Genetic Engineering in Agriculture
and the Environment
Assessing risks and benefits
Maurizio G. Paoletti and David Pimentel
'WOrldWide, almost 90% of
.
. the human food supply is
. provided by only 15 crop
species and 8 livestock species, small
numqers when compared with the
.estirriated 10-30 million species in.habiting our biosphere (Paoletti and
Pimcrntel 1992). Introducing genes
from various organisms into crops
and livestock has long been regarded
·as a promising way to ensure the
~ontinued productivity of agriculture and forestry (Beringer et al.
1992, Gasser and Fraley 1989, HarJander 1989, Jensen 1988, Lehrman
1992). Then, too, the substitution or
addition of diverse genes into agricultural and forestry species may, as
Raven (1992) has suggested, be a
,wa y to use the undiscovered resources of biodiversity in the service
~of social and economic development.
. Genetic engineering technology
~has dramatically reduced the time
required for the development of new
commercial varieties of crops. Some
investigators have suggested that the
use of genetic markers could reduce
the usual 1 0-15 -year breeding cycles
to only 2-3 years (Kidd 1994). Genetic engineering is rapidly replacing
traditional plant breeding programs
and has become the mainstay of agMaurizio G. Paoletti is a professor in
the Department of Biology, Padova University, Via Treste 75, Padova, Italy.
David Pimentel is a professor in the
Department of Entomology and Section
of Ecology and Systematics, Cornell
University, Ithaca, NY 14853. © 1996
American Institute of Biological Sciences.
October 1996
Genetic engineering is
rapidly replacing
traditional plant
breeding programs and
has become the
mainstay of
agricultural crop
improvement
ricultural crop improvement. Since
1986, 2053 field trials have led to
the release of transgenic plants into
natural ecosystem~ around the world
(Krattiger and Rosemarin 1994).
Recent advances in the genetic engineering of plants, animals, and microorganisms, including viruses, are
encouraging and show promise for
further development (FessendenMcDonald 1992, Gasser and Fraley
1989, Mellon and Rissler 1995,
Meeusen and Warren 1989, Moffat
1986). Meanwhile, research efforts
are increasing at university, industry, and government laboratories.
In addition to the perceived benefits of genetic engineering for the
industrialized nations, proponents
advocate the use of genetic engineering to improve agriculture in developing countries. This strategy might
help these countries bypass expensive, high-input crop production and
move their traditional agriculture
toward low-input sustainable prac-
tices (Odum 1989).
Many scientists, however, have
expressed concern regarding the possible environmental risks of genetically engineered organisms (Buttel
1995, Buttel et al. 1985, Colwell et
al. 1985, Mellon 1988, Pimentel et
al. 1989, Simberloff 1986, Vitousek
1985, Wrubel et al. 1992). Many
have asserted that the release of genetically engineered organisms might
adversely affect both tropical and
temperate biodiversity (Altieri and
Merrick 1988, Cook et al. 1991,
Hanson et al. 1991, Paoletti and
Pimentel 1992, Pimentel et al. 1992,
Wolf 1985).
If, as expected, the US government deregulates testing, leaving it
entirely to the discretion of those
with economic interests in genetic
engineering, the release of genetically engineered organisms before
their safety has been ascertained will
be a danger. Some proponents of
genetic engineering support deregulation of biotechnology. However,
will reducing regulations, as suggested by Miller (1994), reduce the
risks of genetic engineering?
In this article we assess the current status of the genetic engineering
of plants, animals, and microorganisms used in agriculture. We also
analyze the benefits and risks this
promising technology might have for
the future of sustainable agriculture
and the environment.
Risks and benefits
Although genetic engineering can
improve the control of pest insects,
665
plant pathogens, and weeds, there
are risks associated with it.
Table 1. Summary of field trial approvals granted by trait (OEeD database IX
1993). The total number of approvals with trait characters is greater than the
number of individual approvals recorded because a number of approvals have been
granted for releases in which more than one trait has been introduced into a crop
host.
