Mendel in the Kitchen A Scientist's View of Genetically Modified Foods (2004) / Chapter Skim
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10 The Butterfly and the Corn Borer
10 The Butterfly and the Corn Borer
Pages 201-222
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From page 201... ...
Victor Davis Hanson is a fifth-generation grape farmer and orchardist in the San Joaquin Valley of California. He is also a professor of classics at California State University.
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From page 202... ...
The decision has already been made by the environmentally correct consumer: He wants fruit plentiful, colorful, hard, and fresh, free from crack and scar -- not high-priced and tasty, overripe, leaking, and pockmarked, a hitchhiking gnat or stowaway fly now swirling amid the glistening produce section at the local supermarket. Under no condition must the vine-hopper's non toxic excrement dot the grape.
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From page 203... ...
In field tests it was found that the toxic Cry proteins worked. The only creatures killed by the poison were the ones that ate the crop -- which is a fair definition of "pest." It is ironic, then, that the fight against genetically modified foods was inflamed by a scientific finding that pollen from Bt corn could, in the laboratory, kill the larvae of a monarch butterfly.
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From page 204... ...
In May 1999, in a one-page letter published in the journal Nature, John Losey and two colleagues in the entomology department of Cornell University told the world that pollen from Bt corn plants kills the larvae of the monarch butterfly. Losey's paper was front-page news in the New York Times; the monarch photo accompanying the story was captioned "Bambi of the insect world." The news traveled around the world, from the BBC to the Boston Globe to the San Francisco Chronicle.
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From page 205... ...
Because of the unknowns -- and the publicity -- a remarkable study was launched. It was funded jointly by a pooled grant provided by the Agricultural Research Service of the USDA and the Agricultural Biotechnology Stewardship Technical Committee (whose members were Aventis CropScience, Dow AgroSciences, E
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From page 206... ...
Still others asked whether monarchs laid more eggs on milkweed plants inside cornfields, where milkweed is a weed, or on plants outside cornfields. Finally, they determined the extent to which egg laying coincided with the week to 10 days during which corn plants shed their pollen.
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From page 207... ...
In other places, particularly in the Midwest Corn Belt, monarchs laid their eggs on milkweed plants inside cornfields just as often as they did on milkweed outside cornfields. The studies also confirmed, as plant breeders had argued, that corn pollen is rather heavy and most of it comes to rest inside the cornfield.
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From page 208... ...
When they combined this assumption with the amount of egg-laying-pollen-shed overlap, the actual pollen densities, and the proportions of milkweed both inside and outside cornfields, they found that about 0.4 percent of the monarch population (or 1 monarch out of every 250) would be at risk of exposure to toxic effects from Bt corn.
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From page 209... ...
In the Midwest, mowing roadsides and using herbicides is probably much more devastating, actually." Anthony Shelton, Losey's colleague in Cornell's entomology department, is equally concerned about the side effects of Bt crops. He does not worry about the monarch: "How many monarchs get killed on the windshield of a car?
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From page 210... ...
The developers of the Lenape potato, in the 1960s, also selected for high toxicity -- without meaning to -- while trying to breed in disease and insect resistance. Again, in the 1980s, trying to reduce the need for chemical insecticides, crop breeders used traditional breeding techniques to create a celery that naturally warded off its pests.
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From page 211... ...
"Sweet corn is sprayed with insecticides frequently, sometimes every two or three days, to ensure that the ears will be attractive at harvest."But while Bt sweet corn has been approved by the EPA, it is not being grown. Instead of replacing the chemical pesticides, Bt field corn has shown farmers the true cost of the damage done by the European corn borer.
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From page 212... ...
As the 2000 report to Congress on the benefits, safety, and oversight of agricultural biotechnology noted, this fact "is often cited by critics of biotechnology as an example of a bioengineered crop that has not met expectations." Rebecca Goldburg of the Environmental Defense Fund, for example, complained to Congress that "Bt corn largely supplements rather than substitutes for insecticide use on field corn." And yet few farmers had expected Bt corn to cut their use of sprays. According to a study by Iowa State University in 1998, 82 percent of the farmers in the Midwest who had planted Bt corn that year said their primary reason for doing so was to prevent losses from the corn borer.
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From page 213... ...
Bacillus thuringiensis differs from another soil bacterium, Bacillus cereus, only in that B thuringiensis contains a plasmid, an extra ring of DNA, that gives it the ability to make toxic Cry proteins, and B
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From page 214... ...
Keeping pests susceptible to Bt, the EPA decided, was "in the public good." "This issue is not new to agriculture," plant pathologist Jim Cook explains."Resistance breeding is an ongoing effort for crops just to stay ahead of the ever-evolving populations of pest species." In The Living Fields, Jack Harlan illustrates this effort to stay ahead in the battle between wheat and the fungus Puccinia, which causes the disease called rust."In North America,"he writes,"we managed to plant a carpet of wheat from northern Mexico well into the prairie provinces of Canada."Although patches of other crops are mixed in, none is large enough to keep the rust spores from traveling on the wind from one wheat field to the next over a total distance of some 2,500 miles. Each year the disease hits first in the south, along the Rio Grande valley.
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From page 215... ...
The costs are particularly high if the new cultivar is a genetically engineered variety, like Bt corn, which must weather extensive safety tests before it can be planted. A four-year life span cannot recoup a company's outlay.
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From page 216... ...
If the offspring received one roundness allele and one wrinkliness allele, the wrinkliness would seem to disappear, masked by the dominant trait. For the larva of a European corn borer in a Bt cornfield, Mendel's experiment means
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From page 217... ...
Shelton chose diamondback moths instead of corn borers for two reasons. First, the diamondback had already shown some resistance to Bt and the trait was known to be recessive.
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From page 218... ...
In order to buy Bt corn seed, farmers must sign grower agreements or stewardship agreements, which "impose binding contractual obligations on the grower to comply with the refuge requirements" -- that is, farmers who plant Bt corn but fail to establish proper insect refuges can be sued. The onus for educating farmers about proper stewardship -- and for ensuring their compliance -- falls on the seed company.
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From page 219... ...
No conventional pesticide has such extensive -- and expensive -- requirements for managing insect resistance, yet as the case of the diamondback moth shows, insects respond to dusts, powders, and sprays by becoming resistant to the pesticide just as they do when eating Bt corn. Leaving the refuge unsprayed means farmers must stand by and watch while pests eat 20 percent or more of their cornfields.
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From page 220... ...
Approving the re-registrations of five varieties of Bt corn in 2001, the EPA noted, "Available data indicate that after six years of commercialization, no reported insect resistance has occurred to the Bt toxins expressed either in Bt potato, Bt corn, or Bt cotton products." If the refugia rules are followed, scientists predict that the corn borer will not evolve to be resistant to Bt corn for at least 99 years. One of Shelton's collaborators, Richard T
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From page 221... ...
Discussing the study with a reporter from Nature Biotechnology News, Tabashnik said, "If I'd gotten up seven years ago and said that there would be no evidence of increased Bt resistance after Bt crops were planted on 62 million hectares" -- meaning the cumulative number of hectares since Bt crops were released in 1996 -- "I would have been hooted off the stage. No one predicted that there wouldn't even be a minor increase, which is extraordinary."
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