How does a mosquito researcher mark the passing of seasons?

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Winter has come and gone for another year. For many people it means packing away the footy boots and starting to shop for swimwear. What about mosquito researchers? How does the passing of seasons change their work?

One of the things I love about my job (and occasionally loathe) is that it is primarily driven by the weather. On a weekly basis, i have to keep an eye on local rainfall, temperature fluctuations, and tidal cycles. All these things have a strong influence on local mosquito abundance and diversity. Add extreme weather events into the mix and things can become quite unpredictable! I can’t ignore the wind either, ever tried catching a mosquito in a howling gale?

Mosquitoes can be found right through the year in Sydney. Generally though, the year for me is divided into a series of milestones.

Goodbye winter, hello spring (plus migratory birds, daylight saving and end to rugby league)

There is a sound I’ve come to dread in recent years. The “awk-awk-awk…” of the channel-billed cuckoo. This migratory bird moves into Sydney from New Guinea and Indonesia around August and it’s call is a kind of siren that warns of the upcoming mosquito season. Once I start hearing those calls, I better start planning the field work season ahead.

The long weekend in October, that coincides with an end to the rugby league season, means field work planning should really be in full swing.

If these birds and farewell to footy season aren’t strong enough reminders, once daylight savings kicks in from early October, I know I’ve got to start moving!

In Sydney, “mosquito season” has historically run from the start of November through to the end of April. Field work is well underway by the time the Melbourne Cup is run and won.

One of the interesting trends in recent years has been are ever increasing early start to mosquito season. While the start of spring if often punctuated by occasional hot conditions, mosquitoes have usually be slow to kick into gear. It isn’t until late spring that serious pest problems are reported. However, in recent years, the start of the season has got earlier and earlier.

It is becoming so common to see boosts in mosquito numbers in late September and early October that start dates of mosquito control and surveillance programs are moving forward.

Say goodbye to summer holidays

My summers are dictated by tides and rainfall. These are the events that bring water into local wetlands and trigger hatches of mosquitoes. My schedule will shift from year with differences in the timing of king tides and the pattern of rainfall.

What these shifts in environmental conditions mean is that I can be in the wetlands on Christmas Day or New Years Eve. Sometimes mosquito season sucks.

The Australia Day holiday is often an important date, especially if it occurs just as mosquito populations are on the rise or there is increased activity of mosquito-borne pathogens. I’m often dealing with plenty of media enquiries at this time.

The kids are back in school by February and Sydney is well and truly out of holiday mode. For me, this means much earlier and later working times as I try to dodge peak-hour traffic getting from field site to field site. There is nothing more likely to take the gloss off some early morning time in the wetlands than spending twice as long as usually in crawling traffic as I try to get mosquitoes back to the laboratories.

Easter bunnies, chocolate eggs, and outbreaks of mosquito-borne disease

While it may be tempting to think the Easter Long-weekend may mark the end of the mosquito season and chocolate egg fueled celebrations can commence, it is important to keep in mind that Easter moves about from year to year. This can have important implications for mosquito monitoring and public health interventions.

When the Easter falls at the end of March or early April, there can be greater mosquito-borne disease risks. In many areas of Australia, mosquito-borne disease caused by Ross River virus is more commonly reported in autumn than summer or spring. Depending on the temperatures, tides, and rainfall, there can be very abundant populations of mosquitoes and elevated mosquito-borne disease risk just as everyone is taking off on long-weekend camping trips or school holidays. In 2020, with Easter falling in the middle or April, the risks shouldn’t be too high (but lets just wait to see what the weather and mosquito populations are like).

An end to daylight savings is usually a pretty good marker. I’m often caught out the first week after our clocks go back and need a head lamp or torch to finish setting mosquito traps! However, the real end point to mosquito season is typically ANZAC Day. While there may be some mosquitoes about through to the early stages of May, it is usually only under exceptional circumstances (at least around Sydney).

Bring on the cold (and report writing)

Between May and September, temperatures get too cold for mosquitoes to be a problem. It is the cold overnight temperatures (as opposed to the occasional warm daily temperatures) that influence mosquito populations. As soon as we start getting overnight minimums consistently dropping below 10oC, mosquito activity generally starts to decline.