Insect pest control. The gene for the
Bt toxin, fr~m the bacterium Bacillus thuringiensis, has been introduced
Approvals granted
Minimal estimate of sites approved
into more than 50 plant crops (Adang
1991, Beegle and Yamamoto 1992, Trait
Number
% of total
Number
% of total
Gelernter 1990, Skot et al. 1990).
489
38.9
685
41.7
Plants expressing this gene demon- Herbicide tolerance
56
3.4
Disease resistance
35
2.8
strate effective control of such pests Virus
144
resistance
9.1
8.8
115
as caterpillars and beetles. In addi- Insect resistance
134
8.2
7.1
89
tion, engineered Bt has been ap- Use of markers
442
26.9
382
30.4
72
5.7
81
4.9
proved for use as a conventional Quality traits
7
0.4
Flower color
5
0.4
insecticide (Lereclus et al. 1995).
18
1.4
Research studies
19
1.2
Although in field trials, Bt toxin- Male sterility
3.1
61
39
3.7
expressing cotton can effectively re- Resistance to stress
9
0.5
0.7
9
3
0.2
3
0.2
pel caterpillars, a thorough assess- Heavy metal tolerance
1
1
0.1
0.1
ment of the effects on nontarget Other
1257
100.0
1642
100
organisms has not been made (Wil- Total releases
son et al. 1992). However, several
lepidopteran species have been re- when a pest population was exposed for agricultural use in plant pathoported to develop resistance to Bt to more than one toxin at a time gen control (Hawksworth and
toxin in both field and laboratory (Hofte and Whiteley 1989, Pimentel Mound 1991, May 1991). Hynes
te~ts (Lambert and Peferoen 1992, and Bellotti 1976) and/or when un- (1986) and Yoder et al. (1986) develStone et al. 1991, Tabashnik et al. treated refuges were provided to con- oped modified Aspergillus nidulans
1992). This finding suggests that serve nonresistant genotypes. 2
and Helminthosporium maydis, and
In addition, some viruses can be Staples et al. (1988) transformed an
ritajor resistance problems are likely
to develop if the Bt toxin is widely genetically engineered to have en- entomophagous fungus, Metarintroduced into major crops such as hanced pathogenicity for insect con- hyzium anisopliae, with a plasmid
corn, cotton, and wheat. However, trol and not persist in the environ- containing a gene for resistance to
because an abundance of Bt species ment (Tomalski and Miller 1991, benomyl, a broad-scale fungicide
and genetic lines live in soil, some Wood and Granados 1991). These (Staples et al. 1988). This product
alternative forms of Bt toxin exist latter pathogens have great potential will help protect plants because heavy
that can be used if resistance devel- for pest control. Engineered viruses applications of fungicide can be used
ops to the form that is currently used have been experimentally released in on the crop without reducing the
(Lambert and Peferoen 1991, Mar- Britain (Bishop et al. 1988) and in effectiveness of the entomophagus
the United States at Geneva, New fungus. To protect chestnuts against
tin and Travers 1989).
The environmental consequences York, 3 for insect pest control. Thus chestnut blight, hypovirulent modiof the massive use of Bt toxin in far, the results appear encouraging. fied strains of Cryphonectria parasitica have been developed (Polashock
cotton and other major crops remain
unknown. There are questions about Plant pathogen control. In 1988 a et al. 1994). Fusarium graminearum
the toxin's potential interaction with genetically engineered bacterial has been modified to inhibit syntheother organisms in the environment strain, K1026, of Agrobacterium sis of trichothene toxins and reduce
radiobacter (Jones and Kerr 1989) diseases in some plant hosts. Em(Jepson et al. 1994).
Roush et al. 1 developed a promis- was released commercially to con- ploying genetic engineering to ining model to evaluate the advantage trol crown gall (Agrobacterium crease host plant resistance to pathoof reducing pest resistance to Bt- tumefaciens) disease of stone fruit genic fungi is another promising goal.
