Agriculture Reference
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Insect Technique' (IIT) through repeated
releases of male mosquitoes containing a
non-native strain of
Wolbachia
. Provided
only males are released, none of the matings
will result in viable offspring and the native
population is reduced without acquiring
the non-native
Wolbachia
strain. This
approach was successfully deployed in the
elimination of a small, isolated population
of the mosquito
Cx. pipiens quinquefasciatus
from a village near Rangoon (Laven, 1967).
Atyame
et al.
(2011) found that male
Cx.
pipiens quinquefasciatus
transinfected with
the
Wolbachia
wPip(Is) strain from
Cx.
pipiens pipiens
in Turkey showed complete
sterility in mating with
Cx. pipiens
quinquefasciatus
from La Réunion and they
displayed good mating competitiveness.
Similar work with
Aedes polynesiensis
, the
principal vector of lymphatic fi lariasis in
the South Pacifi c, showed that incompatible
males of this species were equally com-
petitive with wild-type males and high rates
of suppression occurred in cage experiments
(Brelsfoard
et al.
, 2008).
To overcome the risk of introducing
fertile females with the
Wolbachia
strain,
Brelsfoard
et al.
(2009) found that irradiation
of male pupae of
Ae. polynesiensis
at a
female sterilizing dosage of 40 Gy did not
lead to any loss of mating competitiveness.
Genetic sexing is another option to ensure
no females are released.
weakly than wMelPop (Eliminate Dengue,
2013b) and has less detrimental physio-
logical effects on this mosquito. Bian
et al.
(2013) reported the establishment of a stable
infection with
Wolbachia
strain wAlbB in
the important urban malaria vector
An.
stephensi
, which confers resistance to
P.
falciparum
malaria.
Open releases of adult
Ae. aegypti
males
and females with the wMel
Wolbachia
strain in early 2011 in two areas of 600-700
houses near Cairns, Queensland, Australia
led to virtual fi xation with the
Wolbachia
form (Hoffman
et al.
, 2011). A similar trial
with the more virulent wMelPop strain in
2012 led to positive results at fi rst, but
diminished over time (Eliminate Dengue,
2013b). This strain was also released in Tri
Nguyen Island in Vietnam in 2013 and after
11 weeks of releases 59% of mosquitoes on
the island carried
Wolbachia
(Eliminate
Dengue, 2013c).
Ae. aegypti
with a third
strain of
Wolbachia
that aims to demonstrate
strong dengue blocking capacity, similar to
wMelPop, was released into three areas of
Cairns in early 2013 (Eliminate Dengue,
2013a). Releases resulted in over 80% of the
Wolbachia
form by early June.
Use of genetic systems
Additional genetic approaches involve the
replacement of the native population of
mosquitoes by ones that have been altered
genetically. These approaches are at the
laboratory research stage. Examples are
RNAi and HEGs, described by McGraw and
O'Neill (2013).
Population replacement
If both male and female mosquitoes with a
non-native strain of
Wolbachia
are released
in suffi cient numbers, the
Wolbachia
will
tend to propagate through the population
due to its maternal inheritance and the CI
effect. If this
Wolbachia
strain reduces the
ability of the mosquito to transmit disease,
its introduction should result in a decline in
disease transmission.
The wMelPop
Wolbachia
strain derived
from
Drosophila melanogaster
can be stably
transinfected into
Ae. aegypti
, reducing
adult lifespan and blocking transmission of
dengue and chikungunya (Moreira
et al.
,
2009). Another strain from
D. melanogaster
,
wMel, blocks virus transmission more
RNAi
RNAi is a natural insect immune response
system that recognizes and combats invad-
ing viral RNA. This has been exploited to
enhance mosquitoes' ability to reject dengue
by inserting an inverted repeat gene from a
dengue virus 2 (DENV-2) genomic RNA into
the insect's DNA. This triggers the RNAi
response and protects the mosquito from
colonization of its tissues by the dengue
virus when encountered through blood
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