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Managing mosquitoes in coastal wetlands

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The mosquitoes associated with estuarine wetlands represent some of the most important pest species in Australia. The saltmarsh mosquito, Aedes vigilax, and the southern saltmarsh mosquito, Aedes camptorhynchus , are both adapted to estuarine conditions and are often exceptionally abundant during periods of favourable environmental conditions. In those regions where abundant populations occur, these species play a locally significant role in the transmission of disease-causing pathogens, in particular Ross River virus and Barmah Forest virus. A range of strategies are available to manage the risks associated with these estuarine mosquitoes. These may include the use of control agents targeting the aquatic immature mosquitoes and/ or habitat modifications that reduce the suitability of estuarine habitats. Local authorities must remain mindful of these strategies as an increased abundance of mosquitoes in association with wetland construction and rehabilitation projects may be a concern. While the ecological importance of these estuarine mosquitoes has not been fully demonstrated, any mosquito management program must consider the indirect impacts of mosquito population suppression, particularly on insectivorous vertebrates that may utilise mosquitoes as a food supply. Mosquitoes are a natural part of estuarine wetlands and living with the risks associated with mosquito-borne disease requires balance between reducing the nuisance-biting and public health risks while minimising any adverse environmental or ecological impact of mosquito management activities.
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Chapter 3.6 — Managing mosquitoes in coastal wetlands 321
3.6 Managing mosquitoes in coastal wetlands
Dr Cameron Webb1,2
1University of Sydney & Pathology West - ICPMR Westmead, Westmead,
Australia
2Marie Bashir Institute for Infectious Diseases and Biosecurity, University of
Sydney, Level 3 ICPMR, Westmead Hospital NSW 2145
Australia
Abstract
The mosquitoes associated with estuarine wetlands represent some of the
most important pest species in Australia. The saltmarsh mosquito, Aedes
vigilax, and the southern saltmarsh mosquito, Aedes camptorhynchus, are
both adapted to estuarine conditions and are often exceptionally abundant
during periods of favourable environmental conditions. In those regions
where abundant populations occur, these species play a locally signicant
role in the transmission of disease-causing pathogens, in particular Ross River
virus and Barmah Forest virus. A range of strategies are available to manage
the risks associated with these estuarine mosquitoes. These may include
the use of control agents targeting the aquatic immature mosquitoes and/
or habitat modications that reduce the suitability of estuarine habitats.
Local authorities must remain mindful of these strategies as an increased
abundance of mosquitoes in association with wetland construction and
rehabilitation projects may be a concern. While the ecological importance of
these estuarine mosquitoes has not been fully demonstrated, any mosquito
management program must consider the indirect impacts of mosquito
population suppression, particularly on insectivorous vertebrates that
may utilise mosquitoes as a food supply. Mosquitoes are a natural part of
estuarine wetlands and living with the risks associated with mosquito-borne
disease requires balance between reducing the nuisance-biting and public
health risks while minimising any adverse environmental or ecological impact
of mosquito management activities.
Introduction
Mosquitoes are a natural component of coastal
estuarine wetlands. Given the threats to coastal
wetlands posed by urbanisation and climate
change, considerable effort is being placed on
the conservation and rehabilitation of these
environments. Unfortunately, mosquito-borne
disease is a concern for authorities in coastal
Australia. The most important mosquito species
involved in transmission of mosquito-borne
pathogens in coastal regions are mosquitoes
associated with estuarine wetlands (Russell 1998)
and there is a potential threat that these risks may
increase in the future under the inuence of a
changing climate (Russell 2009). Notwithstanding
the public health risks associated with these
mosquitoes, nuisance-biting impacts from biting
insects associated with estuarine wetlands can be
substantial and may have wide ranging impacts on
local communities (Ratnayake et al. 2006).
Local authorities charged with the task of
managing coastal estuarine wetlands must be
mindful of the risks associated with mosquitoes.
These mosquitoes can often disperse widely from
wetlands, resulting in impacts far beyond the
boundaries of the wetlands themselves (Webb and
Russell 1999; Vally et al. 2012). However, despite
the potential pest and public health risks, it must
be remembered that these estuarine mosquitoes
are Australian native animals and are a natural part
of estuarine ecosystems. These mosquitoes may
even serve an important ecological role in some
regions as a potential food sources for insectivorous
birds, mammals and arthropods. In particular,
recent studies have indicated that mosquitoes,
along with moths, provide food for some species
of insectivorous bats in coastal environments
(Gonsalves et al. 2013).
While there is a range of strategies are available to
reduce mosquito risk (Mosquito Control Association
of Australia 2008; Becker et al. 2010), not all
strategies will be considered appropriate under all
circumstances. The use of insecticides, biological
control and habitat modication may all reduce the
production of adult mosquitoes from the wetlands,
insecticides may also be used to reduce the impacts
of these adult mosquito populations beyond the
wetlands themselves. While the most commonly
used mosquito control agents currently have
been shown not to have direct adverse impacts
on non-target organisms (Russell and Kay 2008),
and broadscale mosquito control has been shown
to reduce the risks of mosquito-borne disease
(Tomerini et al. 2011), a balance between the
benets to human health, amenity of the
local community and environmental health is
required when mosquito management strategies
are implemented.
What health risks may be posed by
local mosquitoes?
Ross River virus (RRV) and Barmah Forest virus
(BFV) are the two mosquito-borne pathogens that
cause the most human illness in Australia. While
the symptoms can vary greatly between individuals
and include fever and rash, infection with either
of these viruses may result in a condition known
as polyarthritis, with arthritic pain in the ankles,
ngers, knees and wrists. Generally, the rash tends
to be more pronouced with BFV infection but the
arthritic pain is greater and longer lasting with
RRV infection (Russell and Kay 2004). The disease
resulting from infection with these pathogens are
“notiable diseases” in Australia and, given the
potential variability in symptoms, human infection
is only recorded in the ofcial statistics following
conrmation of infection with a blood test. There
are, on average, approximately 5,000 notications
of human disease caused by these two viruses
combined per year across Australia (Russell and
Kay 2004). The diseases are not fatal but can be
seriously debilitating.
There is a common misbelief that mosquito-borne
disease risk is only a problem for northern Australia.
However, major outbreaks of illness resulting from
RRV and BFV infection have occurred in southern
states including the NSW south coast, Victoria,
Tasmania and southern Western Australia (Russell
1998; Russell and Kay 2004).
The drivers of mosquito-borne disease in coastal
Australia can be complex with transmission
cycles generally requiring the presence of suitable
reservoir hosts (mostly birds and/or mammals) as
well as abundant mosquito populations. While
some debate surrounds the reservoir hosts of BFV,
the locally signicant hosts of RRV are generally
considered to be macropods (i.e. kangaroos and
wallabies) (Russell 2002). As a consequence,
regardless of the abundance of mosquitoes, in the
absence of suitable reservoir host populations,
public health risks associated with mosquitoes will
remain low.
The risks of arbovirus transmission in metropolitan
areas is generally lower than in rural areas as
habitats capable of producing substantially large
mosquito populations are low, as is the abundance
Chapter 3.6 — Managing mosquitoes in coastal wetlands 322
of suitable reservoir hosts. Given that it is the
coastal areas where urban developments are
expanding closer to estuarine wetlands, contact
between mosquitoes, wildlife, pathogens and the
community is increasing the risks of mosquito-
borne disease. However, human to mosquito to
human (thus occurring without the involvement of
an animal) transmission of arboviruses is suspected
to have occurred in some circumstances within
urban environments (Ritchie et al. 1994).
