Biology Reference
In-Depth Information
Because this predatory mite lacks wings and tends to stay on plants if provided adequate prey, the
transgenic predators were released into the center row of potted plants with the outside row of pesticide-
treated plants serving as “traps” to reduce the likelihood of escape from the plot (
Figure 14.2A
). The white
poles surrounding the release site contain clear sticky panels (not visible) at two heights to monitor any
movement of the predators out of the plot; only two to three predators were collected on the sticky panels
over the course of the experiment. At the end of the experiment, the plants were placed in plastic garbage
bags and autoclaved to preclude the transgenic predators from persisting in the environment.
The short-term release was conducted in 1996 after permission was obtained from USDA-APHIS, the
University of Florida's Biosafety Committee, the Florida Department of Agriculture and Consumer Services,
the Florida Department of the Environment, and the U.S. Fish and Wildlife Service. Personnel from these
agencies were present at the release site to ensure that the requirements of the permit were met (
Figure
14.2B
). The goals were to determine the stability of the transgenic line, demonstrate that we could contain
the predator in the release site, and retrieve the predators at the end of the experiment.
Despite the stability of Line 18 for
>
200 generations in the laboratory, we discovered that there was a
fitness cost and the
lacZ
construct was unstable under field conditions, for unknown reasons. The construct
was lost from the strain within six generations, possibly due to DNA-repair mechanisms. This disappointing
result demonstrates why short-term field evaluations are necessary before transgenic arthropods can be
deployed in pest-management programs (Hoy 2000).
Box 14.2 Releases of Sterile Transgenic Pink Bollworms in the United States
Containing Fluorescent Marker Genes
The pink bollworm (PBW),
Pectinophora gossypiella
, became a significant pest of cotton in the southwestern
United States after its invasion into North America in 1911. Efforts to control this lepidopteran pest have
included the use of pesticides, the SIT, planting of
Bacillus thuringiensis
(
Bt
) transgenic cotton, cultural
practices (shredding of diapausing larvae during the winter in cotton residues), and mating disruption with
the PBW sex pheromone. Area-wide suppression of the PBW using these methods has resulted in population
suppression. However, the PBW has been estimated to cost at least US$32 million per year due to control
costs. As a result, the National Cotton Council proposed to eradicate the PBW by using all of these control
methods (
Grefenstette et al. 2009
). Improving the SIT program directed against the PBW is an important
component. One of the improvements would be to improve the discrimination between released marked
sterile male moths and wild males in the sex-pheromone traps. Marking of released sterile moths has relied
on a red dye added to the larval diet, which results in moth tissues becoming red. However, the moths can
excrete all of the dye and the dye can be lost from the moths in the field, making it difficult to provide an
accurate estimate of the PBW population density. It would be desirable to have a permanent marker that
allows program managers to reliably identify released and wild males. “If a fraction of these wild captures
are actually misidentified sterile moths, due to marker failure, such releases are a waste of resources”
(
Walters et al. 2012
). Furthermore, because released sterile moths are irradiated with substerilizing doses to
minimize damage from irradiation, F
1
progeny are produced, although they are sterile (F
1
sterility). Accurate
identification of these sterile F
1
moths is also important to monitoring the progress of the SIT program
because these adults are not marked with dye, but these sterile F
1
males will not have been marked.
The first effort to improve the marking system was made by transforming the PBW with an enhanced
green fluorescent protein (EGFP) gene regulated by an
actin
promoter using the
piggyBac
vector (
Peloquin
and Miller 2000, Peloquin et al. 2000a, Miller et al. 2001
). A permit was given by the U.S. Department of
Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) to release the transgenic strain in
January 2001 and an Environmental Assessment was provided. Releases were made after the strain had been
