Biology Reference
In-Depth Information
transcriptional activator [tTAV]) (
Phuc et al. 2007
). In the absence of tetracycline, the tTAV binds to a
minimal promoter and drives expression of more tTAV in a positive feedback loop, resulting in low-level
expression. When tetracycline is present, tTAV binds tetracycline, which does not bind to the binding site
and does not lead to expression of more tTAV. High-level expression of tTAV is toxic, so its expression
provides a tetracycline-repressible lethal system (Phuc et al. 2010). The exact mechanism of toxicity is
unknown. The tTAV construct is repressed during mass rearing in the presence of tetracycline, but is active
in the field when tetracycline is lacking.
The first release of transgenic
Ae. aegypti
containing a RIDL construct took place in the Cayman Islands
in fall 2009. Releases by the Oxitec company were not announced until November of 2010, which
created concerns about a lack of transparency (
Enserink 2010b
). A subsequent release was made the
following summer. The Cayman Islands apparently lacked a biosafety law at the time of the releases, but
the Mosquito Research and Control Unit of the Cayman approved the releases. However, there were no
town hall meetings or public debates prior to the releases and, although information was sent to local
newspapers, Enserink (2010) reported there was no mention that the mosquitoes were transgenic, so
informed consent by the inhabitants was not obtained.
Harris et al. (2011)
reported the results of releasing the RIDL mosquitoes into 10 hectares of the
Cayman Islands. They indicated that the 465 male mosquitoes released per hectare per week over a four-
week period mated with wild females and fertilized their eggs, based on analysis of eggs that hatched
and produced fluorescent larvae. 126 fluorescent larvae were found in the egg traps, which was 9.6% of
the 1316 larvae found. PCR analysis of DNA from trapped males indicated there were 20 released males
and 105 wild males, or the RIDL males comprised
≈
16% of the total males trapped during this period,
assuming equal trapping efficiency. No information was provided as to the persistence of the released
mosquitoes after the trial concluded, or whether dengue transmission was affected. It is known that up
to 15% of RIDL mosquito progeny may survive and it is also known that some environments contain
tetracycline, an antibiotic that is widely used in medicine, and for veterinary and livestock purposes, and
can be found in wastewater and sewage. The Oxitec website claims that environmental levels of tetracycline
are too low to allow survival of the transgenic mosquitoes, but it is not clear if that is always true.
Subbaraman (2011)
, a reporter for
Nature Biotechnology
, reported that some environmentalists are
worried, “that transgenic insect releases that reduce wild mosquito numbers might not only create an
'empty niche', which other potentially damaging insects might fill, but also affect organisms higher in the
food chain that rely on mosquitoes as a dietary source.”
Subbaraman (2011)
reported, “
…
the company
liberated about 3.3 million sterile male transgenic
Aedes aegypti
mosquitoes into a region spanning about
16 hectares through 80 releases,” results which were not included in the report by
Harris et al. (2011)
.
Subbaraman (2011)
reported on a presentation at a scientific meeting by Luke Alphey of Oxitec that,
“
…
results from the large release showed up to an 80% reduction in the numbers of wild mosquitoes
~11 weeks after the release. This reduction in the population was sustained for a further ~7 weeks.” It is
not clear whether there was a control for this experiment or if dengue transmission was affected. Nor is it
clear that informed consent was obtained from the local inhabitants.
Releases of
Ae. aegypti
containing the RIDL construct were made in Malaysia during 2010-2011 and in
Brazil in 2011 and 2012.
Lacroix et al. (2012)
reported on the release of fluorescent powder-marked RIDL
and wild-type male mosquitoes into the field near Bentong in Malaysia during December 2010. Males
were to be captured in adult traps up to 96 or 328 m away, and eggs were to be evaluated from ovitraps.
Lacroix et al. (2012)
reported that 50% of the RIDL mosquitoes and 17% of the wild-type mosquitoes
were recaptured. The last recaptures were made on days 9 and 12 for the two strains, indicating that
the transgenic males survived well in the field. The ovitraps had no fluorescent larvae, indicating that no
mating occurred between the RIDL males and wild females,
or
that the mated females failed to deposit
eggs in the ovitraps. According to the Malaysian website, no recaptures were obtained after 3-5 January,