Mosquito biology
Despite the diversity of mosquitoes in Australia,
and the range of habitats in which they’re found,
the basic life cycle is similar for most species. This
is the case for mosquitoes associated with
estuarine wetlands.
They are small blood sucking insects that belong to
the family of ies called Culicidae (Order Diptera).
They have a relatively short but complex life cycle
consisting of eggs, four aquatic larval stages
(instars), a pupal stage and an adult stage (Becker et
al. 2010).
Depending on the species, eggs are laid either
on the water surface (usually with eggs in the form
of a oating raft) or on a frequently inundated
substrate (usually singly or in small groups). In the
case of estuarine mosquitoes, eggs can remain
viable until favourable environmental conditions
occur. On hatching, the young larvae (commonly
called wrigglers) feed continuously on aquatic
particulate matter although the immature stages
of some mosquitoes are predatory and will
consume other mosquito larvae. The immature
mosquitoes grow through four different instars
or moults until the nal larval stage develops into
a pupa (commonly called tumbler) from which
the adult mosquito emerges approximately 2
days later. The length of larval development is
primarily dependent on water temperature and
the availability of food. During the warmer months,
it generally takes 7-10 days from the hatching of
larvae to the emergence of adults.
On average, a female mosquito may live for up to
3 weeks but the lifespan of the male mosquito
is much shorter. Both adult male and female
mosquitoes will feed on nectar and plant uids, but
only the female feeds on blood. The extra nutrients
provided by the blood meal is required specically
for egg development. Mosquitoes identify potential
blood meals by detecting carbon dioxide, body heat
and the “smell” produced from the chemical cocktail
of compounds found on the host’s skin. While some
mosquito species have specic host preferences
(e.g. birds, mammals, amphibians), many are
generalist feeders and will readily bite humans. It
is important to note that very rarely do mosquitoes
emerge from the wetlands as adults infected with
pathogens, mosquitoes will almost always need to
bite an infected animal before becoming infected,
and subsequently infective.
After feeding, the female will nd a resting place
to digest the blood meal and develop eggs before
ying off to deposit them in a suitable habitat.
This process may take many days. It is typically not
until the eggs have been laid and the mosquito
seeks out another blood meal that transmission
of pathogens can occur. For the mosquito to
transmit a pathogens, the salivary glands of the
individual must be infected. When the nds a host,
they will inject a small amount of saliva to assist
blood feeding and it is this route of pathogen
transmission that results in the infection of a new
host. If the salivary glands are not infected, the
mosquito cannot transmit the pathogen. There
are complex relationships between pathogens and
mosquitoes, not all species can transmit pathogens.
For example, for the 300 mosquito species in
Australia, only one species can transmit dengue
viruses (the distribution of this mosquito is limited
to Far North Queensland) but over 20 species can
transmit RRV (Russell and Kay 2004).
What mosquitoes are associated with
estuarine wetlands?
Estuarine wetlands are harsh environments but
some mosquito species have adapted to these
often highly saline and ephemeral habitats. The
saltmarsh mosquito (Aedes vigilax), southern
saltmarsh mosquito (Aedes camptorhynchus),
Hexham grey mosquito (Aedes alternans) and
banded saltmarsh mosquito (Culex sitiens) are the
most common species found in tidally inuenced
estuarine wetlands. A much wider range of species
can be found in the brackish water habitats that
adjoin many estuarine wetlands but, even though
some of these species may represent locally
important pest species, their importance of often
over shadowed by the substantially more abundant
estuarine mosquitoes (Table 3.6.1).
Aedes vigilax
Aedes vigilax (Figure 3.6.1) is one of the most
important pest mosquitoes in Australia. As well as
being a severe nuisance-biting pest, it has also been
shown to play an important role in the transmission
of mosquito-borne pathogens (Russell 1998). It is
Chapter 3.6 — Managing mosquitoes in coastal wetlands 323
found in the majority of coastal regions of Australia,
with the exception of Tasmania, and molecular
studies have shown that there may be genetic
differences between populations between different
regions (Puslednik et al. 2012).
The mosquito is closely associated with tidally
inuenced habitats within estuarine wetlands
(Webb and Russell 1997) (Figure 3.6.2). The
mosquito is generally less common in upper
saltmarsh communities dominated by sedges
and rushes and, although the mosquito will lay
eggs within mangroves (specically at the base
of pneumatophores), it is more commonly found
in association with Sarcocornia quinqueora and
Sporobolus virginicus (Kay and Jorgensen 1986;
Gislason and Russell 1997) (Figure 3.6.3). It is,
however, important to note that that modications
to either saltmarsh or mangrove communities
through restricted tidal ows and drainage
can greatly increase the productivity of these
habitats (Figure 3.6.4). In some circumstances, the
production of abundant Aedes vigilax populations
can be a symptom of degraded wetlands. This is
particularly the case for mangrove communities
where restricted tidal ows resulting from habitat
modications (e.g. sea walls, levee banks, pathways,
rail lines etc) reduce the frequency of ushing
events and distribution of predators (e.g. sh) and
consequently increase the suitability of habitats for
mosquitoes (Webb and Russell 1999). Well ushed
mangrove habitats typically do not provide suitable
conditions for Aedes vigilax (Figure 3.6.5).
The key areas within the wetlands that produce
the most Aedes vigilax are determined by a range
of complex issues. It is not only the presence of
preferred plant species but also the local tidal
inundation regimes and availability of suitable
depressions and/or pools within the habitats. The
mosquito has the ability to develop its rst batch
of eggs without the need for blood (a phenomenon
known as autogeny) (Hugo et al. 2003), ensuring
that the next generation of mosquitoes is ensured
within suitable habitats. The eggs of Aedes
vigilax can remain viable in the environment for
long periods of time, possibly years. Hatching is
triggered by inundation of the wetlands by tides or
major rainfall events. During the warmer months,
the immature mosquitoes can complete their
Mosquito species Habitat associations Public health risks
Aedes alternans
Tidally inuenced saltmarsh but can
also be found in freshwater habitats.
Larvae are predatory and feed on other
mosquito larvae.
Potential nuisance-biting pest but is
not considered an important vector
of RRV or BFV.
Aedes camptorhynchus
Can be found in saline habitats but more
common in brackish-freshwater habitats
such as sedgelands to ooded grasslands
adjacent to estuarine wetlands.
Severe nuisance biting pest and
vector of RRV and BFV. One of the
most important pest species in
coastal Victoria, Tasmania, SA and
southern WA.
Aedes vigilax
Tidally inuenced saltmarsh but also
other saline and brackish water habitats
such as ooded sedgelands and coastal
swamp forests. Travels many kilometres
from larval habitats.
Severe nuisance biting pest and
vector of RRV and BFV. One of the
most important pest species in
coastal regions of NSW, QLD, NT
and WA.
Culex sitiens
Permanently inundated saline to brackish
habitats, including saltmarsh and
mangroves.
Bird feeding mosquito and not
considered a nuisance-biting pest.
Not considered an important vector
of disease.
Verrallina funerea
Saline and brackish habitats including
coastal swamp forests and the margins
of saltmarsh. Does not travel far from
larval habitats.
Severe nuisance-biting pest and a
vector of RRV and BFV.
Table 3.6.1. The habitat associations and public health risks associated with key mosquito species associated with estuarine wetlands
in Australian.
