Does wetland rehabilitation need mosquito control?

Webb_estuarinewetlands_SydneyOlympicPark_2014Mosquitoes can be more than a nuisance. They pose health risks but could also erode the good will of the community for wetland rehabilitation projects. Wetland rehabilitation needs mosquito control.

It’s a warm February evening. A small and anxious group of residents have gathered in a local community hall to discuss the implications of a local wetland rehabilitation project. Some are angry. One of the first questions comes from an elderly gentleman. Close to tears, he explains how his grandchildren no longer visit due to the plagues of mosquitoes that engulf his property day and night. “What are you guys going to do about it?” he pleads.

I learnt a valuable lesson that night. Trying to explain the best mosquito repellent to use doesn’t go down too well when an audience is facing some significant nuisance-biting impacts around their homes. It doesn’t matter how much DEET is in the repellent, it may well work but is it something you need to wear all day just to get the day to day jobs done around the house? Something more substantial is required and, with hindsight, should have been in place before the first waves of mosquitoes left the local wetlands.

Coastal wetlands are under threat

Sea level rise and climate change  is putting pressure on saltmarshes and urbanisation is eating away land that would otherwise accommodate a landward shift in estuarine habitats. There is nowhere for saltmarshes to spread to so they’re destined to be swallowed up by mangroves. While the mangroves are valuable themselves, they don’t provide the same critical habitats required by many of the internationally protected migratory shorebirds that rely on saltmarshes. Saltmarsh habitats could well disappear from much of the east coast in coming decades if sea levels rise as expected and mangroves continue their march landward.

webb_landinglightswetlandsEstuarine wetlands and mosquitoes

Saltmarshes are home to one of our most important pest and vector mosquito species. While it is important to remember that Aedes vigilax is an Australian native animal and just as much a part of our wetland ecosystems as fish and birds, there is little doubt that it can have substantial impacts with regard to nuisance-biting and the transmission of Ross River virus.

Historically, many of the saltmarshes along the east coast were drained or filled to enable increased cattle grazing (although much of it was under the guise of protection from flooding). Tidal flows were cut off with the construction of levee banks and installation of flood gates. Notwithstanding the impacts of grazing, without tidal exchange, the habitats became brackish water to freshwater dominated systems with a dramatic change in vegetation. Saltmarsh and sedgeland vegetation was steadily replaced by reeds and rushes. Invasive plants such as Phragmites quickly took over many of these wetlands.

webb_floodgates_march2011Bringing back the tides

To combat the degradation of wetlands and impending loss due to climate change, there has been some ambitious wetland rehabilitation projects planned. One of the largest in the southern hemisphere is the Hexham Swamp Rehabilitation Project. Much can be learned from the experience in this wetland just west of Newcastle, NSW, and applied to rehabilitation projects, not only in Australia but overseas as well.

Rehabilitation of Hexham Swamp involved the staged opening of existing floodgates to reinstall tidal flows to an otherwise freshwater system. Many aspects of this project were considered and it is unsurprising that one major issue was the possible impact of mosquitoes. Mosquito populations were something of legend in this area, enough so that there is a “big mosquito” outside the local bowling club affectionately known as “Ossie the Mossie” (coincidently, “Ossie” celebrated her 20th birthday in March 2014).

One of the important considerations when assessing mosquito risk was that there had been a dramatic transformation of the areas surrounding the wetlands in the last 20 years. What was once agricultural land was now residential. This is the same situation right along the east coast of Australia, the rapid urbanisation and swelling residential populations along the coast have put people in the firing line of Aedes vigilax.

The prospect of mosquito control was raised in the early stages of the rehabilitation planning but there was great reluctance from the local authorities to head down that path. The problem is that broad scale mosquito control and ecological rehabilitation are often seen at opposite ends of the wetland management spectrum. I’ve experienced this many times first hand, from scepticism regarding the non-target impacts of biological larvicides to “Apocalypse Now” jokes as helicopters go about routine spraying of local wetlands.

Webb_MosquitoCollectionsIs there such a thing as “environmentally friendly” mosquito control?

The hangover from the actual and perceived impacts of pesticide use more than 50 years ago is still present in the minds of many responsible for managing local wetlands. I say perceived as the development of environmentally sustainable mosquito control programs over the past two decades may not be appreciated amongst those charged with managing wetlands and wildlife.

