Biology Reference
In-Depth Information
free environment. In the case of the diamondback moth (
Plutella
xylostella
), however, resistance in some populations does not appear to
reduce fitness, and the protein endotoxin itself may be metabolized with
benefit to the moth larva (Sayyed et al. 2003).
For Bt maize, a strategy to delay the evolution of resistance by insect
pests has been to couple plantings of Bt maize with refuge plantings of
susceptible maize. Although selection for resistance might be high in
fields of Bt maize, the high production of insects without resistance in
refuges would delay the spread of resistance genes in the insect popula-
tion at large (Alstad and Andow 1995). Unfortunately, the level of com-
pliance to this strategy by farmers is far from complete (Dale et al. 2002).
Regulatory Issues
The technology of genetic engineering is tending to evolve more rapidly
than regulatory capability. At present, evaluation of potential risks is based
on short-term evidence that cannot evaluate the long-term potential for
reorganization of genomes of wild organisms into which transgenes have
escaped. The situation in this regard is similar to that of introduced alien
species, in which only a fraction of those that become established become
serious problem species. As Williamson (1993) noted, the fraction of
genetically modified organisms that lead to problems is likely to be small,
but the impacts of those that do could potentially be very serious.
Regulatory procedures have not adequately come to grips with the
complexity of the genetic manipulations that are being performed. Intro-
ducing a specific gene into a specific organism, for example, may result in
multiple transgenic lines that have different biological properties (Bergel-
son and Purrington 2002). Regulatory requirements for risk assessment
are also far from adequate. Requirements for replication and duration of
tests for nontarget impacts of plants carrying the Bt endotoxin transgene
are inadequate to detect real effects in most cases (Marvier 2002). Fur-
thermore, the required laboratory testing does not come to grips with the
complexity and variability of conditions that exist in the open ecological
systems into which these plants would be introduced.
Future Trends in Genetic Engineering
The potential of genetic engineering to modify the genetic structure of
plants, animals, and microorganisms has only begun to be realized, as have
the risks of spread of transgenes to nontarget organisms. The diversity of