Winter is spent writing, teaching, sleeping, conferences, planning, and trying to sneak in some kind of holiday….

If you’re a scientist, how do the seasons shift your schedule throughout the year? Join the conversation on Twitter!

 

 

 

Why has mosquito-borne disease hit Tasmania?

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Are there even mosquitoes in Tasmania?

You could be forgiven thinking that Australia’s southern most state, Tasmania, is probably free of mosquitoes and certainly the chances of an outbreak of mosquito-borne disease would be rare. Is it even possible?

Health authorities in Tasmania have recently warned residents and visitors to avoid mosquito bites following reports of locally acquired infections of Barmah Forest virus.

Ross River virus may be the best known of Australia’s local mosquito-borne pathogens but Barmah Forest isn’t far behind. Infection can cause an illness similar to Ross River virus disease, its typically marked by joint pain and inflammation, fatigue, rash, headaches, muscle pain, fever and chills.

Fortunately the disease is not fatal.

There have been outbreaks of Barmah Forest virus in many parts of Australia, not just in the tropical north. Significant outbreaks have occurred in NSW and southern Western Australia.

While Tasmania may be cold, that doesn’t mean there aren’t mosquito problems. There is a range of mosquitoes found in Tasmania, including Aedes camptorhynchus, a key species of pest and public health concern. This mosquito is closely associated with coastal estuarine wetlands, especially saltmarsh environments.

Tasmania has also had outbreaks of mosquito-borne disease. More than 100 people were infected with Ross River virus in the coastal region just to the east of Hobart in 2002. Specimens of Aedes camptorhynchus collected in the region tested positive to the virus making transmission risk most likely influenced by an abundance of this mosquito.

Like Ross River virus, Barmah Forest virus is spread by mosquitoes to people from local wildlife. It is likely that the virus quietly circulates between native animals, such as birds and mammals, but when favorable conditions for mosquitoes occur and populations increase, the risks of transmission to people increase.

While there is only a hand full of cases confirmed to date, a total of five with an additional two to be confirmed, it may not seem significant. However, it is a reminder that wherever mosquitoes, wetlands, and wildlife occur, there can also be a risk of mosquito-borne disease transmission.

With a warmer Tasmania possibly resulting from climate change and a concomitant extension of the “mosquito season” in coming years, perhaps the public health risks associated with mosquitoes will be something for health authorities to keep a closer eye on in the future. Importantly, is it time for local authorities to proactively monitor mosquitoes and the activity of mosquito-borne pathogens?

The image used at the top of this post comes from John Tann via Flickr; a mosquito (possibly Aedes alboannulatus) from Strahan, Tasmania.

Find out more about the amazing mosquitoes of Australia by picking up a copy of the award winning “A Guide to Mosquitoes of Australia” from CSIRO Publishing.

 

Mosquitoes feed on frogs, very small frogs…

I was excited to be asked back on the Science on Top podcast recently to record an episode about mosquitoes, currently declines in insect populations (are mosquitoes on the way out too?), and whether recent flooding in north QLD would result in increased mosquito populations and risk of mosquito-borne disease outbreak.

Please subscribe to the podcast, its a really fun and relaxed look at whats making headlines in the science world. The crew themselves describe the podcast as:

The Australian podcast about science, health and technology news. Join Ed Brown and his panel of co-hosts each week as we talk about the latest and coolest research and discoveries in the world of science. We’re joined by special guests from all over the science field: doctors, professors, nurses, teachers and more.

If you’re interested, you can chase up my previous guest spot with them talking “Everything Zika” back in 2016.

I still hold some aspirations of starting my own podcast. Problem is finding the time (there isn’t even enough time to catch up on my podcast “to do” list). Perhaps this is a project for the coming summer.

Would you listen to a podcast about mosquitoes and the people who study them?

You can catch up on a couple of other podcasts I’ve guested on over the past few years. Check out Flash Forward (The Ultimate Swatting) and Arthropod (Getting to Know Mosquitoes).

