Environmental Safety of Genetically Engineered Crops

Evaluation of Potential Impacts of Genetically Engineered Plant-Incorporated Protectants on Non-Target Organisms

87 Evaluation of Potential Impacts of Genetically Engineered Plant-­Incorporated Protectants on Non-­Target Organisms Robyn Rose Agricultural biotechnology has fundamentally changed the way crops can be genetically modified to provide resistance to pests. Genetically engineered (GE) crops that express insect-­ pest resistance traits could facilitate a shift away from the reliance on broad-­ spectrum insecticides and toward biological-­ based pest management. Like any insect control technology, GE crops may present a risk to beneficial insects such as the natural enemy community , pollinators, and organisms involved in decomposition and nutrient cycling. The use of insect-­ resistant plants is not equally appropriate for all crops in all agricultural systems. Therefore, a case-­ by-­ case scientific analysis of risks and benefits should be conducted before commercial use. Transgenic plants that produce insecticidal substances are and should continue to be subject to careful testing to ensure safety and minimize environmental risks. A tiered approach to an ecological risk assessment is recommended, particularly in a regulatory context, as a screening tool to determine potential risks to non-­ target organisms from releasing a GE crop in the environment. Non-­ target organisms consist of invertebrates beneficial to maintaining a healthy ecosystem in an agricultural setting such as pollinators (e.g., honey bees), biological control organisms (e.g., predators and parasitoids) and decomposers (e.g., earthworms and Collembola). Other wildlife that are not intended to be harmed by a GE crop such as birds, mammals, and fish are also considered non-­ target organisms. A tiered approach allows for a common testing framework and a standardized sequence of tests to be used as screening tools to evaluate and focus risk considerations. Although an acute dietary laboratory test may indicate no acute adverse effects on non-­ target organisms, there are many pathways to consider by which GE crops can interact both directly and indirectly with target and non-­ target organisms at different trophic levels within the crop system, as well as in habitats outside the crop in the surrounding landscape; therefore, higher-­ tier field and semifield tests are often required for GE crops. Potential risks should be assessed in a field experiment large enough to represent real-­ world conditions and involve a broad taxonomic range of organisms at the community level. This chapter focuses on GE plants containing insecticidal proteins because of the potential for ecological consequences and because these crops are the most extensively grown and 88| Robyn Rose studied GE crops to date. Many direct and indirect effects could result from the release of a GE crop in the environment, such as a fitness costs to an organisms (e.g., reduced growth or reproductive rates), a reduction in the abundance or diversity of non-­ target organisms , or a reduction in functional responses (e.g., ability to parasitize a host or decompose plant material). GE Plants Expressing Insecticidal Proteins Since the early 1990s, many biotech companies and public institutions have invested considerable research and development in transgenic crops resistant to insect pests. Currently, only insect-­ resistant plants expressing genes from Bacillus thuringiensis (Bt) are available for commercial use. Bt is an ubiquitous gram-­ positive, spore-­ forming bacteria found in many environments including soil, insects, stored-­ product dust, and deciduous and coniferous leaves. The bacterium forms a parasporal crystal during the stationary phase of its growth that results in its insecticidal activity. The crystals are made of protoxins, referred to as Cry toxins or endotoxins, which, when ingested by an insect, are activated by proteases in the insect midgut (Schnepf et al. 1998; Gill et al. 1992). Cry toxins readily bind to receptors on the apical brush border of the midgut microvillae of susceptible insects and insert into the membrane. This insertion leads to the formation of pores causing lysis of cells, leading to starvation, paralysis, septicemia, and death of the insect (Schnepf et al. 1998). Bt toxins have been used for more than 30 years in bioinsecticide formulations. However, their use in commercial agriculture has been limited because of their short residual action, narrow spectrum of activity, and specific route of entry, which requires ingestion. The genetic engineering of plants that express Cry proteins constitutively in all tissues and continuously throughout the growing season has overcome many of the limitations of Bt microbial insecticides . In some instances, transgenic delivery of Cry proteins has resulted in fewer insecticide applications and thus lower management costs (Schnepf et al. 1998; EPA 2001; Brookes and Barfoot 2005; Fitt 2008; Qaim et al. 2008). In addition, one notable advantage to using transgenic insecticidal...