The Ecological Impacts of Transgenic Crops on
Agroecosystem Health
Miguel
A. Altieri
Department of Environmental Science, Policy
and Management,
University of California, Berkeley
Introduction
Genetic
engineering is an application of
biotechnology involving the manipulation of
DNA and the transfer of gene components
between species in order to achieve stable
intergenerational expression of new traits.
In fact plant biotechnology is already
changing farming practices and is likely to
transform food production and impact the
environment in dramatic ways (OTA 1992).
During the twelve year period between 1986 to
1997, approximately 25,000 crop field trials
were conducted globally on more than 60 crops
with 10 traits in 45 countries (James C.
1997). The global arable land area devoted to
transgenic crops increased 4.5 fold from 2.8
million hectares in 1996 to 12.8 million
hectares in 1997, and no less than 30 million
hectares in 1998. USA accounted for 64% of
the global acreage, followed by China and
Argentina.
Although
there are many applications of genetic
engineering in agriculture, the current focus
of biotechnology is to generate transgenic
crops such as herbicide resistant crops
(HRCs) and pest and disease resistant crops.
HRCs and insect resistant crops (Bt crops)
accounted for 54 and 31% of the total global
area in 1997. Increasingly, large acreages of
transgenic soybean (18 million hectares),
maize (10 million hectares), potato, tomato,
tobacco, and cotton are being commercially
deployed in agricultural landscapes worldwide
(James C. 1997). Transnational corporations
(TNCs) such as Monsanto, DuPont, Norvartis,
etc. which are the main proponents of
biotechnology argue that carefully planned
introduction of these crops should reduce or
even eliminate the enormous crop losses due
to weeds, insect pests, and pathogens. In
fact they argue that the use of such crops
will have added beneficial effects on the
environment by significantly reducing the use
of agrochemicals. What is ironic is the fact
that the biorevolution is being brought
forward by the same interests that promoted
the first wave of agrochemically-based
agriculture, but this time, by equipping each
crop with new “insecticidal genes,”
they are promising the world safer
pesticides, reduction on chemically intensive
farming and a more sustainable agriculture.
As
long as transgenic crops follow closely the
pesticide paradigm, such biotechnological
products will do nothing but reinforce the
pesticide treadmill in agroecosystems, thus
legitimizing the concerns that many
scientists have expressed regarding the
possible environmental risks of genetically
engineered organisms. Given the power of
biotechnology to produce combinations of
genes not found in nature, the most serious
ecological risks posed by the
commercial-scale use of transgenic crops are
(Rissler and Mellon 1996; Krimsky and Wrubel
1996):
The spread of transgenic
crops threatens crop genetic diversity by
simplifying cropping systems and
promoting genetic erosion;
The potential transfer of
genes from HRCs to wild or
semi-domesticated relatives thus creating
super weeds;
HRC volunteers become weeds
in subsequent crops;
The use of HRCs undermine
the possibilities of crop diversification
thus reducing agrobiodiversity in time
and space;
Vector-mediated horizontal
gene transfer and recombination to create
new pathogenic bacteria;
Vector recombination to
generate new virulent strains of virus,
especially in trangenic plants engineered
for viral resistance with viral genes;
Insect pests will quickly
develop resistance to crops with Bt
toxin;
Massive
use of Bt toxin in crops can unleash
potential negative interactions affecting
ecological processes and non-target organisms
including beneficial insects and soil biota.
The
above impacts of agricultural biotechnology
are here in evaluated in the context of
agroecological goals aimed at making
agriculture more socially just, economically
viable, and ecologically sound (Altieri
1996). Such evaluation is timely given the
explosion of transgenic crop cultivation
world wide, despite the fact that in most
countries (especially in the developing
world) stringent procedures are not in place
to anticipate risk or to deal with
environmental problems that may develop when
engineered plants are released into the
environment (Hruska and Lara Pavón 1997).
This issue has received some discussion in
government, international, and scientific
circles, but often from a narrow perspective
that has downplayed the seriousness of the
risks (Kendall et al. 1997; Royal Society
1998). In fact methods for risk assessment of
transgenic crops are just being proposed
(Kjellsson and Simmsen 1994) and there is
justifiable concern that current field
biosafety tests tell little about potential
environmental risks associated with
commercial-scale production of transgenic
crops. A main concern is that international
pressures to gain markets and profits is
resulting in companies releasing transgenic
crops too fast, without proper consideration
for the long-term impacts on people or the
ecosystem (Mander and Goldsmith 1996).