Chapter 3.6 — Managing mosquitoes in coastal wetlands 324
development in less than a week. Consequently,
population increased in Aedes vigilax can be
predicted based on the environmental drivers
of temperature, rainfall and tides from regions
across Australia (Webb and Russell 1999; Jacups et
al. 2008; Yang et al. 2008; Jacups et al. 2009; Hu et
al. 2010).
Many studies have investigated the spatial and
temporal egg-laying behaviour by Aedes vigilax
in estuarine wetlands. The highest densities of
egg shells are often concentrated in the zone
beneath vegetation rather than more open areas
and, on a larger scale, it is likely there would be
a concentration of eggs in an area of “preferred
inundation” (Dale et al. 1986; Ritchie 1994). This
zone of “preferred inundation” can be variable but
generally, it is found in the zone only inundated by
the highest tides of the month (i.e. spring tides).
More regular inundation of the wetland creates
relatively unsuitable conditions for Aedes vigilax
as eggs may not have sufcient period of drying
and suitable “maturation” to occur and nor suffer
damage by moving water, debris or predators.
While it may seem counter intuitive, the most
suitable environmental conditions for Aedes
vigilax occur during summers with below average
rainfall. These conditions, typically occurring
during El Nino weather patterns (i.e. hot and dry
summer along the east coast of Australia) when
the wetlands dry completely between tidal
inundation events. This drying process ensures
that habitats remain predator free, allow access
of mosquitoes to idea egg-laying sites and provide
an opportunity for deposited eggs to “mature”.
Conversely, during prevailing La Nina weather
patterns (i.e. relatively cool summers with above
average rainfall) the wetlands will generally remain
inundated for longer periods of time, allowing the
persistence of predator populations (i.e. sh) while
prohibiting access to preferred egg-laying sites by
the mosquitoes.
Nothwithstanding the potential for exceptionally
large populations of Aedes vigilax to occur during
periods of favourable environmental conditions, the
mosquito can disperse many kilometres from the
wetlands. There have been numerous qualitative
reports of Aedes vigilax adults being collected long
distances (e.g. over 20km) from the nearest saline
breeding grounds (Lee et al. 1984) and the results
of genetic analysis of Aedes vigilax populations
Figure 3.6.1. The saltmarsh mosquito, Aedes vigilax. (Photo:
Stephen Doggett, Medical Entomology, Pathology
West – ICPMR Westmead.)
Figure 3.6.2. An example of saltmarsh habitat on the north coast
of NSW that provides suitable conditions for Aedes
vigilax. (Photo: Cameron Webb, Medical Entomology,
Pathology West – ICPMR Westmead.)
Figure 3.6.3. An example of saltmarsh habitat in the Hunter
region of NSW that provides suitable conditions
for Aedes vigilax. The most suitable “hot spots”
for this mosquito in estuarine wetlands are these
pools surrounded by Sarcocornia quinqueora and
Sporobolus virginicus that are only lled by the
highest spring tides. (Photo: Cameron Webb, Medical
Entomology, Pathology West – ICPMR Westmead.)
Chapter 3.6 — Managing mosquitoes in coastal wetlands 325
suggest that the mosquito is dispersing widely
from local wetlands and resulting in little diversity
amongst local populations in SE QLD (Chapman et
al. 1999). Mark-release-recapture experiments have
found that marked mosquitoes were recaptured
between 1km and 5km from release points. The
active dispersal of mosquitoes from estuarine
wetlands can have a dramatic impact on nuisance-
biting and public health risks in the nearby
residential areas (Webb and Russell 1999;
Vally et al. 2012).
Aedes camptorhynchus
In southern states, Aedes camptorhynchus (Figure
3.6.6) generally replaces Aedes vigilax as the major
pest species, it is a serious biting pest and vector
of arboviruses including RRV and BFV (Russell
and Kay 2004; Barton and Kay 2009; Carver et
al. 2011). Although often found in the same
habitats as Aedes vigilax, Aedes camptorhynchus
is typically more commonly associated with less
saline conditions such as ooded brackish water
and freshwater marsh and pastures located
immediately behind saltmarsh and mangrove
wetlands (Webb and Russell 2001; Kokkinn et al.
2009). The habitats that appeared to be preferred
by this species are those more strongly inuenced
by rainfall beyond the regular direct inuence of
tidal inundation, although some tidal ooding may
occasionally occur (Barton et al. 2004; Kokkinn et
al. 2009). The species is not restricted to coastal
areas and has been recorded from freshwater
habitats extended distances from brackish habitats
(Dobrotworsky 1965).
Like many Aedes spp., the eggs of Aedes
camptorhynchus are desiccation resistant (Lee et
al. 1984; Bader and Williams 2011) and, as is the
case for Aedes vigilax, eggs are typically laid at
the base of vegetation. Laboratory studies have
demonstrated that these desiccation resistant
eggs will remain viable for up to 15 months
under ideal conditions (Bader and Williams 2011).
However, it is interesting that the eggs will not
always hatch when inundated, hatching appears
to be trigger by a range of factors that may reect
the evolution of adaptive strategies to harsh
estuarine environments where the occurrence of
suitable environment conditions (e.g. rainfall or
tidal inundation of wetlands) may be irregular. As a
Figure 3.6.4. An example of mangrove habitat at Sydney Olympic
Park that provides suitable conditions for estuarine
mosquitoes. (Photo: Cameron Webb, Medical
Entomology, Pathology West – ICPMR Westmead.)
Figure 3.6.6. The southern saltmarsh mosquito, Aedes
camptorhynchus. (Photo: Stephen Doggett, Medical
Entomology, Pathology West – ICPMR Westmead.)
Figure 3.6.5. An example of mangrove habitats at Sydney Olympic
Park. Mangrove habitats that are frequently ushed by
tides rarely provide suitable conditions for estuarine
mosquitoes. It is only when tidal ows and the
intrusion of predatory sh into the wetlands are
restricted that conditions become more suitable for
pest mosquitoes. (Photo: Cameron Webb, Medical
Entomology, Pathology West – ICPMR Westmead.)
Chapter 3.6 — Managing mosquitoes in coastal wetlands 326
result, highly variable seasonal abundance of
Aedes camptorhynchus is often observed (Barton
et al. 2004).
The seasonality of this mosquito differs from
Aedes vigilax in that it tends to be more abundant
in spring and autumn as opposed to summer
(Williams et al. 2009). In regions where these
two estuarine species are found, the peaks in
population abundance rarely overlap (Russell
2002). These differences in seasonal abundance
can be pronounced in areas such as southern NSW
where the species is far more abundant in the
cooler spring months as opposed to the warmer
summer months (Russell et al. 1992; Webb and
Russell 2001).
Aedes alternans
Aedes alternans is a large sandy coloured mosquito
species closely associated with estuarine wetlands.
Immature stages are often collected from estuarine
wetlands but they can also be found in fresh-
water habitats (Lee et al. 1984; Webb and Russell
2001). Although common in coastal regions, and
a known nuisance-biting pest, Aedes alternans is
generally considered a less important pest species
compared with other estuarine mosquitoes such
as Aedes vigilax and Aedes camptorhynchus as
the population abundance is relative low. The
population abundance of this species remains
low as the immature stages are predatory and
mostly rely on an abundance of immature stages
of Aedes vigilax to generate large populations (Lee
et al. 1984). Like all predator/prey relationships,
the abundance of prey larvae is a substantial
driver of predator populations but those predator
populations will always remain substantially lower
than the prey.
