species, introducing otherwise unavailable genetic material to the genome of a species (Droge et al., 1998). Horizontal gene transfer would pose no harm if the gene that is moved were lost, inactivated, or benign. However, if horizontal gene transfer confers increased fitness, perhaps by establishing the dominant, selectable antibiotic or pesticide resistance trait used in the production of the transgenic arthropod, then harm could be realized. Risk posed is not dependent solely on the frequency of transfer. Even rare events might cause ecologic impacts if the transferred gene increases the fitness of the recipient (Droge et al., 1998).

Considerable progress has been made in the development of methods for genetic engineering of the mosquito germ line and in identification of parasite-inhibiting molecules (Beernsten et al., 2000; Blair et al., 2000). Despite the technical progress, there remain important scientific questions that must be addressed prior to a program releasing GE mosquitoes (Braig and Yan, 2002; Spielman et al., 2002). Can parasite-inhibiting gene constructs indeed spread and become fixed in wild mosquito populations? In order to do so, a driver mechanism will have to be developed that would cause a disproportionate frequency of offspring of the released mosquitoes to carry the introduced construct (Braig and Yan, 2002; Spielman et al., 2002). Such driver mechanisms might include competitive displacement, meiotic drive (Sandler and Novitski, 1957), biased gene conversion, and others (Braig and Yan, 2002). The fate of parasite-inhibiting genes would be determined not only by the mechanism used to drive the fixation of the genes, but also by the magnitude of any loss of fitness in the host, and also by a range of ecologic and abiotic environmental factors. Possible human health effects posed by genetic engineering of disease vector insects are discussed in Chapter 3.

In the context of environmental concerns posed by GE arthropods, it is clear that purposeful release of transgenic arthropods will depend upon prior risk assessment and risk management. Hoy (1997) called for effective containment of transgenic arthropods in the laboratory and thorough peer review by scientists and regulatory agencies prior to any field release. However, there are no U.S. or international guidelines for containment of transgenic arthropods. Additionally, there are no proven techniques for retrieving transgenic insects after environmental release should they perform in unexpected ways.

Fish and Shellfish

Considerable research effort has been devoted to development of GE fish and shellfish stocks, as they pose considerable benefits to producers (Chapter 1). Production of some GE fish or shellfish could result in environmental benefits. For example, expression of growth hormone transgenes has been shown to increase feed conversion efficiency (Cook et al., 2000; Fletcher et al., 2000),



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