Actors
and Research Directions
Most
innovations in agricultural biotechnology are
profit driven rather than need driven,
therefore the thrust of the genetic
engineering industry is not really to solve
agricultural problems, but to create
profitability. This statement is supported by
the fact that at least 27 corporations have
initiated herbicide-tolerant plant research,
including the world’s eight largest
pesticide companies Bayer, Ciba-Geigy, ICI,
Rhone-Poulenc, Dow/Elanco, Monsanto, Hoescht
and DuPont, and virtually all seed companies,
many of which have been acquired by chemical
companies (Gresshoft, 1996). Monsanto has
acquired Dekalb, Asgrow, and Delta and Pine
land while AgrEvo acquired Sun Seeds and
Dupont made an alliance with Pioneer. The
buying of independent seed companies has
concentrated the control of multinational
companies over key genetic sources crucial
for the improvement of agriculture (Hobbelink
1991).
In
the industrialized countries from 1986-1992,
57% of all field trials to test transgenic
crops involved herbicide tolerance and 46% of
applicants to the USDA for field testing were
chemical companies. Crops currently targeted
for genetically engineered tolerance to one
or more herbicides includes: alfalfa, canola,
cotton, corn, oats, petunia, potato, rice,
sorghum, soybean, sugarbeet, sugar cane,
sunflower, tobacco, tomato, wheat and others.
It is clear that by creating crops resistant
to its herbicides a company can expand
markets for its patented chemicals. MacKenzie
(1996), gave a value of 75 million dollars
for HRCs in 1995, the first year they were
marketed, and indicates by the year 2000 the
market will be approximately 805 million
dollars, representing a 61% growth. It is
also estimated that by the year 2000, the
market value of insecticide resistant crops
will be about 500 million dollars.
Although
some testing is being conducted by
universities and advanced research
organizations, the research agenda of such
institutions is being increasingly influenced
by the private sector in ways never seen in
the past. 46% of biotechnology firms support
biotechnology research at universities, while
33 of the 50 states have university-industry
centers for the transfer of biotechnology.
The challenge for such organizations will not
only be to ensure that ecologically sound
aspects of biotechnology are researched and
developed (N fixing, drought tolerance,
etc.), but to carefully monitor and control
the provision of applied non-proprietary
knowledge to the private sector so as to
protect that such knowledge will continue in
the public domain for the benefit of all
society. But given the current nature of
university-industry partnerships exemplified
by the recent agreement between the
University of California, Berkeley and
Novartis, cast no doubt on how TNCs can
control public research to their advantage.
Biotechnology
and Agrobiodiversity
Although
biotechnology has the capacity to create a
greater variety of commercial plants, the
trends set forth by TNCs is to create broad
international markets for a single product,
thus creating the conditions for genetic
uniformity in rural landscapes. In addition,
patent protection and intellectual property
rights as espoused by World Trade
Organization (WTO), inhibiting farmers from
re-using, sharing and storing seeds raises
the prospect that few varieties will dominate
the seed market. In fact companies such as
Monsanto, make sure that farmers depend on
their seeds by asking them to sign an
agreement promising not to plant seeds their
crops produce. Moreover, Monsanto hopes to
enforce biologically what it cannot enforce
contractually by designing crops whose seeds
they carry will lose the ability to
reproduce. Such seed-sterilizing technology
has been dubbed Terminator Technology and
poses major threats to one of the most viable
methods of maintaining genetic diversity: the
ability of farmers to store, re-plant, and
share seeds. Although a certain degree of
crop uniformity may have certain economic
advantages, it has two ecological drawbacks.
First, history has shown that a huge area
planted to a single cultivar is very
vulnerable to a new, matching strain of a
pathogen or pest. And, second, the widespread
use of a single cultivar leads to a loss of
genetic diversity (Robinson 1996).