I feel we need to continue building the case for the range of mosquito control strategies available for our coastal wetlands. Not only do we need to convince local authorities that mosquito populations can be minimised without adversely impacting the local environment but that mosquito control should be a critical consideration in wetland rehabilitation projects. It also has the potential to reduce mosquito-borne disease.

We know that the direct non-target impacts of Bacillus thuringiensis israelensis and s-methoprene are minimal and there is growing evidence that the indirect impacts on local wildlife due to reduced mosquito populations isn’t a major concern. Well-designed projects can also minimise the frequency of treatments while reducing peaks in mosquito activity.

It seems our coastal bats populations are mostly eating moths, not mosquitoes so there is unlikely to be any significant impact on these bats resulting from reduced food. There is no reason why the judicious use of larvicides can’t knock the top off abundant mosquito populations, reduce the pest impacts on local community and not pose a risk to local wildlife. Perhaps it should be considered a critical component of wetland rehabilitation?

redkneeddoteral_kooragangisland_march2015Mosquito control and wetland rehabilitation

In speaking with wetland managers, I try to instil with them the importance of mosquito control. There is a risk that swarms of nuisance biting mosquitoes may erode the good will in the community for wetland rehabilitation. These systems, particularly in the early phases of rehabilitation don’t represent pristine environments and while there may not be a desire to establish ongoing mosquito control programs, some control may prove useful while the wetland comes back into balance with the changed environmental conditions.

Rehabilitation takes time and while there is substantial breakdown of freshwater vegetation it is not going to be ideal for fish and other mosquito predators. It is likely to provide ideal conditions for mosquitoes. Over time, however, fish are likely to increase in both their abundance and penetration into the wetlands and greater tidal flushing will make many of the wetland habitats generally unsuitable for mosquitoes.

Perhaps there is benefit in undertaking control as a show of good will to the local community? After all, engagement with the local community will be critical in the success of wetland rehabilitation projects.

The restoration of tidal flows to Hexham Swamp resulted in an initial increase in the abundance of Aedes vigilax. These increases resulted in substantial nuisance-biting impacts. However, in subsequent seasons, the populations of Aedes vigilax levelled out to comparable levels to those of the surrounding estuarine wetlands. The net result has generally been that the long-term moderate increases in Aedes vigilax populations have been balanced by reductions in Culex annulirostris and Coquilettidia linealis populations as the wetlands shifted from freshwater to saline. The health of the wetlands, as well as the local estuary, is improving.

Mosquito control is only a short-term fix and if the rehabilitation of estuarine wetlands is not carefully planned, there may well be ongoing mosquito impacts. However, reducing any initial impacts will go a long way to ensuring continued engagement of the community with the local wetlands. Cost and the operational considerations may be a barrier for organisations unfamiliar with broadscale mosquito control but these issues can be overcome with the expertise that exists in many parts of the country.

In summary, it is important that mosquito management be considered in the planning process of major wetland rehabilitation projects. There is little doubt that such projects will be required into the future as saltmarsh habitats and other estuarine wetlands are threatened but protection wetlands shouldn’t mean increasing mosquito populations. A balance is required between conservation of environmental health and protection of human health.

A longer version of this article originally appeared in “Mosquito Bites” (the Bulletin of the Mosquito Control Association of Australia).

World Wetlands Day: Rehabilitation, Agriculture and Mosquitoes

hexham_floodgatesWetlands are some of the most important, but most threatened ecosystems in the world. February 2 is World Wetlands Day and an opportunity to celebrate local wetlands and raise awareness of their importance. Can we rehabilitate wetlands without creating more opportunities for mosquitoes?

What is World Wetlands Day?

World Wetlands Day is celebrated each year on 2 February and marks the anniversary of the signing of the Convention on Wetlands of International Importance in Ramsar, Iran, on 2 February 1971.

As described by the Australian Department of the Environment:

“World Wetlands Day was first celebrated in 1997. Since then government agencies, non-government organisations and community groups have celebrated World Wetlands Day by undertaking actions to raise public awareness of wetland values and benefits and promote the conservation and wise use of wetlands.”