Some genes derived from plant
engineered plants by having Bt ex- trees (e.g., peach, cherry, and alpressed only when and where needed. mond) in Australia (Kerr 1991). This RNA viruses confer virus resistance
Bt toxins also might be expressed recombinant organism was the first in transgenic crop plants. A squash
only moderately, so that not all sus- to be released for commercial use in recently developed by Asgrow Seed
ceptible individuals would be killed agriculture for disease control, and Company has been approved for
by the engineered plant. An addi- so far it has proven highly effective. commercialization in the United
Although an estimated 1.5 mil- States. Also, approximately 5% of
tional step would involve the use of
mixtures of Bt toxins within each lion fungi species exist, little has tobacco cultivated in China has been
plant. In ecological studies, the de- been done to genetically modify fungi modified to be resistant to Tobacco
Mosaic Virus (TMV). Engineered
velopment of resistance was delayed
tobacco with double resistance to
2See footnote 1.
TMV
and CMV (Cauliflower Mo3H.A. Wood, 1992, personal commimication.
lR. T. Roush, M. Burgess, and W. McGaughey,
.1993, unpublished manuscript. Cornell Uni- Boyce Thompson Institute, Cornell Univer- saic Virus) is now under trial
(Krattiger 1994). Approximately 8%
sity, Ithaca, NY.
versity, Ithaca, NY.
.
666
BioScience Vol. 46 No.9
able 2. Annual field trial approvals granted-by crop (OECD database IX 1993).
Numbers granted each year
1986
1987
1988
1989
1990
1991
1
7
4
3
Ifalfa
llegheny
pple
,Asparagus
~Broccoli
Canol a
,cantaloupe
Carnation
1
1
5
15
hicory
~hrysanthemum
auliflower
1
41
7
1
>
Corn
'Cotton
Cucumber
'1flax
Kiwi fruit
lLettuce
Melon
Papaya
Petunia'
Poplar
Potato
Rice I
SoybJan
'Squa~h
Suga,rbeet
Sunflower
Tobacco
Tomato
Walnut
""Others
Total
5
1
1
8
2
2
12
4
1
1
1
3
3
7
12
9
7
1
1
1
9
37
69
of approved field trials (Table 1) are
'transgenic virus-resistant plants
(AIBS 1995). Although the use of
viral genes for resistance in plants to
virus pathogens has potential benefits, there are some risks. Recombination between an infecting plant
;RNA virus and a viral RNA inside
the engineered plant could produce
a new pathogen, and a potential
,Synergism and other interactions
could lead to new, more severe disease problems (AIBS 1995).
Today, from 75% to 100% of
agricultural crops contain some degree of host plant resistance 4
(Oldfield 1984). Most of these resistant traits in crops were added by
classical plant breeding, and they
provide enormous benefits to agriculture.
Some proponents of genetic engineering technology suggest that the
introduction of foreign crops into
the United States is a good model for
4A. Kelman, 1980, personal communication.
University of Wisconsin, Madison, WI.
October 1996
1
5
2
9
1
6
54
3
1
1
2
23
9
1
13
1
1
1
1
2
21
2
5
7
8
1
1
20
14
1
154
1992 Total
6
1
175
4
1
1
3
1
40
14
24
1
2
1
38
1
5
2
9
1
19
18
52
1
26
209
399
1
4
10
1
13
18
21
1
1
1
1
290
14
1
2
5
3
65
37
3
49
1
1
4
1
2
6
133
4
40
13
28
2
72
72
2
3
878
predicting potential effects of introduced genetic material from foreign
plant types (NAS 1987a). If so, then
there is reason for concern because
128 species of intentionally introduced crops have become serious
weeds, like Johnson grass (Pimentel
et al. 1989).