Evidence
from the Green Revolution clearly shows that
the spread of modern varieties has been an
important cause of genetic erosion, as
massive government campaigns encouraged
farmers to adopt modern varieties and to
abandon many local varieties (Tripp 1996).
The uniformity caused by increasing areas
sown to a smaller number of varieties is a
source of increased risk for farmers, as the
varieties may be more vulnerable to disease
and pest attack and most of them perform
poorly in marginal environments (Robinson
1996).
All
the above effects are not ubiquitous to
modern varieties and it is expected that,
given their monogenic nature and fast acreage
expansion, transgenic crops will only
exacerbate such effects.
Environmental
Problems of Herbicide Resistant Crops
Resistance
According
to proponents of HRCs, this technology
represents an innovation that enables farmers
to simplify their weed management
requirements, by reducing herbicide use to
post-emergence situations using a single,
broad-spectrum herbicide that breaks down
relatively rapidly in the soil. As subsidies
drop, it may no longer be economical to
control weeds with expensive herbicides, thus
developing HRCs for lower cost herbicides may
be the solution. Herbicide candidates with
such characteristics include Glyphosate,
Bromoxynil, Sulfonylurea, Imidazolinones,
Glufosinate Ammonium among others.
However,
in actuality, the use of herbicide-resistant
crops is likely to increase the use of
specific herbicides and given herbicide
volumes and acreage coverage (in 1997 50,000
farmers grew 3.6 million hectares of HR
soybeans, equivalent to 13% of the 71 million
national soybean acreage in the USA),
production costs are likely to increase.
Although industry claims that HRCs have
enhanced yield dependability, soil and water
conservation and are compatible with minimum
tillage systems, ecologists predict a number
of serious environmental problems associated
with such crops.
Herbicide
Resistance
It
is well documented that when a single
herbicide is used repeatedly on a crop, the
chances of herbicide resistance developing in
weed populations greatly increases (Holt et
al. 1993). About 216 cases of pesticide
resistance have now been reported in one or
more herbicide chemical families (Holt and Le
Baron 1990). Triazine herbicides have the
most resistant weed species (about 60), but
the sulfonylureas and the imidazolinones are
also particularly prone to the rapid
evolution of resistant weeds and up to now
fourteen weed species have become resistant
to sulfonylurea herbicides. Cocklebur an
aggressive weed of soybean and corn in the
southeastern USA has exhibited resistance to
imidazolinone herbicides. Many weed grasses
now exhibit multiple herbicide resistances
(Goldberg 1992).
The
problem is that given industry pressures to
increase herbicide sales, acreage treated
with these broad-spectrum herbicides will
expand, exacerbating the resistance problem.
For example, it has been projected that the
acreage treated with glyphosate will increase
to nearly 150 million acres. Although
glyphosate is considered less prone to weed
resistance, the increased use of the
herbicide will result in weed resistance,
even if more slowly, as it has been already
documented with Australian populations of
annual ryegrass, quackgrass, birdsfoot
trefoil and Cirsium arvense (Gill 1995).
Ecological
Impacts of Herbicides
Companies
affirm that bromoxynil and glyphosate, when
properly applied, degrade rapidly in the
soil, do not accumulate in groundwater, have
no effects on non-target organisms, and leave
no residues in food. There is, however,
evidence that bromoxynil causes birth defects
in laboratory animals, is toxic to fish, and
may cause cancer in humans (Goldburg 1992).
Because bromoxinil is absorbed dermally, and
because it causes birth defects in rodents,
it is likely to pose hazards to farmers and
farm workers. Similarly glyphosate has been
reported to be toxic to some non-target
species in the soil -both to beneficial
predators such as spiders, mites, carabid and
coccinellid beetles and to detritivores such
as earthworms, as well as to aquatic
organisms, including fish (Pimentel et al.
1989). As this herbicide is known to
accumulate in fruits and tubers as it suffers
little metabolic degradation in plants,
questions about food safety also arise.
Transgenic
Crops as WeedS
Some
scientists have suggested that some
transgenes may confer or enhance weediness in
some crops, thereby enhancing their capacity
to persist in agricultural fields. Most
genetically engineered plants would not be
expected to become weeds; those that do,
however, present serious problems (Radosevich
et al. 1996). This is the case of transgenic
seeds that at harvest shatter to the ground
and germinate the following year in
rotational crops. If these “volunteer
weeds” are resistant to herbicides being
used in the new crop, competition may become
critically yield limiting.
