By Rachel Massey*
As we saw in REHN #716, genetically engineered crops now planted
in the U.S. and worldwide are mostly designed to tolerate
herbicides or to kill insects or other pests. A small percentage
is designed for other purposes such as resisting infection by
certain viruses. Here we will look at some of the threats
genetically engineered crops pose to ecosystems.
Pesticidal crops may be toxic to nontarget organisms - organisms
they were not designed to kill. For example, BT corn designed to
kill the European corn borer can also be toxic to other closely
related insects, including butterflies and moths.
Monarch butterfly larvae feed on milkweed, which often grows in
or near corn fields. In a laboratory, scientists found that
monarch larvae feeding on milkweed dusted with BT corn pollen
grew more slowly and died at a higher rate than larvae that were
not exposed to the toxic pollen. Another study found these
effects were likely to occur outside the laboratory as well.
Researchers placed potted milkweed plants in fields of BT corn
and measured the number of BT pollen grains that were deposited
on the milkweed leaves. Monarch larvae exposed to BT corn pollen
at these levels had high death rates compared with larvae exposed
to non-engineered corn pollen or placed on milkweed leaves with
The U.S. Environmental Protection Agency (EPA) now expresses
concern about the effects of BT corn pollen on monarchs and other
butterfly species, including the endangered Karner Blue
butterfly. EPA has asked companies to submit data on these
effects, but this "data call-in" occurred four years AFTER EPA
allowed BT corn to be used on U.S. farms.[2,pg.13]
BT corn may also harm the green lacewing, a beneficial insect
that eats agricultural pests. The lacewing may be affected by the
toxin in the digestive systems of insects that have eaten BT corn
but have not been killed by it. This example shows how
non-target effects may interfere with a chain of predator-prey
relationships, disrupting the natural balance that keeps pest
populations under control.
BT crops may also affect non-target organisms by changing soil
chemistry. A 1999 article in NATURE reported that the roots of BT
corn plants released BT toxin into soil. The researchers found
that 90 to 95% of susceptible insect larvae exposed to the
substance released from the roots died after 5 days.
The use of BT crops can also promote the development of
BT-resistant pest populations. As we saw in REHN #716, organic
farmers use BT sprays occasionally as a natural insecticide to
combat severe pest outbreaks. BT crops, in contrast, generally
expose insects to BT toxins day after day, whether or not there
is a major infestation. These conditions increase the likelihood
that BT-resistant insects will evolve. The widespread appearance
of BT-resistant insect pests would mean the loss of one of the
most valuable tools available to organic farmers for dealing with
serious pest outbreaks.[6,pg.139]
Herbicide-tolerant crops are designed to make it easier for
farmers to use certain herbicides. A 1999 study of soybean
farming in the U.S. midwest found that farmers planting Roundup
Ready soybeans used 2 to 5 times as many pounds of herbicide per
acre as farmers using conventional systems, and ten times as much
herbicide as farmers using Integrated Weed Management systems,
which are intended to reduce the need for chemical
herbicides.[7,pg.2] Glyphosate, the active ingredient in Roundup,
can sometimes persist in soil over long periods of time and
may affect the growth of beneficial soil bacteria, among other
environmental effects. A recent, unpublished study conducted
at the University of Missouri suggests that applications of
Roundup to Roundup Ready crops may be associated with elevated
levels of soil fungi that sometimes cause plant diseases.
More hazards may lie ahead as new products of genetic engineering
come to market. According to the NEW YORK TIMES, Scotts Company
is collaborating with Monsanto to develop Roundup Ready grass for
lawns. Studies suggest that Roundup exposures can be harmful
to human health. For example, exposure to glyphosate herbicides
may be associated with increased occurrence of non-Hodgkins
lymphoma, a cancer of white blood cells. (See REHN #660.) And
a study published last August in ENVIRONMENTAL HEALTH
PERSPECTIVES found that in a laboratory, Roundup exposure
interfered with sex hormone production in cells of testicular
tumors taken from mice. If the introduction of Roundup Ready
grass leads to increased use of Roundup on lawns, children's
exposure to the herbicide could rise.
In some cases, genetically engineered crops might become problem
weeds, disrupting existing ecosystems. A recent study published
in NATURE found that some genetically engineered crops are
unlikely to become problem weeds. Researchers planted genetically
engineered crops that were available in 1990 and monitored their
growth for ten years. Many of the plants simply died out, and
those that did survive showed no signs of spreading. But some
crop plants, such as canola, survive well on their own without
human intervention. In Canada, genetically engineered canola
plants designed to resist various herbicides appear to have
exchanged genetic material so that some canola plants now can
survive exposure to two or three herbicides. These plants with
multiple herbicide resistance can be difficult for farmers to
Genetically engineered virus-resistant crops are supposed to
reduce problems from viral infections, but in some cases they
could make those problems worse. Virus-resistant crops are
created by adding virus genes to the plant's existing genetic
material. If a genetically engineered crop resistant to one virus
is infected by another virus, the genetic material from the two
viruses may sometimes interact to produce new virus types, which
could be more harmful or could infect a wider range of plants
than the original.[15,pgs.59-68]
All the hazards discussed above are compounded by the problem of
genetic pollution. Many crop plants disperse genetic material
through pollen, which may be carried by the wind or by
pollinators such as bees. This means genetically engineered
plants may "share" their genetic material with other,
non-engineered plants. For example, pollen from genetically
engineered corn can blow into a neighboring field and pollinate
conventional corn. Because of genetic pollution, some organic
farmers whose fields border genetically engineered crops may no
longer be able to certify their crops as organic.[6,pg.127]
In animals, sexual reproduction between different species is
usually impossible. In a few cases, reproduction between closely
related species can occur but the offspring are generally
sterile. For example, a horse and a donkey can mate to produce a
mule, but mules cannot reproduce. In contrast, many plants are
able to reproduce sexually with related species, and the
offspring of these combinations are often fertile. When crop
plants grow near wild plants to which they are related, they may
reproduce with these plants. This means that genetic material
inserted into a crop plant can find its way into wild plant
A recent article in SCIENCE reviews the literature on "ecological
risks and benefits" of genetically engineered crops and confirms
what advocates of precaution have been saying for years: we lack
basic information on how genetically engineered crops may affect
ecosystems. Here are a few examples of what scientists do not
know about ecological effects of genetically engineered crops:
** No published studies have looked at whether novel genes
introduced into crops have become established in populations of
wild relatives.[16, pg. 2088]
** We know that BT toxin can be released from the roots of BT
corn plants, but no published studies have looked at the
ecological consequences of adding BT toxin to soil in this way.