Although mosquito-borne viruses such as RRV
have been isolated from this mosquito (Ritchie et
al. 1997), laboratory studies suggest that Aedes
alternans is not an effective vector of RRV (Wells
et al. 1994) and is, consequently, not considered a
major public health concern.
Culex sitiens
The highly ephemeral nature of estuarine
wetlands generally favours Aedes species. However,
Culex sitiens is one mosquito that is commonly
found in permanently inundated saline to brackish
habitats (Lee et al. 1984; Webb and Russell 1997)
with studies indicating that survival of immature
stages is generally lower in highly saline habitats
(Mottram et al. 1994). This mosquito lays its
eggs as oating rafts on the water surface and,
unlike species such as Aedes camptorhynchus and
Aedes vigilax that can be abundant early in the
season due to a reserve of desiccation resistant
eggs in the wetlands, Culex sitiens must steadily
build up populations over the summer. As a result,
this mosquito is generally more common during the
late summer and autumn, and under favourable
environmental conditions, can generate abundant
populations (Webb and Russell 1999). However,
as this mosquito preferentially feeds on birds, it
is rarely considered a serious pest. While it isn’t
thought to play a role in the transmission of RRV to
humans (Fanning et al. 1992) but it is important to
note that arboviruses have been isolated from this
mosquito (Ritchie et al. 1997) and it may play a role
in spreading viruses between local bird populations.
Verrallina funerea
A mosquito species found at the margins of
estuarine wetlands is Verrallina funerea. This
species is considered a relatively important
nuisance-biting mosquito and is common in
northern NSW and Queensland where, in some
locations, it can be one of the most commonly
collected species in mosquito surveillance programs
(Ryan et al. 1999; Ryan and Kay 2000; Jeffery
et al. 2005). Studies have also shown that this
mosquito may play a role in local transmission of
RRV and BFV (Jeffrey et al. 2006). The species lays
desiccation resistant eggs in brackish to freshwater
ground pools within ooded coastal swamp
forests and she-oak woodlands (Figure 3.6.7) with
a stronger preference for those areas occasionally
ooded by tides (Ryan and Kay 2000). Although
Verrallina funerea is generally not considered to
disperse widely from larval habitats, pest impacts
are limited when compared with more widely
dispersing saltmarsh mosquitoes such as Aedes
vigilax and Aedes camptorhynchus. However, coastal
developments have brought people closer to their
habitats, increasing the relative impact of these
mosquitoes in recent years and there is qualitative
evidence that the mosquito can use corridors of
vegetation to move into residential areas adjacent
to their preferred habitats.
Other estuarine and brackish water mosquitoes
There are a number of mosquito species that may
be occasionally found in estuarine wetlands. Under
some circumstances, these species may cause
localised pest impacts but they are generally not
considered serious concerns for public health. A
range of Aedes, Anopheles, Coquillettidia, Mansonia
and Verrallina species associated with temporary
and semi-permanent freshwater and, occasionally,
brackish-water ground pools in coastal swamp
forests and coastal oodplain wetlands adjoining
Chapter 3.6 — Managing mosquitoes in coastal wetlands 327
estuarine wetlands. These habitats are usually
inundated by rainfall and would rarely, if ever, be
ooded by tides. During periods of above average
rainfall, when the saltmarsh may be inundated
by considerable rainfall runoff, some of the
mosquitoes associated with freshwater habitats
may be collected. The pest impacts posed by these
species will vary regionally as well as with seasonal
rainfall but will, generally, always be overshadowed
by the pest impacts of saltmarsh mosquitoes.
How do I know if mosquitoes are a
problem in my wetland?
A well designed monitoring program is essential
to assessing the mosquito risks associated with
estuarine wetlands. While mapping vegetation and
the extent of tidal inundation may provide a guide
to the potential suitability of the local wetland
to mosquitoes such as Aedes vigilax, there is no
substitute to sampling the local immature and
adult mosquito populations (Webb and Russell
2012). It is important to note that maintaining
a record of complaints and/or feedback to local
authorities on the level of nuisance-biting
activity will not provide a suitable measure of
mosquito populations. Information of this nature
is considered an unreliable basis for the design
of mosquito risk assessment and mosquito
management strategies.
Immature populations
While sampling adult mosquito populations will
provide a measure of loal mosquito abundance and
diversity, it is not possible to identify key mosquito
habitats without sampling immature mosquitoes.
There are strong habitat associations between
estuarine mosquitoes and habitats. However, those
habitats cannot be assessed based on the presence
of vegetation communities alone and, as well as
consideration being given to local tidal conditions,
the abundance of mosquitoes should be quantied
to guide mosquito risk management (Webb and
Russell 2012).
Immature mosquito populations can be sampled in
a variety of ways (Mosquito Control Association of
Australia 2008; Silver 2008) but most commonly are
sampled using a net or “dipper” (i.e. typically a 200-
300ml container). The actual size and design of this
Figure 3.6.7. An example of coastal swamp forest habitat on the north coast of NSW that provides suitable conditions for
estuarine and brackish water mosquitoes. (Photo: Cameron Webb, Medical Entomology, Pathology West –
ICPMR Westmead.)
Chapter 3.6 — Managing mosquitoes in coastal wetlands 328
sampling device is not critical. However, for
the purpose of on-going monitoring of local
mosquito populations, there should be consistency
in both the size and shape of the sampling
device as well as the way it is used to sample
mosquitoes. Studies have shown that individual
eld operators may bring subtle differences and
biases to their sampling methodologies. As a
consequence, it is important that appropriate
training is provided to eld staff to ensure
consistence in operational procedures.
A network of sampling sites that includes a number
of replicate samples across a range of habitats
types will form an important baseline measure with
which to base mosquito management decisions
(Webb and Russell 1999; Webb and Russell 2001).
The collection, and correct identication, of
mosquito larvae is the only reliable method of
identifying the breeding habitats and determine
the spatial and temporal distribution of productive
mosquito breeding sites. While there are taxonomic
keys (e.g. Russell (1993)) available for the
identication of immature mosquito stages,
these keys are generally based on 4th instar
larvae and to adequately record the diagnostic
features, specimens need to be mounted on slides.
It can often be easier for immature stages to be
returned to the laboratory and reared through until
development is complete and specimens can be
identied as adults.
Adult mosquito populations
Adult mosquito populations are generally sampled
using dry-ice baited light traps. The most commonly
used traps in Australia are known as Encephalitis
Virus Surveillance (EVS) traps (Rohe and Fall 1974)
(Figure 3.6.8). These traps consist of an insulated
“billy” can, a small motorised fan and collection
receptacle. Dry-ice blocks or pellets are used as
an attractant to draw in host seeking female
mosquitoes that are subsequently drawn through
the fan into the catch bucket or bag. Additional
chemicals, such as octenol, can be added to traps
to increase collections of Aedes spp. (Webb et
al. 2004) but are generally not required when
Figure 3.6.8. The foundation for effective mosquito management is a good surveillance program. The most commonly
used mosquito traps in Australia use carbon dioxide to attract mosquitoes. The abundance and diversity
of mosquitoes collected provides an assessment of mosquito risks and the effectiveness of mosquito
control programs. Specimens can also be tested to determine if they are infected with any mosquito-borne
pathogens. (Photo: Cameron Webb, Medical Entomology, Pathology West – ICPMR Westmead.)