Creation
of “Super Weeds”
Although
there is some concern that transgenic crops
themselves might become weeds, a major
ecological risk is that large scale releases
of transgenic crops may promote transfer of
transgenes from crops to other plants, which
may then become weeds (Darmency 1994).
Transgenes that confer significant biological
advantages may transform wild/weedy plants
into new or worse weeds (Rissler and Mellon
1996). The biological process of concern here
is introgression, that is, hybridization
among distinct plant species. Evidence
indicates that such genetic exchanges among
wild, weed and crop plants already occur. The
incidence of shattercane (Sorghum bicolor), a
weedy relative of sorghum and the gene flows
between maize and teosinte demonstrates the
potential for crop relatives to become
serious weeds. This is worrisome given that a
number of US crops are grown in close
proximity to sexually compatible wild
relatives (Lutman 1999). Extreme care should
be taken in plant systems exhibiting easy
cross-pollination such as oats, barley,
sunflowers, and wild relatives and between
rapseed and related crucifers. In Europe
there is a major concern about the
possibility of pollen transfer to herbicide
tolerant genes from Brassica oilseeds to
Brassica nigra and Sinapis arvensis (Casper
and Landsmann 1992) There are also crops that
are grown near wild/weedy plants that are not
close relatives but may have some degree of
cross compatibility such as the crosses of
Raphanus raphanistrum R. X Sativus (radish)
and Johnson grass X Sorghum corn (Radosevich
et al. 1996). Cascading repercussions of
these transfers may ultimately mean changes
in the make-up of plant communities and
especially pose major threats to centers of
diversity. Transfer of genes from transgenic
crops to organically grown crops poses
specific problems to organic farmers as
organic certification depends on the growers
being able to guarantee that their crops have
no inserted genes. Crops able to outbreed
such as maize or oilseed rape will be
affected to the greatest extent, but all
organic farmers are at risk of contamination
as there are no regulations that enforce
minimum isolating distances between
transgenic and organic fields.
Reduction
of Agroecosystem Complexity
Total
weed removal via the use of broad-spectrum
herbicides may lead to undesirable ecological
impacts, given that an acceptable level of
weed diversity in and around crop fields has
been documented to play important ecological
roles such as enhancement of biological
insect pest control, better soil cover
reducing erosion, etc. (Altieri 1994). HRCs
will most probably enhance continuous
cropping by inhibiting the use of rotations
and polycultures susceptible to the
herbicides used with HRCs. Such impoverished,
low plant diversity agroecosystems provide
optimal conditions for unhampered growth of
weeds, insects and diseases because many
ecological niches are not filled by other
organisms. Moreover, HRCs, through increased
herbicide effectiveness, could further reduce
plant diversity, favoring shifts in weed
community composition and abundance, favoring
competitive species that adapt to these
broad-spectrum, post emergence treatments
(Radosevich et al. 1996).
Environmental
Risks of Insect Resistant Crops Resistance
According
to the industry, the promise of transgenic
crops inserted with Bt genes is the
replacement of synthetic insecticides now
used to control insect pests. The gene coding
for Bt toxin production was introduced into
cotton and the first commercial planting of
transgenic cotton occurred in 1996.
Productivity was higher than for
non-transgenic cotton, but was not as high as
expected. Problems arose in the USA because
of a particularly heavy infestation of
bollworm in 800,000 hectares, causing heavy
feeding damage. The infestation was
controlled using conventional insecticides
(Peferoen 1997). Because most crops have a
diversity of insect pests, insecticides will
still have to be applied to control
non-Lepidoptera pests, which are not
susceptible to the endotoxin expressed by the
crop (Gould 1994). In fact, in a recent
report (USDA, 1999) an analysis of pesticide
use in the 1997 growing season in 12
region/crop combinations showed that in 7
sites no statistically significant
differences in pesticide use on Bt crops
versus non-Bt crops. In the Mississippi
Delta, significantly more pesticides were
used on Bt versus non-Bt cotton.
