Transgenic Insecticidal Corn:
Beyond Insecticidal Toxicity to Ecological Complexity
Date: 8 Jul 2001 10:19:17 -0500
From: joe cummins <jcummins@uwo.ca>
Subject: last word on Bt corn
The article below is the last word from the researchers on Monarch and Bt corn. The conclusion is clear that the Bt corn is not effective. The
StarLink fiasco was fall out from an ineffective product.
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Transgenic Insecticidal Corn:
Beyond Insecticidal Toxicity to Ecological Complexity
JOHN J. OBRYCKI, JOHN E. LOSEY, ORLEY R. TAYLOR, AND LAURA C. H. JESSE
358 BioScience . May 2001 / Vol. 51 No. 5
Conclusions and recommendations
Unlike the use of transgenic potatoes and cotton, the use
of transgenic corn will not significantly reduce insecticide use in most of the
corn-growing areas of the Midwest. During the past 5 years, the percentage of
field corn treated with insecticides in the United States has remained at
approximately 30%, despite a significant increase in the hectares of Bt corn
planted (Figure 2).From 1995 to 1998, about 1% to 2% of the corn grown in
Iowa--where over 4 million hectares of corn are grown annually--was treated with
insecticides for O. nubilalis (Figure 3).A survey of veteran corn farmers in
Iowa and Minnesota--the average farming career was 21 years--showed that 70% had
never used insecticides for the first generation of the corn borer, and 82.7%
had never treated for the second generation (Rice and Ostlie 1997).Approximately
5% had used insecticides three or more times in 21 years to manage the corn
borer.
Despite the relatively low use of insecticides during the
1990s for corn borer suppression, between 20% and 30% of the corn planted in the
United States in 1998 and 1999 was transgenic (Fernandez-Cornejo and McBride
2000), suggesting that the Bt plantings are not being used as a replacement for
insecticides but in addition to them. A core concept of integrated pest
management is to use a management tactic only when pest populations exceed a
threshold level. It seems, then, that the hectares planted in Bt corn represent
a change in approach from management of O. nubilalis to a prophylactic strategy.
Because population densities of the European corn borer are
unpredictable, the economic benefits of using transgenic corn are not assured
(Rice and Pilcher 1998,Hyde et al. 1999, Archer et al. 2000).Comparisons of
yields from transgenic and genetically similar nontransgenic corn hybrids grown
in replicated plots in 14 to 16 locations in Iowa (Farnham and Pilcher 1998,
Rice 1998) showed that only 34% of the transgenic lines produced significantly
higher yields in 1997. In locations where corn borer damage was highest in
nontransgenic lines, 50% to 58% of the transgenic hybrids produced significantly
higher yields. In 1998, when corn-borer densities were generally lower than
usual in Iowa, 12% of transgenic lines produced significantly higher yields.
Further analysis of these comparative data shows a weak
relationship (r2 = 0.13) between the amount of insect damage and increased
yields in the Bt corn in 1997 and no relationship in 1998. Analysis of a second
data set collected for the USDA National Agricultural Statistics Survey in 1998
showed no economic benefit of transgenic insecticidal corn in Iowa (Duffy and
Ernst 1999), probably because of differences in the amount of fertilizer applied
to the Bt and non-Bt fields. Previous assessments of Bt corn have indicated that
the economic benefits of this technology are highly dependent on the population
densities of the corn borer and the market value of field corn (Rice and Pilcher
1998). From 1997 to 1999, corn borer densities were generally low in Iowa and
the value of field corn had declined. Thus, in these 3 years the economic
benefits of Bt corn were not consistently demonstrated.
Given the limited benefits for insect management and the
documented ecological effects of transgenic insecticidal corn on nontarget
species,we conclude that this biotechnology has a limited role in management of
lepidopteran pests in corn. The use of transgenic crops has been promoted as
safer for humans and the environment than use of broad-spectrum insecticides (Pimentel
and Raven 2000). However, most field corn in the US corn belt is not treated for
above-ground insect pests, and most corn hybrids already have substantial
resistance to corn borers (Barry and Darrah 1991).
The approach taken in the registration of transgenic corn
and in its current use in pest management has been narrowly focused on
insecticidal toxicity, but we believe that a more comprehensive approach is
required (see, e.g., Stern et al. 1959, Lewis et al. 1997), one that considers
the ecological complexity of agroecosystems (Figure 1b).We have outlined in this
article the potential benefits and ecological risks of the use of Bt corn. These
potential risks are not thoroughly addressed in the US governmental registration
process, an oversight that should be attended to.
The widespread and unquestioned acceptance of Bt corn by
the agricultural research, regulatory, and educational communities is similar to
the rapid adoption and deployment of synthetic insecticides in the early
1950s.During that time ecologically based management programs suffered, and
predicted adverse ecological and environmental effects were generally ignored,
resulting in limited management options for farmers as targeted species
developed resistance and nontarget predator and parasitoid species declined.We
are not advocating the elimination of Bt corn, nor do we discount the potential
benefits of biotechnology for agriculture.We do argue, however, that a balanced
examination of Bt corn suggests ways to improve the regulatory process and to
incorporate this technology into an integrated control framework, and we caution
against the acceptance of yet another silver bullet for pest management.
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