released into the environment is of high concern, both from biological and legal/regulatory standpoints.
L. LaReesa Wolfenbarger (University of Nebraska, Omaha) framed consideration of the environmental effects of GE crops by looking at research in three, interrelated categories: the impacts of GE crops on wildlife food (insects eaten by birds and other animals) in farm fields and adjacent land; impacts on wildlife in farm fields; and impacts on wildlife in land adjacent to farm fields, such as grassland, forests, riparian areas, wetlands, or streams.
According to Wolfenbarger, most relevant studies have focused on the abundance of wildlife food, particularly non-target and beneficial arthropods, in the presence or absence of a GE crop. Although the basic research question is whether and how GE crops impact the abundance of wildlife food, she noted that an important factor to emerge was the background effects of different agricultural practices. For example, a meta-analysis by Marvier at al. (2007) showed decreases in the abundance of non-target insects of the orders Coleoptera, Hemipteran, Hymenopterans and particularly Lepidoptera in fields planted with transgenic cotton expressing Bacillus thuringiensis (Bt) proteins relative to non-transgenic cotton. However, the abundance of all insects were much lower in fields planted with cotton crops (transgenic or not) sprayed with insecticide. A key finding of the study was that one’s view of what is ecologically beneficial depends on the points of comparison. About 80 percent of cotton acreage in the United States is sprayed with insecticides, said Wolfenbarger.
Similarly, results of a comparison of the effects of Bt-corn on wildlife food depended on whether it was compared with insecticide-sprayed or nonsprayed corn and the types of insecticide (Wolfenbarger et al., 2008); currently, she said, about 25 percent of the U.S. corn crop (75 percent of sweet corn) is treated with insecticide. Finally, Cattaneo et al. (2006) looked at the impact of Bt-cotton and other agronomic practices on the diversity of wildlife food in farm fields relative to the diversity in adjacent habitat, using the adjacent, uncultivated area as the baseline. They found that relative to uncultivated areas, cotton cultivation had a negative impact on ant density and a positive impact on beetle density, but those findings were irrespective of whether the crops grown were or were not transgenic.
The conclusion Wolfenbarger drew from these studies was that GE