be genetically engineered for resistance to insecticides, thereby allowing simultaneous use of both biologic control mechanisms (Braig and Yan, 2002).
Another means of biocontrol is the release of sterile males. Unfortunately, such programs are expensive and might require the release of sterile females where the insects cannot be sexed before release. Techniques used to induce sterility, such as irradiation, often render the insect noncompetitive as a potential mate. A possible solution to these problems is to genetically engineer the insect to allow either genetic sexing, for example, through a female lethal gene, or through direct production of sterile males. Finally, GE insects can be developed to produce visual markers, such as green fluorescent protein (GFP), to determine the effectiveness of sterile release programs (Braig and Yan, 2002).
Another application of transgenesis is to control transmission of diseases by such vector organisms as mosquitoes. With GE technology, it might be possible to disrupt an insect’s ability to carry and transmit diseases such as Plasmodium, the malaria parasite (Braig and Yan, 2002; Spielman et al., 2002; Ito et al., 2002). An environmental concern is presented because the parasite has a negative effect on the fitness of the mosquito (Braig and Yan, 2002; Spielman et al., 2002). Elimination of the parasite could result in the release of mosquitoes from a form of biocontrol, with a possible associated increase in mosquito populations. An increase in mosquitoes also could lead to increased spread of other mosquito-borne diseases to both animals and humans.
The development of molecular methods for genetic engineering of terrestrial arthropods (reviewed by Atkinson et al., 2001; Handler, 2001) has not been matched by advances in understanding how to deploy GE arthropods in practical pest management, or of how to evaluate potential harms associated with their release into the environment (Spielman, 1994; Hoy, 1995; 2000; Ashburner et al., 1998). Key issues pertaining to environmental risk (Hoy, 2000) include the possibility that transgenic insects released into the environment would pose unknown ecologic impacts, and that gene constructs inserted into insects could be transferred horizontally through known or unknown mechanisms to other species, thereby creating new pests.
If a genetically engineered arthropod is to be released within a practical pest management program, any potential ecologic risks associated with its release into the environment must be assessed, although guidelines for conducting such an assessment do not yet exist (Hoy, 1992a; 1992b; 1995). Anticipation of ecologic risks will depend upon predictions of the impact of changed abundance or dynamics of the engineered species upon resources or species with which the organism interacts in the environment, including predators, prey, competitors, and hosts.
Further, the methods by which horizontal gene transfer (Chapter 2) could occur should be investigated so that it can be determined whether and how to assess this particular hazard (Hoy, 2000). Should horizontal transfer of a transgene be demonstrated, it poses significant effects for the evolution of a