The 2014 theme for World Wetlands Day is “Wetlands and Agriculture” and may, at first, seem a little unusual. However, wetlands play a critical role in supporting many agricultural pursuits by improving water quality and assisting water conservation, providing a buffer against flood and storm events, assisting nutrient removal from runoff and supporting populations of predators of agricultural pests.

rushesWetlands, agriculture and Australia

Wetlands, although important in many ways to local communities and economies, have not always had a healthy relationship with agriculture in Australia. Draining, filling and polluting of wetlands have all resulted from agricultural development in both coastal and inland regions of Australia. Debate regarding the allocation of inland river flows to environmental and agricultural uses continues today. However, there is an increasing awareness of the need to balance the interests of agriculture and wetland conservation in many regions and an integrated approach is required. Fortunately, many land owners are now actively engaged in sustainable land management practices and efforts are made to limit impacts to onsite and offsite wetlands.

Looking ahead, there are new opportunities too. There is much potential in carbon farming or “blue carbon” that may see an increase in wetland areas. At the least, this may provide a valuable opportunity to assign an economic value to our wetlands, something that is often difficult to achieve but may eventually help with their conservation.

Historically, coastal floodplains have been significantly impacted by flood mitigation, agriculture and urban development. Most importantly, the restriction of tidal flows through the construction of sea walls, levees, roads, railways and floodgates have substantially altered the hydrology of these environments leading to changes in flora and fauna. In many instances, the “reclaimed” land has been used for agriculture, particularly grazing livestock. The decision to install floodgates may have been driven by concerns regarding potential flooding and to increase available area for grazing, limited consideration appears to have been given to the potential impact on the environment. Over 4000 structures have been identified in NSW alone that influence tidal flows into coastal wetlands.

cowsRehabilitating wetlands impacted by floodgates and restricted tidal flows

Coastal wetlands in Australia are under threat on many fronts so where there are opportunities to rehabilitate degraded habitats, strategies should be implemented to improve environmental health. So, don’t you just open or remove the floodgates?

With tidal flows restricted from these degraded habitats for decades, there have been substantial changes in these local environments. Understanding how re-establishing tidal flows may impact the existing flora and fauna across the local estuary is critical.

One of the largest estuarine wetland rehabilitation projects in the southern hemisphere is the Hexham Swamp Rehabilitation Project near Newcastle, NSW. The wetlands cover approximately 2,000 hectares and rehabilitation plans have been underway for over 30 years. Floodgates were installed in 1971 and have resulted in significant changes to the local vegetation. While remnant areas of saltmarsh and mangrove remained, the exclusion of tidal water, as well as the accumulation of rainfall runoff, shifted the vegetation to a freshwater dominated system. In particular, the wetlands became dominated by extensive stands of Phragmites australis. While these dense stands of vegetation provided habitat for a range of birds, frogs and snakes, with regard to locally important wading birds, the quality of the habitat wasn’t up to scratch. With the loss of coastal saltmarsh a major concern for local authorities, a strategy was developed to reestablish tidal flows to Hexham Swamp.

hexham_grasslandExtensive hydrological model was undertaken to inform the strategy of floodgate openings. However, despite some complex modeling to predict how tidal waters would move into and out of the system, it really wasn’t until the floodgates were opened that the wetland hydrology could be measured. A staged opening of floodgates over a number of years was undertaken with all gates open in August 2013.

There has already been a dramatic change in the local environment. In areas where tides are now penetrating and increasing salinity, there has been a substantial die off in freshwater vegetation. This is now steadily being replaced with estuarine plants such as saltmarsh. There has been a big shift in the birds visiting the site too with an increase in waders in many areas. There are more fish and an increase in prawn populations in the local estuary has been credited to the openings of the flood gates.

redmudflatWhat about the mosquitoes?

It will come as no surprise that concerns regarding potential increases in mosquito populations were expressed at early stages of this rehabilitation plan. There were some key site-specific issues to consider here. Firstly, the Hunter estuary contains extensive existing and productive mosquito habitats. Hexham Swamp, while significant, is surrounded by a number of other extensive saltmarsh and mangrove environments that are well documented as productive habitats for the saltmarsh mosquito, Aedes vigilax.

The impacts of these saltmarsh mosquitoes as important vectors of Ross River virus, prompted the formation of the “Living with Mosquitoes” group. This group contains five adjacent local governments, as well as a number of other stakeholders, with oversight from the local health district. The group assists local authorities develop coordinated surveillance and community education programs to raise awareness of mosquito risk. Even without changes in the mosquito populations produced from Hexham Swamp, the region would still have an ongoing mosquito issue to address.