Weed control and herbicide resistance. Weeds are a major pest problem in agriculture, and both herbicides and several nonchemical
technologies are used to control
them. For example, approximately
275 million kg of herbicides are applied to US agricultural crops each
year (Pimentel et al. in press). In
addition to controlling some weeds,
herbicides can also damage crops
and increase some insect and plant
pathogen pests in the agroecosystem
(Pimentel 1995, Pimentel et al. 1992).
The use of herbicide-resistant
crops makes possible the heavy use
of herbicides without damage to the
crop. At present, breeding crops for
herbicide resistance dominates
(41 %) the field trials of genetically
engineered organisms (Tables 1 and
2; Mannion 1995). This emphasis
on herbicide resistance is indicated
by recent data on field test permits
in the United States (APHIS 1996),
which include 207 issued permits for
test releases of herbicide-tolerant
crops. The crops are tolerant to herbicidal chemicals such as glyphosate,
phosphinothricin, sulfonylurea,
bromoxynil, and 2,4-D.
In a few situations, the presence
of herbicide-resistant crops could
reduce herbicide use, provided that
farmers adopted the strategy of using only a postemergence herbicide
(i.e., one that acts after the crop
plant germinates) to control weeds
rather than both pre emergence and
postemergence herbicides (Wrubel et
al. 1992). Another option is to use a
single, broad-spectrum herbicide that
breaks down relatively rapidly instead of a persistent herbicide such
as atrazine or 2,4-D (Gressel 1992,
Krimskyand Wrubel 1993).
However, in actuality the use of
herbicide-resistant crops is likely to
increase herbicide use as well as production costs (Rissler and Mellon
1993). It is also likely to cause serious environmental problems (Pimentel et al. 1989, Schulz et al. 1990,
Tiedje et al. 1989). When a single
herbicide is used repeatedly on a
crop, the chances of herbicide resistance developing in weed populations greatly increase. Also, glyphosate, one of the herbicide substitutes
that is recommended as having potential benefits for herbicide-resistant crops, has been reported to be
toxic to some nontarget species in
the soil-both to beneficial polyphagous predators, such as spiders,
predatory mites, carabid beetles, and
coccinellid beetles, and to detritivores, such as earthworms and wood
lice (Asteraki et al. 1992, Brust 1990,
Eijsackers 1985, Hassan et al. 1988,
Mohamed et al. 1992, Springett and
Gray 1992)-as well as to aquatic
organisms, including fish (Henry et al.
1994, Wan et al. 1989, WHO 1994).
Because engineered organisms
bear alien genes that could circulate
in wild relatives, some concern has
been expressed about genetically engineered plants upsetting not only
the agroecosystem but also other ecosystems (Giampietro 1995). For ex-
667
ample, important weed species have
originated by hybridization of weedy
species with related crop plants, such
as crosses of Brassica napus {oilseed
rape} with Brassica camprestris {a
weedy relative} and of Sorghum hicolor {Sorghum corn} with Sorghum
halepense (Johnson grass; Colwell et
al. 1985, Mikkelsen et al. 1996).
However, proponents of genetic engineering rely on the experience with
corn hybrids and other genetically
altered crops that have not caused
any major environmental problems
{NAS 1987a}. Nonetheless, the basic question remains as to how to
evaluate every genetically engineered
organism before its release to ensure
its safety for the environment.
,Assessing environmental risks
To date, more than 2000 approved
releases of genetically engineered
plants have taken place worldwide
in field trials without any obvious
misadventures {OECD 1993, Whitten 1992}. However, little or no ecological research has been devoted to
determining the interaction of these
plants with their environments and
their effects on natural biota
{Krimsky 1991}. According to
Dekker and Comstock {1992}, the
emphasis has been placed on the
possible benefits rather than the potential risks. Indeed, the misconception exists that only a few ecological
questions have to be investigated
before the release of a genetically
engineered organism {Levidow 1992,
Pimentel 1995, Pimentel et al. 1989,
Wrubel et al. 1992}. This viewpoint
may hinder sound ecological assessments of genetically engineered organisms.