Oh, and mosquitoes do feed on frogs. Frog blood, not the whole thing. It would have to be a very small frog…

 

 

 

Are mosquitoes disappearing?

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There’s been a swarm of headlines recently about the global decline of insects. Could mosquitoes be disappearing too? Probably not but how would we know?

Recent research suggests that over 40% of insects worldwide are in decline. Some of the most vulnerable insects are those that occupy specific ecological niches. When scientists reviewed over 70 historical reports of insect declines, environmental degradation, the spread of agriculture, and widespread insecticide use were suspected for causing the decline.

What about mosquitoes? Sadly, they’re not a group of insects many people would care too much about if they were threatened with extinction.

Some of the most important mosquitoes, those that transmit dengue viruses or malaria parasites, are evading our efforts to eradicate them. For these insects, the insects authorities the world over actively are trying to kill, they’re surviving quite well. They’re becoming resistant to commonly used insecticides and they’re thriving living in habitats in and around our cities.

The reality is that some mosquitoes are probably doing very well , while those potentially under threat are probably those we know least about.

Tracking change in mosquito populations

There are over 300 mosquitoes in Australia. The mosquitoes that bring with them the greatest pest and public health risks are well studied. Mosquitoes such as Aedes camptorhynchus, Aedes vigilax, and Culex annulirostris are nuisance-biting pests and have been associated with outbreaks of Ross River virus disease. Their populations are monitored as part of mosquito control and surveillance programs around the country. But these programs probably won’t reliably pick up declines in lesser known mosquitoes.

There are mosquito surveillance programs around the country that provide information on local mosquito populations to health authorities. That’s how scientists know if this really is the “worst year for mosquitoes ever”! There is little evidence that the major pest mosquitoes are in decline. But these programs probably won’t reliably pick up declines in lesser known mosquitoes.

Mosquitoes under threat?

It is entirely possible that there are mosquitoes under threat.

What about the mosquitoes that specifically feed on frogs, how will they be impacted by declining frog populations?

Mosquitoes that are highly specialised to certain environments or ecological niches or close interactions with wildlife may struggle if their ecosystems are disrupted. Habitat degradation may hit some mosquitoes in much the same way it’ll hit other insects. It won’t end well.

What about mosquitoes associated with snow-melt pools in the Australian alps? Could climate change see their habitats destroyed?

Mosquitoes can adapt

Mosquitoes can be some of the most adaptable animals on the plant. That’s probably why they’ve been such persistent pests. In fact many insects are quite adaptable to change and that’s why we may not be facing an “insect apocalypse” as many headlines suggest.

We’ve found that mosquitoes are more abundant in mangrove forests that are degraded or surrounded by industry. Some mosquitoes are even becoming resistant to commonly used insecticides. Those same issues threatening many thousands of insects are no problem for some mosquitoes.

The reality is, mosquitoes have already been around for millions of years, they’ll probably be around long after. Its just that we could take a few species with us…

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The image at the top of this article is of a carbon-dioxide baited mosquito trap, there were thousands of mosquitoes inside; collected late in 2018 along the Georges River in southern Sydney.

Join the conversation on Twitter, are there any mosquitoes you think are under threat?

 

Giant mosquitoes are invading my backyard!

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“I’ve never seen anything like it. I actually heard it before I saw it!”

I get more than a dozen emails, tweets, or phone calls every summer like this. Excited (terrified?) correspondence asking about the “giant” mosquito captured in the backyard or buzzing about windows.

Toxorhynchites speciosus is as “good” a mosquito as there can be. First, it is a gorgeous creature. Almost four times the size of a typical mosquito, it is a large dark and shiny mosquito with bright metallic patterns.

There are around 70 species of Toxorhynchites mosquitoes around the world but only a few species found in Australia. The mosquito is reasonably common, but rarely very abundant. It is found along the eastern and north coast of Australia, stretching from Sydney through to Darwin.

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The larvae of Toxorhynchites speciosus are large and easily spotted in water-holding containers around the backyard

This is one of the few mosquitoes that don’t need blood. Unlike almost all other mosquitoes, the females of which need blood to develop their eggs, Toxorhynchites speciosus doesn’t bite. It gets its energy from plant juices and nectar.

