers (for food safety).

3. Don't assume that because it is in the marketplace, that it is "safe", has been tested for "environmental risk (a la Monarch butterflies), or is necessarily in your best interests. Government is not asking the right questions. Trade interests are taking precedence over the interests of producers, consumers, or the environment. The world doesn't want our grain.Don't get caught in the middle.

4. Industry proponents often state proudly that twenty years of intensive research ensure the safety and effectiveness of field crop GE. If that is so, one can only wonder how they missed all these critical problems now being uncovered by independent (not industry funded) scientists almost every week. Twenty years, nay 1000 years of research would be useless in safeguarding either the environment or human health if the objective is "how to make it work" instead of "what happens when it does", or even better "why are we doing this in the first place". And that, in truth, is why we are where we are today. The financial viability of commercial producers is ill-served by those who persist in denying the substance of consumer concerns - and hence the marketability of GE crops - around the world.

References

  • Andow and Hutchison. 1998. Bt resistance. In: M. Mellon and J. Rissler (ed) Now or Never. Consumers Union.
  • Benbrook, C. 1999. Evidence of the magnitude and consequences of the Roundup Ready soybean yield drag from university-based varietal trials in 1998. Ag BioTech Info Net Technical Paper No. 1 (http://www.biotech-info.net/herbicide-tolerance.html#soy)
  • Doerfler, W. and R. Schubbert. 1998. Uptake of foreign DNA from the environment: the gastrointestinal tract and the placenta as portals of entry. Wiener Klinische Wochenschrift. 110/2:40-44.
  • Duffy, M.and L. Miller. 1999. 1998 Crop survey shows equal returns for GMO, non-GMO crops. http://www.leopold.iastate.edu/9-22-99gmorel.html
  • Frith, M. And E. Murphy. 1999. BMA Calls for ban on GM crops and food. PA News 17 May 99
  • Hoffmann, T., C. Golz, and O. Schieder. 1994. Foreign DNA sequences are received by a wild-type strain of Aspergillus niger after co-culture with transgenic higher plants. Curr. Genetics 27:70-76.
  • Huang, F., L.L. Buschman, R.A. Higgins, and W.H. McGaughey. 1999. Inheritance of resistance to Bacillus thuringiensis toxin (Dipel ES) in the european corn borer. Science 284:965-967.
  • Lauer, J. and J. Wedberg. 1999. Grain yield of initial Bt corn hybrid introductions to farmers in the northern corn belt. J. Prod. Agric. 12:373-376.
  • Liu, Y-B, B.E. Tabashnik, T.J. Dennehy, A.L. Patin, and A.C. Bartlett. 1999. Development time and resistance to Bt crops. Nature 400:519.
  • MacArthur, M. 1998a. Canola crossbreeds create tough weed problem. Western Producer, 15 October 98.
  • MacArthur, M. 1998b. Resistant canola expected. Western Producer, 15 October 98.
  • MacKenzie, D. 1999. Can we really stomach GM foods? New Scientist (30 January 99)
  • Oplinger, E.S., M.J. Martinka, and K.A. Schmitz. 1999. Performance of transgenetic soybeans - Northern US. Presented to the ASTA Meetings, Chicago.
  • Schubbert, R., D. Renz, B. Schmitz, and W. Doerfler. 1997. Foreign (M13) DNA ingested by mice reaches peripheral leucocytes, spleen, and liver via the intestinal wall mucosa and can be covalently linked to mouse DNA. Proc. Nat. Acad. Sci.94:961-966 (February 1997)
  • Schubbert, R., U. Hohlweg, D. Renz, and W. Doerfler. 1998. On the fate of orally ingested foreign DNA in mice: chromosal association and placental transmission to the fetus. Mol. Gen. Genet. 259:569-576.
  • Sears, M. and A. Schaafsma. 1998. Responsible deployment of Bt corn technology in Ontario. http://www.cfia-acia.agr.ca/english/plant/pbo/btweb2_e.html
  • Sprinkel, S. 1999. When the corn hits the fan. Acres, USA Special Report 18 September 1999.
  • Tabashnik, B.E., Y-B Liu, N. Finson, L. Masoson, and D.G. Heckel. 1997. One gene in diamondback moth confers resistance to four Bacillus thuringiensis toxins. Proc. National Acad. Sciences 94:1640-1644.

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