Monitoring protocols must be able
to identify changes in biodiversity
both in soils and above ground, thus
revealing whether genetically modified organisms have caused harm to
nontarget organisms {the United
Kingdom's Environmental Protection
Act of 1990; Levidow and Tait 1992}.
Whitten {1992} proposes several essential characteristics that genetically
engineered organisms must have if
they are to be suitable for release in
agriculture and the environment:
They should be environmentally safe,
have limited impact on nontarget
organisms, not be present in human
668
food, not cause pest resistance, and
be able to be withdrawn from the
environment if ultimately required.
In addition, the Commission of the
European Community {CEC 1990}
has described the various impacts
that genetically modified organisms
may have on an ecosystem, including enhanced primary production,
improved recycling of nutrients, and
decomposition of organic matter.
Assays of soil biota may provide
an efficient and accurate measure of
the safety and environmental impact
of genetically engineered organisms
introduced into agroecosystems. For
many years this technology has
proven effective for assessing the
potential environmental impact of
pesticides {E'dwards and Bohlen
1992, Paoletti et al. 1991}.
can be found in related wild varieties, which provide an enormous gene
pool for the development of host
plant resistance {Boulter et al. 1990}.
For example, a wild relative of tobacco that produces a single acetylated derivative of nicotine is reported
to be 1000 times more toxic to the
tobacco hornworm than is cultivated
tobacco (Jones et al. 1987). Transferring this toxic gene to nonfood
crops, such as ornamental shrubs
and trees, would protect them from
some insect pests. In addition,
thionins, proteases, lectins, and chitin
binding proteins, which are often
present in plants, especially in the
seeds, help control some pathogens
and pest insects in wild plants
(Boulter et al. 1990, Czapla and Lang
1990, Garcia-Olmedo et al. 1992,
Pimentel 1988, Raikhel et al. 1993).
Indeed, developing disease-resisAgenda for the development of
tant
crops that reduce the use of
genetic engineering
fungicides should receive high priorSome desirable areas of development ity because fruit and vegetable crops
for genetic engineering technologies are routinely treated with large
that have the potential to benefit amounts of fungicides. For example,
agricultural sustainability, the integ- on average each year US apple orrity of the natural environment, and chards receive 18 kg/ha of fungithe health and safety of society are as cides, grapes receive 29 kg/ha, and
follows:
tomatoes receive 15 kg/ha (Pimentel
et al. 1993). Fungicides are someEnhancing crop resistance to pests. times harmful to beneficial insects
Approximately 500,000 kg of pesti- and toxic to earthworms and many
cides are applied each year in US other beneficial soil biota (Edwards
agriculture, and many nontarget spe- and Bohlen 1992, Flexner et al. 1986,
cies beneficial to the environment Paoletti et al. 1988, 1991). Thenumare negatively affected. Genetic en- ber and activity of these soil biota
gineering targeted for pest control are important in maintaining soil
could diminish the need for pesti- fertility over time because they recides {Pimentel et al. 1992}.
cycle nutrients in organic matter and
Resistance factors and toxins that aid in water percolation and soil
exist in nature can be used for insect aeration (Crossley et al. 1992). Furpest and plant pathogen control thermore, the carcinogenicity of fun{Pimentel 1988}. For example, more gicides ranks the highest of all of the
than 2000 plant species are known pesticides applied to agriculture
to possess some insecticidal activity (NAS 1987b), accounting for ap{Crosby 1966}, and approximately proximately 70% of the human
700 natural substances in bacteria, health problems associated with pesfungi, and actinomycetes have fungi- ticide exposure (Culliney et al. 1993,
cidal activity {Marrone et al. 1988}. NAS 1987b).