Chapter 3.6 — Managing mosquitoes in coastal wetlands 329
general information on abundance and diversity is
required. Traps are typically hung in vegetation and
operated overnight. Traps set in exposed and wind
swept areas typically collect smaller numbers of
mosquitoes. Mosquito collections can be returned
to the laboratory and killed by placing into a freezer
for approximately 20 minutes. The dead specimens
can then be identied using taxonomic keys such
as Russell (1993). In addition, collections can be
tested to determine if mosquitoes are infected with
any pathogens (Doggett et al. 2009; van den Hurk
et al. 2012)
To measure the relative spatial and temporal
abundance of local mosquito populations, a
network of traps is usually operated around the
wetland to sample mosquitoes dispersing from
and into a wetland and local area (Webb and
Russell 1999). The exact number of traps will be
dependent on a range of factors including the
suitability of vegetation surrounding the wetland
and the diversity of wetland habitats themselves
that must be sampled. Additional traps may also
be operated at increasing distances from breeding
habitats to identify dispersal patterns of pest
species and identify areas of greatest pest impacts.
This additional trapping may provide important
information on the relative impact of estuarine
mosquitoes in nearby residential or recreational
areas compared to freshwater, brackish water or
“backyard” mosquitoes (Webb and Russell 1999;
Vally et al. 2012).
The timing and frequency of mosquito population
sampling is an important consideration since
mosquitoes have short life cycles and their
abundance closely linked to the environmental
factors. There are also differences in the seasonal
abundance of the three most common estuarine
mosquitoes, Aedes camptorhynchus, Aedes vigilax
and Culex sitiens. This is particularly the case
Aedes vigilax with population abundance closely
associated with tidal inundation of the wetlands
by tides or rainfall (Webb and Russell 1999).
Where weekly sampling of mosquito populations
is not possible, monitoring programs that require
a comparison of mosquito abundance between
wetlands must ensure that populations of Aedes
vigilax are sampled at similar periods in conjunction
with tidal and/or rainfall events. As mosquito larvae
can hatch from eggs and complete development
to adults within approximately 7 days during the
warmer months, sampling should be undertaken
approximately 10 days follow wetland inundation
to gain a measure of peak mosquito abundance.
There can be substantial differences in the
abundance of mosquitoes relatively to short-term
changes in tidal cycles (Gonsalves et al. 2013).
There are few quantitative measures of mosquito
abundance that determine that a wetland has a
“mosquito problem”. As mosquitoes are a natural
part of Australia’s estuarine wetlands, it should be
expected that there will be mosquitoes present and
active during the warmer months. The critical issue
is the relative impact of these populations and if
these populations are considered to be unusually
large from a local perspective. Building a data set on
local mosquito populations is critical and will allow
a comparison of changing mosquito abundance
with seasonal variability in environmental factors
(Webb and Russell 1999).
Mosquito population management
Reducing the nuisance-biting and public health
risks associated with mosquito populations
produced from estuarine wetlands should follow
the principles of Integrated Pest Management
(IPM). The basis for any integrated pest
management program is a multidisciplinary
strategy built on a site-specic mosquito-
monitoring program (Webb and Russell 2001;
de Little et al. 2012). There doesn’t need to be a
reliance on insecticide treatments of wetlands
but a consideration of all available strategies
(i.e. habitat modication, insecticides, biological
control, community education) within a regional
context that may offer the best approach (Webb
and Russell 2005; Webb and Russell 2007; Webb
and Russell 2012).
It would not be possible, or desirable, with
methods currently available to eradicate
mosquitoes entirely from coastal Australia. No
control strategy is 100% effective and there would
be nancial and operational limitations in many
regions to target all habitats. However, there are
options available for the use of control agents and
habitat modication that have been shown to
be effective and environmentally sustainable. All
strategies will have advantages and disadvantages
(Table 3.6.2) but through the prioritising of key
mosquito “hot spots”, it is possible to design a
mosquito management program and reduces
nuisance biting impacts (Webb and Russell 1999;
Webb and Russell 2001) and minimised public
health risks (Tomerini et al. 2011).
It is important to note that any mosquito control
activities should be undertaken with products
approved for use against mosquitoes and registered
with the Australian Pesticides and Veterinary
Chapter 3.6 — Managing mosquitoes in coastal wetlands 330
Medicines Authority (APVMA). The application of
mosquito control agents and/or the modication of
estuarine wetlands will require approvals from local
authorities (Webb et al. 2009) and the appropriate
legislation should be considered when developing a
local mosquito management program.
Controlling adult mosquito populations
Adult mosquito control is rarely undertaken in
Australia. For the most part, it is limited to periods
of epidemic virus activity or when exceptional levels
of nuisance-biting impacts are experienced (e.g.
post-ooding). The most commonly used products
Strategy Advantages Disadvantages
Environmental
modifcation
• Potential long term solution
without reliance on routine
application of control agents
• May have secondary benets
for rehabilitation of degraded
wetlands (e.g. restore tidal
ushing)
• Potentially cost effective
• May be legislative restrictions for application to
some estuarine wetlands
• Potentially expensive due to site-specic matters
• May not signicantly reduce overall
mosquito populations
• May impact some elements of wetland
ecosystem (e.g. increased soil moisture,
reduced crab populations, increase encroachment
of mangroves)
• May require regular maintenance to
maintain effectiveness
Bti
• Proven effective control agent
• Minimal non-target impacts
• Easy to assess treatment success
and reapplication possible if
treatment fails
• Reapplication required to control each generation
of mosquitoes
• Small window of application for
effective treatment
• Larvae quickly removed from ecosystem
• No residual control
• For environmentally sustainable programs,
aerial applications are the ideal strategy and may
be expensive
Methoprene
• Proven effective control agent
• Minimal non-target impacts
• Sustained release formulations
provide residual efcacy (i.e.
reapplication frequency reduced)
• Larvae are retained in ecosystem
for longer periods
• Potentially expensive
• Time consuming to apply sustained
release formulations
• Treatment assessment requires collection
of pupae
• No opportunity for reapplication if
treatment fails
Biological control
• Introduction of native sh
complementary to other wetlands
management objectives
• Very acceptable to community
• Not appropriate for highly saline and/or
ephemeral habitats
• Only sh species endemic to the local area
can be released
• Community may feel mislead if introductions do
not reduce mosquito impacts
Adulticides
• Ground based applications may
be effective in small areas (e.g.
isolated communities close
to wetlands)
• Harbourage/barrier treatments
potentially effective for home
owners close to wetlands
• Useful strategy in emergence
response to disease epidemics
• Difcult to achieve effective long term control
• Treatments may need to be repeated at
daily intervals
• Potentially signicant non-target impacts
• Expensive and requires operational capacity
of local authorities
• May not be acceptable to community
Table 3.6.2. Advantage and disadvantages of mosquito management strategies for estuarine wetlands.
Chapter 3.6 — Managing mosquitoes in coastal wetlands 331
are permethrin or synthetic pyrethroid based,
products. Known as adulticides, these products
are typically applied as either a “fog” or “mist”
delivering very small droplet sizes. Adulticides can
be expensive, their effectiveness is dependent on
favourable weather, multiple treatments are often
required and potential non-targets are a concern
as these products are not specic to mosquitoes.
Where estuarine mosquitoes are a problem,
adulticides may be a very ineffective way to control
mosquito populations as they disperse widely from
the wetlands. As a routine management option,
adulticides are not recommended.