On
the other hand, several Lepidoptera species
have been reported to develop resistance to
Bt toxin in both field and laboratory tests,
suggesting that major resistance problems are
likely to develop in Bt crops which through
the continuous expression of the toxin create
a strong selection pressure (Tabashnik 1994).
Industry however, claims that transgenic
plants expressing high levels of endotoxin
represent a different type of selective
pressure, that is a chronic high-dose
exposure. No reports of resistance to chronic
high-dose exposure of Bt endotoxins are yet
known. Moreover, given that a diversity of
different Bt-toxin genes have been isolated,
biotechnologists argue that if resistance
develops alternative forms of Bt toxin can be
used (Kennedy and Whalon 1995). However,
because insects are likely to develop
multiple resistance or cross-resistance, such
strategy is also doomed to fail (Alstad and
Andow 1995). In fact, scientists have already
detected development of “behavioral
resistance” by some insects that take
advantage of the fact that expression of
toxin potency is uneven within crop foliage,
thus attacking tissue patches with low toxin
concentrations. Moreover, as genetically
inserted toxins often decrease in leaf and
stem titer as crops reach maturation, the low
dose can only kill or debilitate completely
susceptible larvae (homozygotes) and
consequently adaptation to the Bt toxin can
occur much faster if the concentration always
remained high. Observation of transgenic corn
plants in late October indicated that most
European corn borers that survived had
entered diapause in preparation for emergence
in the following spring as adults (Onstad and
Gould 1998).
Others,
borrowing from past experience with
pesticides, have proposed resistance
management plans with transgenic crops, such
as the use of seed mixtures and refuges
(Tabashnik 1994). Patchworks of transgenic
and non-transgenic crops can delay the
evolution of resistance by providing
susceptible insects for mating with resistant
insects. The crops in the refuge are likely
to sustain heavy damage; a refuge kept
completely free of pesticides must be 20-30%
the size of the engineered plot. The refuge
should be about 40% the size of the
biotechnology plot if pesticides are to be
used, since insecticides spraying can
increase the odds of Bt resistance
developing. According to members of the
Campaign for Food Safety, Monsanto’s new
plan calls for only 20% refuges even when
insecticides are to be used. Moreover, the
plan offers no details whether the refuges
must be planted along side the transgenic
crops, or at some distance away, where
studies suggest they would be less effective
(Mallet and Porter 1992). Recent laboratory
results with a worldwide pest, the pink
bollworm, contradict an important assumption
of the refuge strategy. Liu et al. (1999)
found that a resistant pink bollworm larva
strain on Bt cotton took longer to develop
than susceptible larvae on non-Bt cotton.
This development asynchrony favors random
mating that could reduce the excpected
benefits of the refuge strategy.
In
addition for refuges to requiring the
difficult goal of regional coordination
between farmers, it is unrealistic to expect
most small and medium sized farmers to devote
up to 30-40 % of their crop area to refuges,
especially if crops in these areas are to
sustain heavy pest damage. It is likely that
development of resistance will be influenced
both by the insect and crop in question. For
example, it may be argued that for the
European corn borer that has a low number of
generations per year and feeds on numerous
other host plants besides corn, resistance is
a small issue. However, given the fast
expansion of transgenic crop monocultures
worldwide (from 2.8 million hectares in 1996
to 34 million in 1998) that occur at the
expense of natural vegetation and other
crops, the availability of alternative host
plants can decrease considerably (Kendall et
al. 1997).
Effects
on beneficial insects
By
keeping pest populations at extremely low
levels, Bt crops could potentially starve
natural enemies, as these beneficial insects
need a small amount of prey to survive in the
agroecosystem. Among the natural enemies that
live exclusively on insects which the
transgenic crop is designed to kill
(Lepidoptera), egg and larval parasitoids
would be most affected because they are
totally dependent on live hosts for
development and survival, whereas some
predators could theoretically thrive on dead
or dying prey.