Tracking the mosquito populations and changes in their diversity and abundance with the reintroduction of tidal flows, a couple of key observations were made. Firstly, there was a dramatic decline in the abundance of “freshwater” mosquito populations. This was expected and it was hoping that any declines in freshwater mosquitoes would offset any increases in estuarine mosquitoes. Secondly, although an initial “first flush” of mosquitoes were produced following the introduction of tides, populations appear to have stabilsed (perhaps even fallen) in line with other habitats in the local estuary.

The factors contributing to the “first flush” are not completely understood but the most likely scenario is that an accumulation of mosquito eggs over previous years were laying in wait for those first big tides to flood in. Although some of these eggs would have hatched following major rainfall events, there would rarely have been the volume of water in the wetland following rainfall compared to the major tidal flooding events now the gates are open.

mangrovesOur experiences with the Hexham Swamp rehabilitation program show that it is possible to “bring back” estuarine wetlands that may have almost disappeared through the restriction of tidal flows and damaged caused by agriculture (particularly cattle grazing). It is also possible to improve the health of these wetlands without creating additional or increased mosquito problems. Surveillance and planning (and perhaps a little mosquito control) will be required but it appears that if the health of the wetland improves, mosquitoes can be maintained at reasonable levels. It is important to remember that mosquitoes are a natural part of Australia’s wetlands and eradication should never be an objective of management.

Have fun during World Wetlands Day 2014! Don’t forget to check out the free eBook on managing urban wetlands produced by the Sydney Olympic Park Authority.

Entomology 2013: Science Impacting a Connected World

IMG_7511The annual meeting of the Entomological Society of America takes place this week in Austin, Texas. I’ll be presenting a “virtual poster” on the mosquito-borne disease risk factors associated with wetland rehabilitation, urban development and climate change.

I wish I could be there in Austin. I was luck enough to visit in February 2012 when I attended the annual meeting of the American Mosquito Control Association. It is a wonderful city and I hope to make it back someday soon.

IMG_5671Even though it will only be “virtual” attendance, I’m still excited about sharing my work at this meeting. It summarizes some of the my major research interests that revolve around the use of urban planning to assist the reduction in mosquito-borne disease. Particularly with regard to wetland rehabilitation and wildlife management. The use of planning instruments is important and just as authorities reconsider the approach to urban plannign in bushfire prone areas, perhaps authorities should consider approving new developments in areas where another hazard of the Australian environment is present…..mosquitoes. Some councils are already aware of the risks and attempting to manage those risks.

The Saltmarsh Mosquito (Aedes vigilax) (Photo: Stephen Doggett)

The Saltmarsh Mosquito (Aedes vigilax) (Photo: Stephen Doggett)

Although the option to discuss my poster with attendees via Skype isn’t available this time, I hope that there is a bit of interest via Twitter. Check out #EntSoc13

Here are the details of my poster:

Managing mosquito-borne disease risk in response to weather, wetlands and wildlife in coastal Australia

Cameron E Webb

Mosquito-borne disease management in Australia faces challenges on many fronts. Many gaps exist in our understanding of the drivers of mosquito-borne disease risk, particularly with regard to Ross River virus (RRV) that causes a potentially severe flu-like illness. Notwithstanding the environmental drivers of mosquito abundance, the role of interactions between mosquitoes and wildlife may play a role in disease outbreaks. Local authorities in coastal Australia responsible for the management of new residential developments and wetland rehabilitation projects are increasingly aware of strategies to reduce mosquito-borne disease risk. Mapping actual and potential mosquito habitats, with consideration to the environmental drivers of mosquito abundance, such as rainfall and tidal inundation of estuarine wetlands, can inform an assessment of nuisance-biting and public health risks. These assessments can further inform urban planning approvals and adaptive management of wetlands. “Mosquito risk zones” based on mosquito-specific dispersal ranges from local habitats, characterised by vegetation type and potential environmental drivers of mosquito abundance, are being used to guide the design of new residential developments. In conjunction with these developments, constructed wetlands and other water conservation approaches (e.g. rainwater tanks, stormwater infrastructure) are assessed with regard to the potential to produce pest mosquito populations. Site-strategies to reduce these risks are considered. The role of macropods in urban mosquito-borne disease outbreaks, particularly RRV, requires further investigation. The presence of macropods has been shown to increase the risk of mosquito-borne disease. Studies have shown that RRV is more likely to be isolated from local mosquitoes in regions where macropods are present. Therefore, the management of wildlife corridors between urban developments and wetlands may increase the public health risks. Environmentally sensitive mosquito control strategies may be required to reduce the risks where suitable mosquito habitats and wildlife occur close to residential developments.