Even though it doesn’t bite, the sheer size of this mosquito makes it an imposing sight.

They most commonly lay eggs in water holding containers around the home. Pot plant saucers, bird baths, watering cans, buckets, bins and even tree holes and water-filled bromeliads. These are the same types of water-filled containers where you’ll find wrigglers of the pest mosquitoes Aedes notoscriptus and Culex quinquefasciatus.

They have a fascinating way of laying eggs. Unlike many other mosquitoes that elegantly stand on the water surface and lay up to 300 eggs in a neatly packed floating raft, Toxorhynchites lays single eggs. It  doesn’t even land on the water to lay eggs, it fires them into water while in mid flight!

Once an appropriate place to deposit an egg has been identified, the mosquito flies in a vertical loop, the loops getting ever smaller until the egg is ejected and into nearby habitats. A neat trick and avoids the risk of being eaten by a hungry spider or other predator waiting by to grab a mosquito coming in to lay eggs.

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A specimen of Toxorhynchites speciosus collected by Helen Mamas from the inner west suburb of Sydney, Newtown

Not only do these mosquitoes not bite, they even help out with a little pest mosquito control around the home.

While the mosquito wrigglers of mosquito mosquitoes feed on organic debris floating about in water bodies, the larvae of Toxorhynchites speciosus are predatory and feed on the wrigglers of other mosquitoes. Laboratory studies have shown that a closely related Toxorhnychites consumed over 300 Aedes aegypti  (aka the dengue mosquito) larvae during its development. In some parts of the world, a closely related mosquito is used as a biological control agent of the pests that spread dengue, chikungunya and Zika viruses.

While Toxorhynchites speciosus will chomp through plenty of wrigglers of Aedes notoscriptus each summer in Australian backyards, it is unlikely to make a huge difference in bites.

My experience in backyards across Sydney has shown that there is something of a tug-o-war between Toxorhynchites speciosus and other mosquitoes. While undertaking a project with Ku-ring-gai Council looking at backyard mosquitoes and their possible impact on backyard wildlife conservation efforts, I’d often find a fluctuating dynamic between the mosquito predators and their prey. Populations of Aedes notoscriptus or Culex quinquefasciatus would build up in bird baths and buckets, then Toxorhynchites speciosus would move in. They’re eat through all the other larvae, then once emerged and flown off, the other mosquitoes would move back in. And the cycle continued.

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Image of Toxorhynchites speciosus sent to be by David Lawson from the inner west suburbs of Marrickville, Sydney.

Next time you see a “giant mozzie” buzz by, think twice before you squish it. Oh, and keep in mind that this mosquito is also a movie star! Do you recognise it from Jurassic Park?

If you want to keep the pest mosquitoes out of your backyard, make sure you get rid of any water-holding containers. If you can’t throw them out, keep them covered.

Check to make sure your roof gutters and drains are clear of leaves and other debris so they flow freely. Check your rainwater tank is screened to stop the mozzies entering. And try not to kill the good guys who help keep the other mozzies at bay!

For more on how to better control insect pests in and around the home, read one of our latest publications on engaging urban stakeholders in the sustainable management of arthropod pests.

Find out more about Australia’s fascinating mosquitoes by checking out our “A Guide to Mosquitoes of Australia” via CSIRO Publishing!

 

Wetlands, climate change, and managing mosquitoes

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I’ve spent over twenty years sloshing about in wetlands around Sydney and surrounds. They’re changing. They’re changing due to shifts in climate, sea level rise, and urbanisation. The 2019 World Wetlands Day is a time to stop and reflect on the state of wetlands around the world and how we can keep them health under the threat of climate change.

World Wetlands Day is held every year on 2 February,  this day marking the adoption of the Convention on Wetlands on 2 February 1971 in Ramsar, Iran. The theme of the 2019 World Wetlands Day is “Wetlands and Climate Change” and we shouldn’t just think about the impact of climate change on wetlands but also how wetlands can help us as we face the challenges of a changing climate.

