Biology Reference
In-Depth Information
females transmitted
Wolbachia
at a high rate, and the hatch rate of eggs in the incompatible crosses was
<
1%.
Even when infected mosquitoes were reared under low food levels and high densities, they still maintained
their decreased longevity and CI levels. Infected lines had a reduced egg hatch rate at different temperatures.
These laboratory data provided “parameter estimates for predicting invasion by a
Wolbachia
infection for
dengue suppression when placed on an outbred background. Outbreeding ensures that release material has
a genetic background that matches the target population. Our parameter estimates suggest that
w
MelPop
invasion is possible under humid conditions. However, because of deleterious effects associated with
w
MelPop-CLA, invasion under dry conditions will be difficult
…
” (
Yeap et al. 2011
). The group subsequently
developed another line of mosquitoes infected with a different strain of
Wolbachia
.
Walker et al. (2011)
adapted the
w
Mel strain of
Wolbachia
from
D. melanogaster
in
Ae. aegypti
cell culture
over 2 years. Stably infected
Ae. aegypti
lines were generated by microinjection into embryos. An outbred
line was established by crossing an infected laboratory population with wild-caught mosquitoes. The
out-crossed strain induced strong cytoplasmic incompatibility and fitness was not significantly different
to that of uninfected mosquitoes under semifield conditions.
Walker et al. (2011)
next showed that the
w
Mel strain of
Wolbachia
blocked dengue transmission and, under semifield conditions, increased from a
starting frequency of 0.65 to near fixation within a few generations, invading
Ae. aegypti
populations at an
accelerated rate relative to trials with the
w
MelPop-CLA strain.
Two towns in Queensland were selected to test the release of mosquitoes infected with
Wolbachia
(
Enserink 2010a
). In the field trial, mosquitoes were released weekly for 12 weeks, with the goal of
determining how well the
Wolbachia
-infected mosquitoes are able to spread the
Wolbachia
into the wild
population. Clear regulatory authority to evaluate these releases was not present, but the releases were
conducted after the Commonwealth Scientific and Industrial Research Organization (
CSIRO 2010
)
conducted a risk analysis and concluded “negligible risk” that infected mosquitoes would cause harm. The
Australian Pesticides and Veterinary Medicines Authority also evaluated the proposed releases.
Hoffmann
et al. (2011)
reported the results of the releases into two sites near Cairns, Australia. Prior to releases,
water was removed from breeding containers in the vicinity of the homes, and in early January 2011 adults
(both males and females) were released at 184 and 190 locations at each site, followed by nine releases
over the following 9-10 weeks for a total of 141,600 and 157,300 adults, respectively. Mosquitoes were
monitored for
Wolbachia
infection every two weeks and the infection frequency increased to
>
15% in both
sites within 2 weeks after release. In one site, the infection frequency reached near fixation five weeks
after releases were terminated and reached 90% at the same time interval in the second site. Analysis
suggested that fitness costs caused by the
Wolbachia
infection could be
≈
20% in the field (
Hoffmann et al.
2011
). The authors did not evaluate the role of these infected mosquitoes in transmission of dengue
but, “demonstrated that it is possible to produce
Wolbachia
-infected mosquito populations that can
act as 'nursery' areas for future human-assisted collection and further dispersal of
Wolbachia
-infected
mosquitoes, without the need to rear additional mosquitoes in an insectary. This should provide a
strategy for sustainable dengue control at low cost, with a relatively simple deployment system suitable for
implementation in developing countries.” Additional releases of
Wolbachia
-infected
Ae. aegypti
in Australia
were conducted in 2012 using the
w
MelPop-CLA strain (
Cyranoski 2012
). Updates of the project are
available at the website
www.eliminatedengue.com
.
Jeffery et al. (2009)
report on efforts to characterize the
Ae
.
aegypti
population in a Vietnamese village
before the release of mosquitoes containing a novel
Wolbachia
strain following the releases in Australia.
Such a release will raise regulatory issues regarding movement of genetically modified insects across
international boundaries (
Lehane and Aksoy 2012
).
One concern is that if
Ae. aegypti
is no longer an effective vector, the second vector,
Aedes albopictus
,
could continue to transmit dengue. However,
Ae. albopictus
also has been infected with the
w
Mel strain
of
Wolbachia
, which causes cytoplasmic incompatibility and blocks dengue transmission. Thus, both of
the main vectors of dengue might be amenable to replacing pest populations with genetically modified