If you’re at ‘Entomology 2013’, check out my poster on Saturday, November 9, 2013: 3:20 PM (Austin time) in Meeting Room 11 AB (Austin Convention Center).

You can also view the poster here.

The London (down) underground mosquito

Culex_molestus_Photo_StephenDoggettOur latest publication in the Australian Journal of Entomology marks the end of a three year research project investigating the biology of a unique introduced mosquito species, Culex molestus, in Australia.

We generally think of nuisance-biting mosquito problems being confined to tropical regions, or at least warm summer conditions. Well, imagine you’re in London in late September 1940. You’re taking shelter in the underground during The Blitz. It is crowded and cold. You’re bitten by mosquitoes too. You’re being bitten by Culex molestus. It is often commonly referred to as the London Underground mosquito and has already been the subject of some fascinating research that has shown how the mosquito has adapted to life within the London underground.

Culex molestus was first described from Egypt in 1775. The mosquito is unique in that it is closely associated with subterranean habitats across the temperate regions of the world, from underground train networks to flooded basements to septic tanks. The species has adapted to these habitats by gaining the ability to mate without the need to swarm (a phenomenon known as stenogamy) and by dropping the requirement of a blood meal to develop the first batch of eggs (a phenomenon known as autogeny). You can read about our previously published work on this here.

Londoners take refuge in the Underground during the Blitz. Taken from “The Tube 150 Anniversary: London Underground, Its Life In Pictures ” Huffington Post UK

The Culex pipiens subgroup of mosquitoes includes a number of globally important vectors of disease-causing pathogens but there are distinct genetic and biological differences between these species that influence their role in transmission cycles. There are four member of the Cx. pipiens subgroup in Australia, Culex australicus, Culex globocoxitus, Culex quinquefasciatus and Culex molestus.

The last of these species, Cx. molestus, had not been the focus of substantial research for over 50 years until a research project by the Department of Medical Entomology and University of Sydney commenced in 2010. The project was designed to address the gaps in our knowledge of these species with a view to assisting in the assessment and management of disease risk associated with this species.

This work was primarily undertaken by Nur Faeza Abu Kassim as part of her PhD candidature with generous support from Ministry of Higher Education Malaysia and Universiti Sains Malaysia.

How did the mosquito get to Australia?

The most cited theory to explain the introduction of Cx. molestus into Australia is that it was through military movements into Melbourne during World War II. This was based on an absence of this species in Victoria during the pre-WWII period. Our research supported this theory.

There were no reports of this species in Australia prior to the 1940s. A review of distribution records for this species confirmed the presence of the species at over 230 locations confirmed that the mosquito has spread throughout the southern parts of Australia and in coastal regions as far north as Tweed Heads (NSW) and Geraldton (WA). No specimens have been reported from Queensland or Northern Territory.

Molecular analysis of specimens collected from throughout Australia, with reference to specimens from Asia, North America and Europe, indicated that Australian Cx. molestus shared the strongest genetic similarity with specimens from Asia. Perhaps the mosquito hitched a ride from Japan into the Pacific and then, with US military, in Australia?

IMG_0170

An example of subterranean habitats closely associated with the presence of Culex molestus

Buzzing (and biting) about all year long?

One of the interesting findings of our research was that the mosquito was active throughout the winter months around Sydney. Analysis of weekly trapping over a 13 month period indicated that the species does not display diapause. As well as generally being a cool-temperate climate mosquito species, perhaps the subterranean habitats provided a little “insulation” from the cold, keeping water temperatures just a little warmer than above ground pools and ponds?

Most of the other nuisance-biting pests disappear during the cooler months. There will occasionally be a few about, particularly during warmer winter days. However, for most local pest mosquitoes, it seems to be the minimum daily temperatures that drive mosquito activity more than maximum daily temperatures. In the case of Cx. molestus, they soldier on regardless.

What about the public health risks?