Coastal wetlands around Sydney are impacted in many ways. Mangrove forests and saltmarshes are degraded through direct and indirect human activity. There is recent research indicating that sea level rise is impacting mangroves along the Parramatta River in Sydney. This requires active management to ensure substantial degradation and die back occurs, as has been seen elsewhere in Australia.

Some of our research even suggests that degraded mangroves are more productive when it comes to mosquitoes. Effective rehabilitation of these habitats may actually reduce the mosquitoes flying out of these environments and impacting the community nearby. Similarly, urban planning should consider the risk posed by mosquitoes in wetlands adjacent to new and expanding residential developments. This includes major wetland rehabilitation projects.

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The challenges facing wetlands isn’t unique to Australia. Released in conjunction with World Wetlands Day preparations was The Global Wetland Outlook. A document that provides “a current overview of global wetlands: their extent, trends, drivers of change and the responses needed to reverse the historical decline in wetland area and quality”.

While we think of rainforests and coral reefs under greatest threat, it is a sobering thought to think that up to 87% of the global wetland resource has been lost since 1700. These are environments that were, until relatively recently, considered wastelands. With this lack of perceived value came greater susceptibility to abuse and degradation.

Along with the unsurprising loss of wetland area and decline in biodiversity associated with these environments come some interesting findings. The most interesting from a mosquito management point of view is that artificial wetlands are actually increasing in some areas. Notwithstanding an assessment of the ecosystem services they provide, they’re more likely to be closer to human habitation, so any mosquitoes associated with them may have relatively greater impact.

In recent years, the value of wetlands has increased. There is an understanding now that these environments provide critical ecosystem services. There is also a growing understanding of the wetland’s roles in mitigating the impacts of climate change. Coastal wetlands in particularly provide protection from increasingly severe storm events and trap valuable carbon stores that assist in mitigating the impacts of climate change.

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This then raises the issues of mosquitoes. Mosquitoes are a natural part of wetland ecosystems. While often their pest impacts may indicate the poor health of the wetlands, at other time, abundant mosquito populations are a natural occurrence that fluctuate in their intensity from year to year. How do best manage mosquitoes associated with these wetlands?

I’ve written about how I think mosquito control should actually be considered an important component of coastal wetland rehabilitation. How climate change may be impacting mosquito threats and that even hot and dry summers under the influence of El Nino may not necessarily mean that mosquitoes are less problematic.

Based on the experience during the 2018-2019 summer, mosquitoes seem to persist in plague proportions despite the extreme temperatures being experienced in NSW.

It is important to remember that there are many mosquito species associated with wetlands, especially freshwater habitats, that pose no substantial threat to humans. There are hundreds of mosquitoes in Australia, less than a dozen really pose a substantial pest or public health threat. Many mosquitoes may play an important ecological role in wetland ecosystems. This may include representing a locally important food source for insectivorous wildlife or possibly pollinating plants.

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A balance is required. If we’re going to continue squeezing an increasing human population into a narrow stretch of land up against the coast, there are many issues to consider here and they’re not just about how human activity is impacting those coastal wetlands. Pollution is a problem, our physical damage is another. Worst still, we’re taking away the opportunity of these normally resilient habitats to adapt to a rising sea levels and increasingly frequent storm events. Our cities and their infrastructure provide a hard and unforgiving edge against the wetlands.

Our wetlands even battle against themselves sometime. The threat of mangrove incursion into saltmarsh habitats is of increasing concern. Its counter-intuitive but perhaps we need to be pulling out mangroves to save some coastal wetlands.

Expanding, modifying, and creating new coastal wetlands will require local authorities to turn their mind to the issue of mosquitoes. Firstly, consideration needs to be given to what may constitute a tolerable level of mosquito exposure. How many mosquito bites are too many? How many cases of mosquito-borne disease are considered “normal” each year. Once these thresholds are drawn and exceeded, who is responsible for the decisions on active mosquito control? Who pays?

Another ecosystem disservice to consider is how the nuisance-biting of mosquitoes may discourage engagement with local wetlands. less engagement may mean less support for conservation and rehabilitation efforts. Less community interest, support, and activism may then result is less political drive to protect local wetlands by local authorities.