[16, pg. 2089]
** As we have seen, BT toxin in the digestive systems of
plant-eating insects may affect the predator insects that eat
them. Right now it is impossible to model how an ecosystem might
change due to these effects on predators, the authors say.[16,
** Scientists are currently unable to estimate the likelihood
that planting genetically engineered virus-resistant crops will
lead to the development of new types of plant viruses. [16, pg.
A precautionary approach would require that we investigate these
questions before, rather than after, permitting large-scale
commercial cultivation of genetically engineered crops.
[To be continued.]
*Rachel Massey is a consultant to Environmental Research
 John E. Losey and others, "Transgenic Pollen Harms Monarch
Larvae." NATURE Vol. 399, No. 6733 (May 20, 1999), pg. 214.
 Laura C. Hansen and John J. Obrycki, "Field Deposition of BT
Transgenic Corn Pollen: Lethal Effects on the Monarch Butterfly,"
OECOLOGIA Vol. 125, No. 2 (2000), pgs. 241-248.
 U.S. Environmental Protection Agency, "Biopesticide Fact
Sheet: BACILLUS THURINGIENSIS Cry1Ab Delta-Endotoxin and the
Genetic Material Necessary for Its Production (Plasmid Vector
pCIB4431) in Corn [Event 176]," April 2000. EPA Publication No.
730-F-00-003. Available at
 A. Hilbeck and others, "Effects of Transgenic BACILLUS
THURINGIENSIS corn-fed prey on Mortality and Development Time of
Immature CHYSOPERLA CARNEA (Neuroptera: Chrysopidae)."
ENVIRONMENTAL ENTOMOLOGY Vol. 27, No. 2 (April 1998), pgs.
 Deepak Saxena and others, "Insecticidal Toxin in Root
Exudates from BT Corn," NATURE Vol. 402, No. 6761 (December 2,
1999), pg. 480.
 Royal Society of Canada, ELEMENTS OF PRECAUTION:
RECOMMENDATIONS FOR THE REGULATION OF FOOD BIOTECHNOLOGY IN
CANADA (Ottawa: Royal Society of Canada, January 2001). ISBN
0-920064-71-X. Available from the Royal Society at (Ottawa,
Canada) phone: (613) 991-6990 or at
 Charles Benbrook, "Evidence of the Magnitude and Consequences
of the Roundup Ready Soybean Yield Drag from University-Based
Varietal Trials in 1998," AgBioTech InfoNet Technical Paper #1,
July 13, 1999. Available at
 U.S. Environmental Protection Agency, "Pesticide and
Environmental Fate One Line Summary: Glyphosate," May 6, 1993.
 See T. B. Moorman and others, "Production of Hydrobenzoic
Acids by BRADYRHIZOBIUM JAPONICUM strains after treatment with
glyphosate." JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY Vol. 40
(1992), pgs. 289-293. For a review of other relevant studies, see
Caroline Cox, "Herbicide Factsheet: Glyphosate (Roundup)" JOURNAL
OF PESTICIDE REFORM Vol. 18, No. 3 (Fall 1998), updated October
2000, available at http://www.pesticide.org/gly.pdf
 R.J. Kremer and others, "Herbicide Impact on FUSARIUM spp.
and Soybean Cyst Nematode in Glyphosate-Tolerant Soybean."
American Society of Agronomy study abstract, available at
http://www.biotech-info.net/fungi_buildup_abstract.html. Also see
University of Missouri press release, "MU Researchers Find Fungi
Buildup in Glyphosate-Treated Soybean Fields" (December 21,
2000), available at
 David Barboza, "Suburban Genetics: Scientists Searching for
a Perfect Lawn," NEW YORK TIMES July 9, 2000, pg. A1.
 Lennart Hardell and Mikael Eriksson, "A Case-Control Study
of Non-Hodgkin Lymphoma and Exposure to Pesticides," CANCER Vol.
85, No. 6 (March 15, 1999), pgs. 1353-1360.
 Lance P. Walsh and others, "Roundup Inhibits Steroidogenesis
by Disrupting Steroidogenic Acute Regulatory (StAR) Protein
Expression," ENVIRONMENTAL HEALTH PERSPECTIVES Vol. 108, No. 8
(August 2000), pgs. 769-776.
 M. Crawley and others, "Transgenic Crops in Natural
Habitats." NATURE Vol. 409, No. 6821 (February 8, 2001), pgs.
 Jane Rissler and Margaret Mellon, THE ECOLOGICAL RISKS OF
ENGINEERED CROPS (Cambridge, Mass.: MIT Press, 1996).
 L. L. Wolfenbarger and P.R. Phifer, "The Ecological Risks
and Benefits of Genetically Engineered Plants." SCIENCE Vol. 290
No. 5499 (December 15, 2000) pgs. 2088-2093.