One of the last unanswered questions regarding the potential public health impacts of Cx. molestus is in relation to the ability of this mosquito to spread local and/or exotic viruses. While local viruses (e.g. Ross River virus) have been isolated from field collected specimens, there is yet to be a thorough investigation of the ability of this species to transmit endemic pathogens such as Murray Valley encephalitis virus or Kunjin virus.

I was involved in a research project assessing the risks posed in eastern Australia due to potential introduction of West Nile virus. Laboratory investigations and field collections provided some valuable information but, due to prevailing environmental conditions at the time, there were very few Cx. molestus collected during the study. We need to complete some of this work to gain a better understanding on how important a role Cx. molestus may play in local disease risk.

One of the key implications of our research is that it highlights the need for urban planners and engineers to consider the risks posed by above and below ground water storage for creating mosquito habitats. While much of my work previously has concentrated on the creation of wetlands and rehabilitation of other habitats in association with urban development, rainwater and storm water storage structures should be adequately designed to reduce mosquito risk.

The full reference for our most recent paper is below:

Kassim NFA, Webb CE and Russell RC (2013) Australian distribution, genetic status and seasonal abundance of the exotic mosquito Culex molestus Forskal (Diptera: Culicidae). Australian Journal of Entomology 52: 185-198 [online]

ABSTRACT. Culex molestus was probably introduced into Australia in the 1940s and represents a potentially important nuisance-biting pest and vector of disease-causing pathogens in urban areas. The aims of this study were to review the literature to determine the current and historical distribution of Cx. molestus in Australia, analyse the genetic similarity of specimens collected from various locations in Australia with reference to specimens from North America, Asia and Europe, and document the seasonal abundance of this mosquito in the Sydney region. Results showed that Cx. molestus is common in southern Australia, but there was no evidence that this mosquito is found north of latitude 28.17°S. Molecular analysis indicated that specimens from various locations throughout Australia shared strong genetic similarity and that it was most likely introduced from Asia, possibly through multiple introductions over the past 70 years. Analysis of the seasonal abundance of Cx. molestus indicated that the species does not display diapause during the cooler months. Consideration should be given to the unique biology and ecology of this species when assessing the public health risk and the surveillance methods required in the management of Cx. molestus within urban areas of Australia.

You can read a media release from the University of Sydney here. Our research was picked up by the local and international media in the past week or so too. You can read about our work in the Daily Telegraph, Newcastle Herald and Sydney Morning Herald.

Previous publications as part of this research project include:

Kassim NFA, Webb C.E. and Russell RC (2012) The importance of males: larval diet and adult sugar-feeding influence reproduction in the mosquito Culex molestus. Journal of the American Mosquito Control Association 28: 312–316

Kassim NFA, Webb C.E. and Russell RC (2012) Is the expression of autogeny by Culex molestus Forskal (Diptera: Culicidae) influenced by larval nutrition or by adult mating, sugar feeding or blood feeding? Journal of Vector Ecology 37: 162–171

Kassim NFA, Webb C.E. and Russell RC (2012) Culex molestus Forskal (Diptera: Culicidae) in Australia: colonisation, stenogamy, autogeny, oviposition and larval development. Australian Journal of Entomology 51: 67-77

Australian Mammal Society Conference

IMG_5671On Tuesday 9 July I’m presenting some work at the Australian Mammal Society conference at the University of NSW. The title of my presentation is “The role of macropods in mosquito-borne disease: Implications for urban development and wetland rehabilitation” (my coauthors are Stephen Doggett (Medical Entomology, Westmead Hospital) and Mark Ferson (University of NSW/NSW Health).

Ross River virus causes around 5,000 cases of reported human disease every year but, as the symptoms can sometime be mild, the official data is probably an underestimate. The role of Australian wildlife in mosquito-borne transmission cycles is often overlooked. The emphasis is generally placed on mosquito populations and their relationship to environmental drivers of population abundance. We have some very good data on the types of mosquitoes responsible for transmitting RRV thanks to detection of the virus in wild caught mosquito populations and “vector competence” experiments in the laboratory.

There have only been a few studies looking at the role of wildlife. These studies have included serological surveys, isolation of pathogens from wildlife and laboratory studies investigating the titre and duration of viremia in infected animals. These studies have helped identify macropods as some of the key reservoir hosts of RRV in coastal Australia. However, we still don’t know much about how the local wildlife, mosquitoes and pathogens interact under the influence of local environmental and climatic conditions. In particular, how does the ecology of local macropods influence local mosquito-borne disease risk? To be even more specific, how may the conservation strategies of local wildlife at the urban fringe influence public health risks?