Traits for resistance to different insect pests and diseases already exist Improving vaccines for livestock disin many cultured crops, including eases. Most data in the literature
corn, wheat, barley, soybeans, beans, support the theoretical and practical
apples, grapes, pears, tobacco, to- use of genetically modified vaccines
matoes, and potatoes {Russell 1978, against rabies (Brochier et al. 1991,
Smith 1989}.
Jenkins et al. 1991). However, the
Although some resistance charac- risk of recombination between the
teristics have been reduced or elimi- engineered vaccine virus and other
nated in commercial crops, they still orthopoxviruses endemic in wild-
BioScience Vol. 46 No.9
Table 3. What is coming to market? An update on commercialization (Gene Exchange December 1994). The chart below
summarizes agency actions on commercialization of genetically engineered products.
Product
Altered trait
Purpose
Source of new genes
Agency action
On the market?
Canola
,( oilseed rape;
Calgene)
Altered oil compositionhigh lauric acid
Expand use in
soap and food
products
California Bay, turnip
oilseed rape,bacteria, virus
USDA approved, FDA
pending, EPA not required
No
Cotton
(Calgene,
Rhone Poulenc)
Resistance to herbicide
bromoxymil
Control weeds
Bacteria, virus
USDA approved, FDA
approved, EPA pending
No
Cotton
(Monsanto)
Resistance to insects
(Bttoxin)
Control insect
pests
Bacteria
USDA pending, FDA, EPA
pending
No
Cotton
(Monsanto)
Resistance to herbicide
glyphosate
Control weed
Arabidopsis
Bacteria, virus
USDA, FDA, EPA
approved
Yes
Potato
(Monsanto)
Resistance to Colorado
potato beetle (Bt toxin)
Control insect
pests
Bacteria
USDA pending, FDA approved,
EPA pending
No
Pseudomonas
fluorescens
(Mycogen)
Toxicity to insects
(Bttoxin)
Control insect
pests
Bacteria •
USDA not required, FDA not
required, EPA approved
Yes
Increase yield in Bacteria
alfalfa
USDA not required, FDA not
required, EPA pending
No
Control weeds
Petunia, soybean,
bacteria, viruses
USDA approved, FDA approved,
EPA pending
No
Control virus
diseases
Viruses
USDA approved, FDA approved,
EPA not required
No (1995)
I
Rhizobium meNloti Enhanced nitrogen
(Research)
fixation
soybeln
(Monbnto)
Resistance to herbicide
glyphosate
Squa~h (Upjohn) Virus resistance
Tomato
- (DNA plant
research)
Delayed ripening
Enhance fresh
market value
Tomato, bacteria, virus
USDA pending, FDA approved,
EPA not required
No
Tomato
(Calgene)
Delayed ripening
Enhance fresh
market value
Tomato, bacteria, virus
USDA approved, FDA approved,
EPA not required
Yes
Tomato
(Monsanto)
Delayed ripening
Enhance fresh
market value
Bacteria
USDA approved, FDA approved,
EPA not required
No
Tomato
(Zeneca)
Thicker skin, altered
pectin
Tomato, bacteria, virus
Enhance
processing value
USDA pending, FDA approved,
EPA not required
No
Control raccoon Rabies virus
rabies epidemics
USDA pending, FDA not required,
EPA not required
No
Vaccinia virus
Immunity to rabies
vaccine
(Rhone Merieux)
life, such as cowpox virus, still needs
to be accurately investigated (Boulanger et al. 1995). The broad range
of potential vaccines for control of
various diseases is especially promising because of their low environmental risks and excellent socioeconomic benefits.
Drought resistance in crops. Approximately 5 million liters of water are
required to produce 1 ha of corn
(Pimentel et al. 1995). Thus, increas. ing drought resistance in crops would
be of great benefit (Stanhill 1991).
Given that water is vital to photosynthesis and that all crops consume
enormous amounts of water, best
October 1996
estimates are that water use in crop
production could be reduced by approximately 5%.5
Salt tolerance in crops. Traditional
agricultural systems have developed
some crop varieties resistant to salinization, for example, red rice varieties in China (Needham 1985). The
amelioration of salt intolerance is
likely to help extend the usefulness
of salinized agricultural areas, which
worldwide are increasing by approximately 1 million ha per year (Umali
1993). Projects have also been unSW. Pfitsch, 1995, personal communication.