In recent years, another insecticide application
strategy is increasingly used to reduce the
nuisance-biting impacts of biting midges and
mosquitoes associated with estuarine wetlands
is with “barrier treatments” or “harbourage
treatments”. This strategy most commonly involves
the application of the synthetic pyrethroid,
bifenthrin. The product provides a residual layer
of pesticide that kills resting mosquitoes and is
currently registered for treating mosquito resting
places (i.e. internal and external areas of domestic,
commercial, public and industrial buildings). While
some limited studies have shown that biting insect
populations immediately around treated areas can
be reduced (Hurst et al. 2012), there are, however,
some environmental concerns surrounding the
widespread use of this product, in particular for
non-target insects and aquatic organisms. There
are warnings on the label that the product is toxic
to bees, sh and aquatic organisms and that mud,
sand, mangroves and other aquatic habitats should
not be directly treated or exposed to spray drift.
Controlling immature mosquito populations
Given that the major mosquito pests associated
with estuarine wetlands can widely disperse
from local habitats, the most effective way to
reduce mosquito risk is to target immature stages
of mosquitoes. Historically, control agents used
in estuarine wetlands have had the potential to
cause non-target impacts and/or contribute to
the development of insecticide resistance in
local populations.
Prior to World War II, petroleum oils were commonly
used (Bertram 1927) although the extent to which
it was used in estuarine wetlands is not clear. These
oils were then replaced by organochlorides (e.g.
DDT) until the late 1960s when organophosphates
(e.g. temephos) become the most commonly used
larvicide. Concerns regarding the development of
resistance and the potential for non-target impacts
saw the reduced the use of temephos during the
early 1990s in favour of more environmentally
sensitive control agents (Russell and Kay 2008).
The most commonly used control agent in
estuarine wetlands is Bacillus thuringiensis
israelensis (Bti). This product is available in a
small number of commercial formulations and
is registered for use against mosquitoes by the
APVMA. The bacteria produce a protein crystal that
contains a number of microscopic pro-toxins which,
when ingested, are capable of destroying the gut
wall and killing mosquito larvae.
The greatest benet of Bti is that it is highly specic
to mosquito larvae, and very few non-target effects
have been recorded when the product is applied at
the recommended rates. The product does, however,
have some disadvantages in that there is little
residual activity, and efcacy is reduced in habitats
with a high organic content or when applied when
larval populations are young or nearing pupation.
This has operational implications for the use of
this product in estuarine wetlands. For the most
effective results, wetlands must be monitored
for inundation resulting from tides or rainfall and
treatment must be undertaken when immature
populations are most susceptible (Webb and
Russell 2001; de Little et al. 2011). As the temporal
abundance of estuarine mosquitoes can be highly
variable in response to environmental factors, it is
difcult to predict the need for treatment based
on tidal and rainfall data alone. A site-specic
monitoring program is essential.
The insect growth regulator, s-methoprene, is a
synthetic mimic of the juvenile hormone produced
by insect endocrine systems and is becoming
increasingly common for the control of estuarine
mosquito populations (Russell and Kay 2008).
When absorbed by the larvae, development is
interrupted and larvae fail to successfully develop
to adults, usually dying in the pupal stage. A
range of commercial formulations (including
liquid, slow-release solid pellets and briquets)
have been approved for use against estuarine
mosquitoes by APVMA. Although generally more
expensive than Bti, there are some advantages
to the use of this product due to the availability
of the sustained release formulations that may
provide longer periods of residual control in some
habitats. For areas that may be difcult to access
or where the production of mosquitoes may be
difcult to predict, treatment with s-methoprene
will be useful. One of the drawbacks to the use
of s-methoprene is that, as it does not kill the
immature stages, assessing the effectiveness of
Chapter 3.6 — Managing mosquitoes in coastal wetlands 332
treatments can be difcult and generally requires
the collection of pupae to be returned to the
laboratory to record emergence rates.
Habitat modication
Historically, dramatic modications were made
to coastal wetlands to reduce local mosquito
populations. Draining and lling saltmarshes, as
well as the construction of levee banks and sea
walls to reclaim land for agricultural and industrial
purposes, may have reduced mosquito populations
but these approaches had signicant adverse
impacts on the local environment. Such dramatic
approaches are not undertaken today but it is
interesting to note that as local authorities attempt
to rehabilitate some of these degraded wetlands,
the potential to increase local mosquito-borne
disease risk is a concern.
Advances in habitat modication techniques
have shown that the suppression of mosquito
populations is possible without reliance on the
use of insecticides or jeopardising the ora, fauna
or ecological function of the wetland itself. In
some cases, unusually large mosquito populations
may be identied as a symptom of degraded
wetlands and improving the health of the wetland
may reduce mosquito productivity (Webb and
Russell 1997; Webb and Russell 1999; Turner and
Streever 1999).
A range of modication strategies are available but
the key is to increase the frequency of tidal ushing,
improve the drainage of water, and maximise
access of sh to productive mosquito habitats.
These factors combine to create less favourable
conditions for estuarine mosquitoes. The most
common form of habitat modication currently
practiced on saltmarshes is the construction of
shallow, spoon-shaped channels that connect
pools and depressions on the saltmarsh, and
allow improved exchange of tidal water over the
marsh without severely impacting the hydrology
of the marsh. This strategy, known as runnelling,
has been shown to reduce mosquito productivity
in saltmarsh habitats dominated by Sarcocornia
quinqueora and Sporobolus virginicus (Dale 1993;
Dale and Knight 2012).
While studies have shown that runnels reduce
mosquito breeding in estuarine wetlands (Dale and
Knight 2012) without major adverse impacts to the
wetlands (Dale 2008), the promotion of increased
tidal inundation of the saltmarsh and the potential
for increased mangrove propagule dispersal and,
consequently, mangrove colonisation at higher
elevations on the marsh (Breitfuss et al. 2003). The
intrusion of mangroves into the saltmarsh may
represent a potentially signicant adverse impact
to the wetlands (Saintilan and Rogers 2013). Given
the scrutiny currently given to management of
coastal wetlands, it is unlikely that large scale
runnelling projects will be undertaken in the
future. However, in those areas where runnels
current exist, it is important to ensure that they
remain functional as, if they become block with
sediment and mangrove seedlings, the runnel may
be converted into a series of isolated pools and
enhance habitat conditions for mosquitoes.
Biological control
An effective biological control strategy through
the specic release of mosquito predators into
estuarine wetlands is unlikely to be effective. A
number of native sh (e.g. Pseudomugil signifer
(Pacic Blue-eye), Hypseleotris compressa (Empire
Gudgeon) and some Melanotaenia species
(Rainbowsh)) have been identied that may be
appropriate for mosquito control in Australia.
However, given the highly ephemeral nature of
habitats in which key pest species are found,
the specic introduction of sh is not a suitable
management strategy, particularly in the upper
saltmarsh (Morton et al. 1988). However, there are
still substantial gaps in our knowledge regarding
the role of sh in the control of immature mosquito
populations in mangrove habitats (Grifn and
Knight 2012). While native sh introductions alone
will not signicantly reduce mosquito populations,
they do provide an important component of
integrated mosquito management and may provide
a valuable link to the wider community promoting
environmentally sensitive mosquito management.
Chapter 3.6 — Managing mosquitoes in coastal wetlands 333
Case study: Mosquito
management at Sydney
Olympic Park
Estuarine wetlands close to urban centres
pose the greatest mosquito risk. As well as the
mosquitoes typically associated with these
habitats, given the likely modications that
have occurred to the wetlands, they may be
producing unusually large populations. One of
the largest areas of estuarine wetland in Sydney
is located at Sydney Olympic Park, NSW. The
wetlands are located within the Parramatta River
estuary approximately 20km from the CBD of
Sydney and are comprised of extensive areas
of saltmarsh and mangrove habitats. Many of
these areas had become badly degraded as a
result of restricted tidal ushing and ineffective
drainage of rainfall resulting from many decades
of modications (e.g. sea wall constructions and
other raised infrastructure).