Natural
enemies could also be affected directly
through inter-trophic level effects of the
toxin. The potential of Bt toxins moving
through arthropod food chains poses serious
implications for natural biocontrol in
agroecosystems. Evidence from studies
conducted in Scotland suggest that aphids
were capable of sequestering the toxin from
Bt crops and transferring it to its
coccinellid predators, in turn affecting
reproduction and longevity of the beneficial
beetles (Birch 1997). Similarly, studies in
Switzerland show that mean total mortality of
Lacewing larvae (Chrysopidae) raised on Bt
fed prey was 62% compared to 37% when raised
on Bat-free prey. These Bt prey fed
Chrysopidae also exhibited prolonged
development time throughout their immature
life stage (Hilbeck et al. 1998). In studies
involving the diamondback moth and its
parasitic wasp (Cotesia plutellae) parasitic
larvae forced to develop in Bt-treated
susceptible moth larvae inevitably died with
their hosts (Schuler et al. 1999). These
results could be questioned on the basis that
they came from small-scale laboratory assays
in which insects were exposed to high levels
of transgenically expressed toxin in no
choice tests. But such no choice situations
will increasingly become the norm in field
conditions as Bt crops massively inundate the
landscape.
Effects
on soil biota
Bt
toxins can be incorporated into the soil
through leaf materials, when farmers
incorporate crop residues after harvest.
Toxins may persist for 2-3 months, resisting
degradation by binding to clay and humic acid
soil particles while maintaining toxin
activity (Palm et al. 1996). Such active Bat
toxins that end up and accumulate in the soil
and water from transgenic leaf litter may
have negative impacts on soil and aquatic
invertebrates and nutrient cycling processes
(Donnegan et al. 1995).
Perturbations
have been recorded by several authors with
the introduction in the soil of genetically
modified micro organisms (such as Pseudomonas
fluorescens), including displacement of
indigenous populations, suppression of fungal
populations, reduced protozoa populations,
altered soil enzymatic activity, and
increased carbon turnover (Naseby and Lynch
1998). These authors call for more research
on the consequences of the release of novel
organisms in the rhizosphere before they can
be safely utilized.
Downstream
Effects
A
major environmental consequence resulting
from the massive use of Bt toxin in cotton or
other crops occupying a larger area of the
agricultural landscape, is that neighboring
farmers who grow crops other than cotton, but
that share similar pest complexes, may end up
with resistant insect populations colonizing
their fields. As Lepidopteran pests that
develop resistance to Bt cotton move to
adjacent fields where farmers use Bt as a
microbial insecticide, this may render
farmers defenseless against such pests, as
the biopesticide becomes ineffective thus
losing an important biological control tool
(Gould 1994). Among those most affected would
be organic farmers who rely on Bt based
microbial insecticides for their pest
management programs. Recent findings by Losey
et al. (1999) showing that corn pollen
containing Bat toxin can drift several meters
downwind and deposit itself on milkweed
foliage with potentially deleterious effects
on monarch butterfly populations, opens a
whole new dimension on the unexpected impacts
of transgenic crops on non-target organisms.
Impacts
of Disease Resistant Crops
Scientists
have attempted to engineer plants for
resistance to pathogenic infection by
incorporating genes for viral products into
the plant genome. The most common method is
to use viral RNA sequences which when
inserted into plants and expressed, interfere
with the infecting virus to give what is
called “pathogen derived
protection”. Although the use of viral
genes for resistance in crops to virus has
potential benefits, there are some risks.
First, in plants containing coat protein
genes, there is a possibility that such genes
will be taken up by unrelated viruses
infecting the plant. In such situations, the
foreign gene changes the coat structure of
the viruses and may confer properties such as
changed method of transmission between
plants. The second potential risk is that
recombination between RNA virus and a viral
RNA inside the transgenic crop could produce
a new pathogen leading to more severe disease
problems. Some researchers have shown that
recombination occurs in transgenic plants and
that under certain conditions it produces a
new viral strain with altered host range
(Steinbrecher 1996).
The
possibility that transgenic virus-resistant
plants may broaden the host range of some
viruses or allow the production of new virus
strains through recombination and
transcapsidation demands careful further
experimental investigation (Paoletti and
Pimentel 1996).
