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Abstract: The use of genetic engineering and biotechnology in agriculture has attracted worldwide attention over the past decade. This technology has raised highly controversial issues and considerable international debate over [...]

Corn (Zea mays L.) that has been genetically engineered to produce the Cry1Ab protein (Bt corn) is resistant to lepidopteran pests. Bt corn is widely planted in the midwestern United States, often adjacent to headwater streams. We show that corn byproducts, such as pollen and detritus, enter headwater streams and are subject to storage, consumption, and transport to downstream water bodies. Laboratory feeding trials showed that consumption of Bt corn byproducts reduced growth and increased mortality of nontarget stream insects. Stream insects are important prey for aquatic and riparian predators, and widespread planting of Bt crops has unexpected ecosystem-scale consequences. caddisflies | genetically modified crops

A vast literature has accumulated since crop varieties with transgenic resistance to insects and herbicide tolerance were released to farmers in 1996 and 1997. A comparatively minor segment of this literature consists of studies conducted by agricultural economists to measure the farm-level impact of transgenic crop varieties, the size and distribution of the economic benefits from adopting them and the implications for international trade. This paper focuses only on the applied economics literature about the impact of transgenic crop varieties in non-industrialised agricultural systems, with a focus on the methods. A number of studies have surveyed the findings for both industrialised and non-industrialised agriculture at various points in time, but surveys of methods are less common and most treat one aspect of economic impact. Clearly, the methods used in research influence the findings that are presented and what they mean. Three levels of impact analysis are considered: farm, industry and trade. We conclude that because the methods used present challenges and limitations, the few transgenic crop-trait combinations released in developing economies and the relatively brief time frame of most analyses, the results are promising but the balance sheet is mixed. Thus, the findings of current case studies should not be generalised to other locations, crops and traits.