Symptomatic of the degraded wetlands are
unusually large mosquito populations. The
issue of nuisance-biting mosquitoes was rst
documented in the 1920s with Aedes vigilax
identied as the most signicant pest species.
While the public health risks associated with
these mosquito populations are low, given
the absence of suitable reservoir hosts (i.e.
macropods), RRV has been isolated from
mosquitoes on occasion. More signicant,
however, are the nuisance-biting impacts
extended into nearby residential areas. Mosquito
populations were studied in the late 1980s and
identied the estuarine wetlands as the source
of unusually large Aedes vigilax populations.
During the mid-1990s, the impact of nuisance-
biting mosquitoes in the suburbs of Parramatta,
Ryde and Concord was so great that it became a
political issue and public meetings to discuss the
issue were commonly held during the summer.
Developing a mosquito
management program
Prior to 1998, there was a relatively ad hoc
approach to mosquito control with ground
based application of the organophosphate
insecticide temephos to some wetlands. This
was often on a weekly or bi-weekly basis during
summer but also in response to community
complaints. There was no integrated mosquito
monitoring program in place to inform or assess
treatment effectiveness.
In conjunction with the redevelopment of the
Sydney Olympic Park site and surrounding
suburbs, there was a need identied to develop
an integrated, ecologically sustainable strategy
to reduce mosquito risk. Two key approaches
were taken that included the rehabilitation of
the most degraded areas of estuarine wetlands
and a seasonal program of mosquito control
agent application. These two aspects of the
mosquito management strategy were supported
by a seasonal mosquito monitoring program of
adult and immature mosquito populations.
Mosquito monitoring
Investigations into the local mosquito fauna
identied over 30 species of mosquito associated
with a range of estuarine, brackish water and
freshwater habitats. As well as being associated
with the local wetlands, there were mosquitoes
associated with man-made structures also.
Research ndings indicated that population
increases of Aedes vigilax were triggered by
tides tides over 1.8m but that the magnitude
of those increases is dependent on the number
and actual height of tides over 1.8m. While
predictions of tidal heights provide a good guide
to the timing of potential increases, variation
between actual and predicted tide heights
can result in unexpected, or more extensive
than expected, inundation of the wetlands. In
addition, rainfall events in which 50 mm or more
rainfall recorded within three days is typically
sufcient to trigger a hatch of mosquitoes.
Populations are, consequently, likely to be
signicantly greater if there is a major rainfall
event or if rainfall and tidal ooding occur at the
same time.
Between the months of November and May
each year, adult mosquito populations are
sampled weekly at approximately 15 xed
trap sites across Sydney Olympic Park. The
abundance and diversity of mosquitoes is
recorded and compared to long-term averages
so that an assessment of relatively nuisance-
biting impacts can be assessed. The information
gathered also provides information on pest
mosquitoes associated with non-estuarine
habitats that may be responsible for any unusual
nuisance-biting impacts.
Chapter 3.6 — Managing mosquitoes in coastal wetlands 334
Larvicide treatments
The current treatment program was established
in 1998 and combines aerial (helicopter) and
ground based application of the biorational
control agent, Bti (Figure 1). The larvicide is
generally applied via helicopter but some areas
may require application from the ground.
The mosquito control program is based
on established operating procedures with
recommendations for control agent applications
based on the extent of wetland inundation and
abundance of newly hatched larvae at xed
monitoring sites across the estuarine wetlands.
Comparing the pre- and post-treatment larval
densities in each habitat as well as changes in
the relative abundance of adult mosquitoes
assesses the effectiveness of the treatment
program. On average, a reduction of between
80-95% of immature mosquitoes following
treatment is recorded. Since the program
commenced in 1998, there have been no reports
of any non-target impacts.
Habitat rehabilitation
One of the key mosquito habitats in the local
area was a stand of degraded mangroves. The
lack of effective ushing led to stunted growth
of mangroves, which in turn led to incomplete
canopy cover and establishment of saltmarsh
vegetation (the primary oviposition site for
saltmarsh mosquitoes) around those pools.
Few predatory sh could gain access to these
habitats. Sampling of these habitats routinely
found high densities of Aedes vigilax and Culex
sitiens during the summer months.
A tidal restoration project was designed,
while being informed by data on mosquito
populations, involving the construction of
primary and secondary channels throughout
the mangroves to improve tidal ushing (i.e.
increase the frequency of tidal ushing events
and increase the volume of water entering and
exiting the mangroves in each tidal ushing
event) (Figure 2). It was hoped that the increased
Figure 1. An example of coastal swamp forest habitat on the north coast of NSW that provides suitable conditions
for estuarine and brackish water mosquitoes. (Photo: Cameron Webb, Medical Entomology, Pathology
West – ICPMR Westmead.)
Chapter 3.6 — Managing mosquitoes in coastal wetlands 335
ushing would improve the health
of the wetlands as well as reduce
mosquito productivity.
Virtually all mosquito production within
the modied wetlands was removed. The
reduction in mosquitoes was so signicant that
the application of mosquito control agents was
no longer required. Many of the most productive
mosquito ‘hot spots’ were physically removed
as part of the channel construction process.
The key factors contributing to the decline
in mosquito production, as expected, were
increased tidal ushing and more widespread
sh movement. As mangrove health improved
and the canopy closed in, less suitable conditions
were present for mosquito oviposition sites
and there was a substantial reduction in the
number of pools that held water for sufcient
time to allow mosquito larvae to complete
development. Permeation of tidal and rainfall
into the substrate appears to be more effective
post-modication.
Figure 2. The rehabilitation of degraded mangroves at Sydney Olympic Park through the reintroduction of tidal ushing
signicantly reduced mosquito production to the extent that the application of insecticides was no longer
required. (Photo: Cameron Webb, Medical Entomology, Pathology West – ICPMR Westmead.)
Education & Awareness
A key component of the mosquito management
program at Sydney Olympic Park has been
proactive education and awareness of the local
community and stakeholders. Mosquitoes will
always be active during the warmer months
and, as the control program is not designed to
eradicate mosquitoes, appropriate measures
should be taken to avoid bites. It is particularly
important that appropriate information on
personal protection measures (e.g. topical
insects repellents) be provided to residents and
visitors spending time in the wetland areas (e.g.
mangrove boardwalks, bird watching hides). In
addition, residents, visitors and stakeholders
must be adequately informed of the timing of
mosquito control activities as to not alarm or
inconvenience those participating in activities
close to the wetlands. Strategies to ensure
the effective delivery of this information have
been a crucial part of the overall mosquito
management program.
Chapter 3.6 — Managing mosquitoes in coastal wetlands 336
Summary
Although mosquitoes are a natural part of the
estuarine wetland ecosystem, they have the
potential to be signicant nuisance-biting pests
and vectors of disease-causing pathogens.
Managing these pest and public health risks can be
a major concern for local authorities and may add
substantial nancial costs to wetland management.
While mosquito control may not always be required
or considered appropriate, an appreciation of
mosquito issues should be carefully considered by
wetland managers, and minimisation strategies for
mosquito populations. As well as having a duty of
care that local wetlands are not impacting the local
community, it may prove a substantial impediment
to gather support for wetland conservation and
rehabilitation projects is it is perceived that they
will increase mosquito populations.
References and further reading
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Barton, P. S., Aberton, J. G., and Kay, B. H. (2004).