The
Performance of Field-Released Transgenic
Crops
Up
to 1995, more than 2000 small-scale field
trials of genetically engineered plant
species have been carried out in the United
States. Until early 1997, thirteen
genetically modified crops had been
deregulated by the USDA which were already on
the market or in the fields for the first
time. Over 20% of the US soybean acreage was
planted with roundup tolerant soybean and
about 400,000 acres of maximizer Bt corn were
planted in 1996. Worldwide, such acreage
expanded considerably in 1998 (transgenic
cotton: 6.3 million acres, transgenic corn:
20.8 million acres and soybean: 36.3 million
acres) due to marketing and distribution
agreements entered into by corporations and
marketers (i.e. Ciba Seeds with Growmark and
Mycogen Plant Sciences with Cargill).
Given
the speed, with which products move from
laboratory testing to field production, the
question arises whether transgenic crops meet
the expectations of the biotechnology
industry. According to evidence presented by
the Union of Concerned Scientists, there are
already signals that the commercial-scale use
of some transgenic crops pose serious
ecological risks and do not deliver the
promises of industry (Table 1). A recent
study by the USDA Economic Research Service
(USDA 1999) shows that in 1998 yields were
not significantly different in engineered
versus nonengineered crops in 12 of 18
crop/region combinations. In the six
crop/region combinations were Bat crops or
HRCs fared better, they exhibited increased
yields between 5-30%. Glyphosphate tolerant
cotton showed no significant yield increase
in either region where it was surveyed.
The
appearance of “behavioral
resistance” by bollworms in cotton, that
is that the herbivore was capable of finding
plant tissue areas with low Bat
concentrations, raises questions not only
about the adequacy of the resistance
management plans being adopted, but also
about the way biotechnologists underestimate
the capacity of insects to overcome genetic
resistance in unexpected manners (The Gene
Exchange 1996)
Similarly
poor harvests of herbicide resistant cotton
due to phytotoxic effects of Roundup in four
to five thousand acres in the Mississippi
Delta (New York Times 1997) points at the
erratic performance of HRCs when subjected to
varying agroclimatic conditions. Monsanto
claims that this is a very small and
localized incident that is being used by
environmentalists to overshadow the benefits
that the technology brought on 800,000 acres.
From an agroecological standpoint however,
this incident is quite significant and merits
further evaluation, since assuming that a
homogenizing technology will perform well
through a range of heterogeneous conditions
has no scientific basis. There is also much
concern about the fact that the hundreds of
small-scale test carried mostly by private
companies, do not capture the full dimensions
of the environmental fate of field deployed
transgenic crops. Tests are usually limited
to prevent escape of pollen, seeds, or other
propagules. Experimental tests are usually
carried in small plots and are of short
duration (one season) and thus undesirable
effects on non-target organisms are unlikely
to be observed (Snow and Moran 1997).
Conclusions
We
know from the history of agriculture that
plant diseases, insect pests and weeds become
more severe with the development of
monoculture, and that intensively managed and
genetically manipulated crops soon lose
genetic diversity (Altieri 1994; Robinson
1996). Given these facts, there is no reason
to believe that resistance to transgenic
crops will not evolve among insects, weeds
and pathogens as has happened with
pesticides. No matter what resistance
management strategies will be used, pests
will adapt and overcome the agronomic
constraints (Green et al. 1990). Studies of
pesticide resistance demonstrate that
unintended selection can result in pest
problems that are greater than those that
existed before deployment of novel
insecticides. Diseases and pests have always
been amplified by changes toward homogeneous
agriculture (Robinson 1996).
The
fact that interspecific hybridization and
introgression are common to species such as
sunflower, maize, sorghum, oilseed rape,
rice, wheat and potatoes provides a basis to
expect gene flow between transgenic crops and
wild relatives to create new herbicide
resistant weeds (Lutman 1999). There is
consensus among scientists that transgenic
crops will eventually allow transgenes to
escape into free living populations of wild
relatives. The disagreement lies in how
serious are the impacts (Casper and Landsmann
1992). Despite the fact that some scientists
argue that genetic engineering is not
different than conventional breeding, critics
of biotechnology claim that DNA technology
enables new (exotic) genes into transgenic
plants. Such gene transfers are mediated by
vectors which are derived from
disease-causing viruses or plasmids, which
can breakdown species barriers so that they
can shuttle genes between a wide range of
species thus infecting many other organisms
in the ecosystem (Steinbrecher 1996).