If you’d like to read more about RRV, there are two very good review papers here and here. For more on mosquito risk associated with urban development, see my piece here.

IMG_7562My presentation will concentrate on mosquito abundance and diversity, as well as the activity of mosquito-borne pathogens, from two estuarine river systems in Sydney. The Parramatta River and Georges River systems contain comparable mosquito habitat dominated by estuarine wetlands (i.e. saltmarsh and mangroves) but support very different populations of macropods. There aren’t any macropods along the Parramatta River. What we’ve found by studying these two systems can be used to assist in urban development plans where wildlife conservation may require increased awareness of mosquito population management.

Of course, I’m not suggesting that the conservation of macropods isn’t important. The point here is that local authorities must be aware that in regions where there are opportunities for interactions between mosquitoes and wildlife (particularly kangaroos and wallabies), public health risks will be higher. Increased mosquito populations in association with newly constructed or rehabilitated wetlands, particularly in urban areas, may risk only increase nuisance-biting impacts. However, at the fringes of our cities, the risks of disease caused by pathogens such as RRV must be considered. In these circumstances, mosquito management strategies should be more carefully considered.

The full abstract of my presentation is below:

Mosquito-borne disease risk in coastal regions of Australia is a concern for local authorities. Many gaps exist in our understanding of the drivers of mosquito-borne disease risk, particularly with regard to the role of interactions between mosquitoes and wildlife. Macropods have been identified as important reservoir hosts of mosquito-borne pathogens and the presence of kangaroos and/or wallabies is a critical factor in driving outbreaks of disease. What are the implications for urban development and wetland rehabilitation projects? To investigate the role of macropods in urban mosquito-borne disease outbreaks, mosquitoes and activity of Ross River virus (RRV) was investigated in two estuarine wetland systems in Sydney. The abundance and diversity of mosquitoes produced by the estuarine wetlands along the Parramatta River and Georges River are similar with the dominant mosquito Aedes vigilax. There are no macropods are present along the Parramatta River. Few isolations of RRV have been detected along the Parramatta River but significantly higher rates of RRV (as well as other mosquito-borne pathogens) have been detected from mosquitoes collected along the Georges River. In addition, public health investigation confirmed local acquisition of RRV disease in residents living along the Georges River. No locally acquired RRV disease has been confirmed from the Parramatta River region. The use of natural bushland wildlife corridors along the George’s River by macropods is increasing local disease risk in that region. The results have implications for urban planning where wetland creation and rehabilitation, as well as wildlife corridors, may increase local public health risks.

The full program for the Australian Mammal Society conference is available here.

UPDATE: There was a nice article by Nicky Phillips in the Sydney Morning Herald on 13 July covering this story too “Urban kangaroos, wallabies harbour Ross River virus

Summer mozzie media buzz

Trapping mosquitoes in the mangroves along the Parramatta River (from SMH 21 December 2012)

There is usually a bit of media interest in mosquitoes during the summer months.  As most people start thinking about lazy coastal holidays and endless BBQs, the topic of mosquitoes isn’t far from mind so it is no surprise that there is interest in the topic.

I was involved in two recent articles in local media. The Sydney Morning Herald ran a piece by Julie Power on my mosquito research and its contribution to understanding the health risks associated with coastal mosquito populations. This was a timely piece as NSW Health had recently issued a public health warning about mosquito numbers along the coast and the possible increased risk of Ross River and Barmah Forest virus during the holiday period.

The second article was by Matthew Kelly in the Newcastle Herald on my research project with Hunter-Central Rivers Catchment Management Authority on the Hexham Swamp Rehabilitation Project. After two years under relatively cool and wet La Nina weather patterns, mosquito populations associated with most coastal wetland areas were generally pretty low. The Newcastle Herald had run a story in early 2012 reporting our findings that mosquito populations associated with Hexham Swamp were actually relatively low. The shift back towards hot and dry El Nino conditions mark an increase in the suitability of habitats for the saltmarsh mosquito Aedes vigilax. We’re expecting to see increases in the abundance of this mosquito along the east coast of Australia over the coming summers. It will be interesting to see how populations of this mosquito associated with the Hexham Swamp Rehabilitation Project respond to these conditions.