POTENTIAL RISKS OF TRANSGENIC ARTHROPOD BIOLOGICAL CONTROL AGENTS
Marjorie A. Hoy
Department of Entomology and Nematology, PO Box 110620, University of Florida, Gainesville, FL 32611-0620
Key words: transgenic arthropods, risk analysis, biological control, agriculture, environmental releases
INTRODUCTION
Transgenic pest and beneficial arthropods are being developed for pest management programs (Hoy, 1994) .
Methods for producing transgenic arthropods are available and projects to deploy them in pest management programs have been proposed. In most cases, deployment would require the permanent establishment of the transgenic arthropod in the environment.
Genetic manipulation of predators and parasitoids of agricultural pests could result in improved biological control and reduced pesticide use. However, before any transgenic arthropod can be released, risk analyses must be conducted. In November 1993 a workshop was held in Gainesville, Florida to discuss potential risks associated with releases of transgenic predators and parasitoids of insect and mite pests. The conclusions are summarized here.
Several general issues were discussed in some depth: For example, the risks of horizontal transfer of transgenes from the arthropod natural enemy to other organisms. Hugh Robertson described the role of transposable elements such as mariner in horizontal transfer. Several significant conclusions were made:
Horizontal transfer is a rare event on a human time scale.
The risks of horizontal transfer of exogenous DNA should not be different than the risks of horizontal transfer of endogenous DNA if disabled transposable element vectors are used.
Horizontal transfer probably is a source of genetic variability in evolution, and is thus a natural process (Kidwell 1992).
Another issue: Are there unique aspects of releasing transgenic beneficial arthropods as compared to plants or microbes? The conclusion reached was that, from an ecological viewpoint, arthropods are different because they have multiple trophic relationships within their communities. This is less true for plants or microorganisms.
Another conclusion was that releases of transgenic arthropod natural enemies should be a two-step process. The group rejected a one-step process. While plants and microorganisms have been released many times experimentally, and no environmental harm has been documented, it is prudent to release transgenic beneficial arthropods in a two-step process:
1. Experimental small plot releases
2. Permanent releases only after extensive testing
Furthermore, the group concluded that the scientific considerations discussed by the Ecological Society of America (Tiedje et al., 1989) and the ABRAC (1992) generally are useful in considering the potential risks associated with releases of transgenic arthropod natural enemies.
Some concerns in the Ecological Society of America list were rejected or amended as not fully comparable or not relevant:
Trophic level relationships in arthropods are more complex than they are for microbes or plants.
The arthropod genome is 'intrinsically stable', compared with more highly mutable genomes such as RNA viruses.
The ability to incorporate exogenous DNA by various mechanisms probably is a general phenomenon.
Active transposable elements probably are present in all arthropods
The following four components of risk analysis were discussed, and were reworded to make them more relevant to discussions of arthropod natural enemies.
Attributes of Unmodified Organism
Origin (indigenous or nonindigenous in the accessible environment)
Trophic level and host range
Ease of control and monitoring
Survival in the environment
Dissemination in the accessible environment
Potential of gene exchange with other populations
Other ecological relationships
Is the arthropod involved in basic ecosystem processes ?
Genetic Attributes of Alteration
Intent of genetic alteration
Nature and function of alteration
Vector source and type, if employed
How well characterized is the genetic modification ?
Degree of genetic stability
Phenotype of Modified Organism Compared to Unmodified Organism
Host/prey range
Fitness and effectiveness
Expression of the trait
Susceptibility to control by natural or artificial means
Environmental limits to growth or reproduction (habitat, microhabitat)
Similar to phenotypes previously used
Attributes of the Accessible Environment
Describe accessible environment
Alternate hosts or prey
Wild relatives within dispersal capability of organism
Relationship to potential geographic range
Are endangered/threatened species likely to be affected ?
Will there be selection for the engineered trait ?
Are there vectors or agents of indirect dissemination ?
Do the test conditions provide a realistic simulation to nature ?
Degree of public access to test site
Effectiveness of monitoring and mitigation plans
Finally, the procedural issue of how a person would obtain permission to make a release of a transgenic arthropod natural enemy was discussed extensively. Most academic scientists were confused and dismayed by the diversity of agencies and lack of clear guidelines on what is permitted and what is not.
This conference provided some answers to the question: What agencies should be consulted by a scientist and when? The following agencies should be consulted, preferably as early as possible:
USDA-APHIS, BBEP
University biosafety committees, if appropriate
State regulatory officials
Fish and Wildlife regarding threatened and endangered species
However, there are no specific forms to be filled out because each application is considered on a 'case-by-case' basis. Most of the academic scientists present expressed general frustration with this approach, and argued that scientific principles should be used to develop a general consensus on risk assessment methods appropriate for releases of transgenic arthropod natural enemies. Figure 1 describes the relationship between risk assessment issues for transgenic arthropods.
ACKNOWLEDGMENTS
I thank the participants of the Gainesville workshop for their contributions.
REFERENCES
ABRAC. 1992. Guidelines for Research Involving Planned Introduction into the Environment of Genetically Modified Organisms. Guidelines recommended to USDA by the Agricultural Biotechnology Research Advisory Committee, 3-4 December 1991. USDA Office of Agricultural Biotechnology Document No. 91-04: 20 pp. + Appendix.
Kidwell, MG (1992) Horizontal transfer. Curr. Opin. Genet. Develop. 2: 868-873.
Tiedje, J M, Colwell, RK, Grossman, YL, Hodson, RE, Lenski, RE, Mack, RN and Regal, PJ (1989) The planned introduction of genetically engineered organisms: Ecological considerations and recommendations. Ecology 70: 298-315.
Hoy, MA (1994) Insect Molecular Genetics: An Introduction to Principles and Applications. Academic Press, San Diego.
Hoy, MA (1995) Impact of risk analyses on pest management programs employing transgenic arthropods. Parasitology Today 11(6): 229-232.
Figure 1. Risk assessment issues influence the steps employed in developing transgenic pest or beneficial arthropods for pest management programs. Risk assessment issues should be considered early in the project, as well as prior to evaluation in the field (Hoy, 1995).