Hamilton College, Clinton, NY.
dertaken to adapt wild plants such
as Salicornia spp., Aster tripolium,
and Crambe maritima to salinized
soils (Huiskes 1993).
Nitrogen fixation in corn, wheat,
rice, and other crops. One of the
ultimate aims of genetic engineering
is to develop cereals able to provide
their own nitrogen by bacterial symbiosis, as do leguminous plants
(Pimentel et al. 1989). If this goal
were achieved, it would reduce the
large amount of energy used to produce and apply nitrogen fertilizers
and would also reduce the costs of
production. There is growing evidence that this goal eventually might
669
be realized through genetic engineering by improving inoculation processes,
as was done in rice (You et al. 1992).
In addition, Rhizobium meliloti
is under US Environmental Protection Agency application for commercialization (Table 3). A modified version of this nitrogen-fixing
symbiotic organism is expected to
increase alfalfa production by improving nitrogen fixation in the crop
(Bosworth et al. 1994).
Development of perennial grain
crops. At present, the major cereal
crops of the world are annuals. The
conversion of annual grains to perennial grains by genetic engineering
would reduce tillage and erosion and
conserve water and nutrients (Jackson 1991). Such crops would decrease
labor costs, improve labor allocation,
and, overall, improve the sustainability
of ~griculture. Energy efficiency in
the cultivation of perennial cereal
crops would be greatly superior to
annual crops (Jackson 1991).
place (Table 3). Some consumer
groups argue that this tomato should
be labeled as genetically engineered
so that consumers can select tomatoes according to their own preferences (Verrall 1994). Appropriate
labeling of genetically engineered
food products continues to be an
important issue for many consumers. When food crops are genetically
engineered to make them brighter,
harder, larger, or modified to have
other desirable characteristics, care
must be taken not to diminish their
nutritional value.
Improving livestock ruminant nutrition. Developments in genetic engineering technology.may improve ruminant nutrition, modifying the
microbes that are involved in ruminal fermentation. The objective will
be to find suitable foreign bacterial
genes that can be inserted into ruminal bacterial organisms (Wallace 1994).
Questionable genetic
engmeermg
Improved botanical pesticides. Only
limited quantities of botanical pesti- We believe there are some questioncides are now used in developed coun- able uses of genetic engineering.
tries in place of some synthetic pesti- These uses include:
cides. However, in some developing
countries, including China and In- Bovine growth hormone (BGH) in
dia, botanical pesticides such as neem dairy cattle. Genetically engineered
are effectively used (NAS 1992). In- 'BGH increases milk production in
creasing the effectiveness of neem dairy cattle by as much as 40 % (Burand other available botanical pesti- ton et al. 1994). The US Food and
cides by genetic engineering would Drug Administration has ruled that
be an asset to farmers because they the presence of the hormone in milk
is safe for adults and children. Yet
are relatively effective and safe.
there are concerns about the impacts
Microorganisms to improve the re- of this technology on the health of
cycling of toxic wastes. Genetic modi- both cattle and humans (Broom
fications have enhanced the ability 1995). Using BGH in cattle increases
of microorganisms to digest some the chances of bacterial infections
chemical pollutants and thereby re- and mastitis and also reduces the
duce the hazards to the environment reproductive cycle in treated dairy
(Contreras et al. 1991, Krimsky cattle (Broom 1995, Burton et al.
1991). This aspect of biotechnology 1994, GAO 1992).