Spatial and temporal denition of Ochlerotatus
camptorhynchus (Thomson) (Diptera: Culicidae)
in the Gippsland Lakes system of eastern Victoria.
Australian Journal of Entomology 43, 16–22.
Barton, P. S., and Weaver, H. J. (2009). Mosquito
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Becker, N., Petric, D., Zgomba, M., Boase, C., Madon,
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(2003). Mangrove distribution and mosquito
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... The TSI index, described by De Wet et al., converts temperature to a value between 0 and 10 (0 being temperatures at which the vector species cannot survive, and 10 being optimal temperatures) 5 . We utilized the threshold values provided by De Wet et al. for Culex annulirostris, a common vector for both BFV and RRV in Australia that inhabits a wide variety of environments, for the TSI analyses of BFV and RRV 30 . We determined threshold values for Aedes aegypti based on larval survival rates at various field sites in Australia for our dengue analysis; Ae. aegypti is the only dengue vector in Australia and thrives in urban areas 31 . ...
... Further, we made the assumption that most disease cases originate in areas of high human density (and hence the weather data was weighted by city population size). While the vector for dengue, Ae. aegypti, is highly adapted to urban environments and tends to thrive in man-made urban settings, the vectors for BFV and RRV are found in a much larger variety of habitats and may require a different method of weather abstraction 30,49 . One potential alternative to the sparse ground monitoring network would be to use remotely-sensed indicators as proxies to environmental conditions and vector habitats. ...
... This limitation might in part explain the high residual skew ( Figure S2 and Table S9), which indicates patterns in the disease time series beyond those accounted for in our models. Other environmental variables that could easily be incorporated into future versions of the models could include humidity or tidal data, both of which have been found to be significant indicators of vector-borne disease in Australia 30,50 . The high residual skew and kurtosis for the models also suggests that the models' predictive accuracy, especially for dengue, is limited. ...
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We conducted four trials in Sydney, New South Wales, Australia to compare the numbers of mosquitoes collected in Encephalitis Vector Surveillance (EVS) miniature light traps baited with carbon dioxide, carbon dioxide plus octenol or octenol alone. A total of 12127 mosquitoes belonging to 19 species was collected. For all species, more mosquitoes were collected in traps baited with carbon dioxide, with or without the addition of octenol, than with octenol alone. There were significantly more mosquitoes of most Ochlerotatus species collected in traps baited with carbon dioxide plus octenol than with carbon dioxide alone. The response of Anopheles spp. and Culex spp. was variable but, generally, there was no significant response to the addition of octenol to carbon dioxide baited traps.
Chapter
Hennig’s (1966) concept of hierarchies of monophyletic taxons based on common ancestors (with plesiomorphies or retained primitive, ancestral characters) and shared synapomorphies (homologous shared characters inferred to have been present in the nearest common ancestor but not in earlier ancestors nor in the taxa outside this group), has provided the theoretical basis for taxa formation. During the first decades following its proposal, it resulted in the establishment of cladistic trees where recency of common ancestry is the sole criterion for grouping of the taxa. The problem of ranking taxa and tree formation in a Darwinian evolutionary context was the next scientific step (Eldridge and Cracraft 1980). Opinions about what different nodes represent, how to deal with branch lengths, and how to rank monophyletic entities, have become part of a scientific field of its own (Britton et al. 2007). Applying both morphologic and genetic taxonomic methods, and working with different groups of characters to reveal evolutionary relationships between insect orders or families as monophyletic groups, is now becoming standard. In the new millennium this work has resulted in several new hypotheses of phylogenetic trees of Insecta. Wheeler et al. (2001) established the relationship between Diptera and Strepsiptera. Grimaldi and Engel (2005) in their comprehensive work on extinct and extant Insecta, summarized different hypotheses for Diptera. They accepted five suborders of Lower Diptera (Nematocera): Tipulomorpha, Psychodomorpha, Culicomorpha, Blephariceromorpha and Bibionomorpha. They placed Anisopodidae as a sistergroup to Brachycera (all higher Diptera) and discarded Nematocera as a paraphyletic group (including a most recent common ancestor and some, but not all, of it descendants). This view has been strongly advocated by Amorim et al. (2006). They recognised seven suborders/infraorders instead of Nematocera and added Brachycera as the eighth suborder/infraorder for the rest of the Diptera.
Book
Mosquitoes and Their Control presents a wealth of information on the bionomics, systematics, ecology, research techniques and control of both nuisance and disease vector mosquitoes in an easily readable style, providing practical guidelines and important information for professionals and laymen alike. Ninety-two European species and more than 100 globally important vector and nuisance species are included in the book. Most of them, including all European species, are described in the fully illustrated identification keys, followed by a detailed description of the morphology, biology, distribution and medical importance of each species, including over 700 detailed drawings. Mosquitoes and Their Control includes: Systematics and biology medical significance research techniques illustrated identification keys for larval and adult mosquito genera morphology, ecology, and distribution of the species identified in the keys biological, chemical, physical and genetic control of mosquitoes Mosquitoes and Their Control is a valuable tool for vector ecologists, entomologists, and all those involved with mosquito control, biology, ecology, and systematics world-wide. It will especially benefit those professionals, scientists and students dealing with mosquitoes and their control on a day-to-day basis. Society as a whole stands to gain from improved, environmentally responsible mosquito management programs designed on the basis of a broader understanding of mosquitoes and their control, as provided in this enlightening book. © Springer-Verlag Berlin Heidelberg 2003, 2010. All rights reserved.
Article
Aim Within Australia the Carpentaria Barrier has been identified as an important biogeographical barrier. Here we test this long-standing hypothesis using a medically important mosquito, Aedes (Ochlerotatus) vigilax. Location We obtained samples of Ae. vigilax from throughout its Australian distribution and from New Caledonia. Methods We constructed a distributional database from 602,417 specimens and obtained sequence data from 66 female specimens from 16 localities. The distributional database of Ae. vigilax comprised historical data from 13 organizations and was used to develop our molecular sampling strategy. Genetic structure within Ae. vigilax was examined via haplotype networks, FST values, analysis of molecular variance and neutrality test statistics based on one mitochondrial (cytochrome c oxidase subunit I, COI) and two nuclear (alpha amalyse and zinc finger) loci. The historical demography of Ae. vigilax was investigated using extended Bayesian skyline plot (EBSP) methods, with past migration rates estimated using migrate. Results We identified three distinct lineages within Ae. vigilax; however, two of the three lineages show a large distributional overlap across the Carpentaria Barrier. The mitochondrial locus suggested a pattern of significant genetic differentiation, with high FST values, significant genetic differentiation within the COI locus, and significantly more variation between the lineages than within. A higher number of migrants per generation were estimated for the overlapping lineages and both the neutrality test statistics and EBSP suggested the occurrence of post-population expansion in these lineages. Main conclusions Significant deviation from genetic neutrality, in combination with estimates of migration and the demographic history of Ae. vigilax lineages, suggests that the incongruence of the Ae. vigilax phylogeny with the hypothesized Carpentaria Barrier could be attributed to the separation of eastern and western populations of Ae. vigilax around 770 ka and subsequent secondary contact within the last 100 kyr. Sea-level and precipitation fluctuations within the Carpentaria area during the late Quaternary could have facilitated the current biogeographical patterns of Ae. vigilax. Mosquitoes represent one of the most medically important insect groups; however, understanding the factors that influence past and present distributions of mosquitoes is critical in the face of a range of emerging arboviruses.