Importantly, decisions regarding the management of coastal wetlands, as well as those peppered throughout the city, need to be made with some consideration of mosquitoes and their potential impact. How do you convince the local community about the overall benefits of carbon sequestration, wildlife conservation, and protection of infrastructure is worthwhile if their quality of life is degraded through summer swarms and nuisance-biting mosquitoes?

More details on managing the risks associated with estuarine mosquitoes is provided in this book chapter included in the free Sydney Olympic Park Authority’s guide to managing urban wetlands.

For more about World Wetlands Day activities in Australia see here.

To stay up to date with my adventures in local wetlands, you can follow me on Instagram here.

 

 

 

Preparing for the exotic mosquito invasion of Australian backyards

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While Australia has hundreds of “home-grown” mosquitoes, it is just a few from overseas that have authorities on alert. Preparing for these new risks is critical if the future pest and public health risks associated with mosquitoes are to be effectively managed. Citizen scientists may hold the key to success!

A project underway in the Northern Rivers region of NSW is set to build a framework for responding to the threats of exotic mosquitoes. This is in association with the Building Resilience to Climate Change program, a partnership program between Local Government NSW (LGNSW) and the NSW Office of Environment and Heritage (OEH) to address identified climate change risks and vulnerabilities facing NSW councils.

Lead by Tweed Shire Council, the program “Developing and trialing a Northern Rivers Emerging Vector Response Plan” is designed to build capacity among local stakeholders in the region to better respond to possible introductions of exotic mosquitoes from overseas (or perhaps travelling south from Queensland).

The mosquitoes that pose the greatest risk are Aedes aegypti and Aedes albopictus. As well as being severe nuisance-biting pests, these mosquitoes can transmit pathogens of serious public health concern such as Zika, dengue and chikungunya viruses. The mosquitoes aren’t found in local wetlands, they prefer backyard water-holding containers. This means that should these mosquitoes make their way to NSW, local authorities must shift their focus from the swamps to the suburbs.

There is already a program in place monitoring mosquitoes and the pathogens they carry in NSW. This program is primarily focused on Ross River virus and the mosquitoes that transmit this pathogen. As a consequence, mosquito collections are typically in bushland or wetland areas adjacent to urban areas and may not readily pick up exotic mosquitoes that have moved into local backyards.

Authorities must expand their approach and develop strategic responses to these exotic threats.

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Representatives of local stakeholders help survey 300 backyards in Tweed Heads!

This work is already underway. A workshop for local stakeholders was held in December 2017 in Tweed Heads along with a two day field exercise in which around 300 residential backyards were surveyed for potential mosquito habitats. A wide range of potential sources of mosquitoes was identified, the most common were water-filled plants (particularly bromeliads), pot-plant saucers, buckets, wheel burrows, garden ornaments, and rainwater tanks.

The survey highlighted how important community involvement in the program is and “citizen science” is currently being employed to assess some mosquito surveillance technologies in backyards across the Tweed Heads region.

Supported by a grant from the Human Health and Social Impacts Node, a partnership between the Office of Environment and Heritage, NSW Health and The University of Sydney, over 150 mosquito traps were deployed and it is hoped that the mosquitoes they collect will help inform the development of strategic mosquito surveillance in the future.

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An example of the mosquito traps deployed across two suburbs in Tweed Heads to collect eggs from mosquitoes buzzing about backyards

Whats needed now is a better understanding of how the community thinks about mosquitoes and how they’re trying to make their backyard less favourable for these pests.

Residents in the Local Government Areas of Tweed, Byron, Ballina, Richmond Valley, Clarence Valley, Lismore and Kyogle are invited to participate in a short survey. It is a great way to learn how to reduce the risks of mosquito bites in your backyard (there is also an iPad that can be won!).

If you live in the areas mentioned, or know friends or family who do, please complete and/or share the details of the survey.

You can start the survey now!

There are many factors contributing to the future threat of  mosquitoes and mosquito-borne disease in Australia. Climate change or exotic mosquito introductions may be game changes but one of the most important considerations is the importance of community awareness and willingness to assist local health authorities.

Perhaps the new mosquito emoji will help too?