Millstone et al. (1994) report that
seems positive. In prerelease testing,
the interactions of such new geneti- increased infections in cattle will recally engineered organisms with non- quire treatment with antibiotics. Altarget organisms in the soil commu- though not all antibiotics appear in
nities and contaminated landscapes milk, some do. Thus, if more antibimust be carefully monitored to avoid otics are used, there might be a risk
to humans because some residues
potentially deleterious side effects.
may remain in the milk (GAO 1992).
Improving the palatability of fruits BGH treatment of cattle also raises
and vegetables. Recently a long-last- the relevant issues of bioethics of
ing, flavorful tomato was developed human health and animal welfare
and introduced into the US market- (Broom 1995).
670
Human genes introduced into livestock and crop plants. The introduction of human genes into livestock
and crop plants is being investigated
(Buttel 1988). This approach in genetic engineering appears to be unethical; if implemented, it is likely to
raise serious questions in the public's
mind about genetic engineering. Furthermore, billions of genes are available for use in genetic engineering,
so introducing human genes into livestock and crop plants for human
consumption is not necessary.
Microbes for insect biocontrol. It is
not useful to engineer organisms that
are already naturally effective biological control agents; hence, this
use should not be a priority. For
example, the nuclear polyhedrosis
virus, a highly effective biocontrol
agent for the cabbage looper, need
not be genetically engineered. The
cabbage looper can be controlled
simply by placing five infected loopers in 400 liters of water and spraying this concoction over a hectare of
crop plants. 6 Long-term human consumption and various other data have
demonstrated that consuming this
natural virus, which is highly specific for cabbage looper, is unlikely
to pose a risk to humans or other
mammals.
Release of genetically engineered
native organisms. This option could
lead to the possibility of hybridization and the development of new
plant races, including weeds. Just
because the original organism is a
native species does not mean that it
will be safe after it has been genetically engineered. Adding or deleting
a gene from a native species may
significantly alter its ecology, including the potential for increased
pathogenicity (Pimentel et al. 1989).
The safest procedure may be to
introduce an organism from the tropics and genetically alter it. Then,
once released in the northern part of
the United States or in Europe, it
would have a low probability of surviving the winters, and the possibility
of its upsetting the ecosystem would
be negated (Pimentel et al. 1989).
Toxic chemicals bred into food and
forage crops. Some toxicants, such
6D. Pimentel, 1991, unpublished manuscript.
BioScience Vol. 46 No.9
as cyanide and alkaloids, exist naturally in crop plants at relatively low
levels (Pimentel 1988). Although
these toxicants might be employed
in shrubs and trees for pest control,
genetic engineering should not be
used to add additional toxins to food
or forage crops. The known risks to
humans and other animals associ, ated with these natural toxins should
be avoided (Culliney et al. 1993).
Introducing genes into crops that
subsequently may become weeds.
Crawley et al. (1993) reported that
engineered oilseed rape is not more
invasive than its conventional coun, terpart. However, the evaluation of
genetic engineering risks for one crop
provides insufficient evidence to
judge the risks for all crops (Wilson
1990). This concern is supported by
the fact that 128 species of apparently/desirable crop plants that were
intrQ'duced intentionally into the
United States have subsequently become weed pests (Pimentel 1995).
Conclusions
Genetic engineering technology holds
exceptional promise for improving
agricultural production and keeping
it environmentally sound. Potential
benefits include higher productivity
of crops and livestock, increased pest
control and reduced pesticide use,
reduced fertilizer use by enhanced
nitrogen fixation, and improved conservation of soil and water resources.
Along with the potential benefits
for agriculture come some risks. In
essence, the release and regulation of
genetically engineered organisms into
the environment should be similar to
the release and regulation of exotic
plant and animal species into a new
environment (Pimentel et al. 1989).
Therefore, time and effort must
be devoted to laboratory and field
testing before the release of genetically engineered organisms. Without
caution and suitable regulation, environmental problems are likely to
arise and the expected benefits of
genetic engineering are likely to be
jeopardized.
Acknowledgments
We are indebted to the following
persons for discussions, suggestions,
October 1996
(DC): National Academic Press.
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