Preparing for the exotic mosquito invasion of Australian backyards


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.


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.


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?







A flood of festive season media coverage


Spring is gone and with the arrival of summer comes the mosquitoes. Calls from the media inevitably follow shortly after. I have no doubt many journalists, broadcasters and producers have my name in their diaries, circled brightly in red, on the first day of summer!

It is a fun part of my job to deal with the media. Its more than just getting a chance to talk about mosquitoes and their role in the local environment, it also provides an opportunity to do some important public health communications around the issues of mosquito bite prevention and management of mosquito-borne disease.

Scorchers, sun protection, and buzzing bloodsuckers

What got the ball rolling this year was a joint media briefing arranged by ausSMC. Alongside colleagues talking about heat waves, summer storms, sun protection and bushfire, I shared some tips on protecting yourself from mosquito bites and mosquito-borne disease this summer. It was interesting speaking alongside Professor Sanchia Aranda, CEO of Cancer Council Australia, and comparing the ways we promote safe and effective use of sunscreens and mosquito repellents. This was picked up on in additional media coverage. Overall, there was over 300 local and international articles following this media briefing!

The briefing provided an opportunity to fill a gap in public health communication I’ve identified (and tried to fill) in recent years. Health authorities are pretty good at providing advice on choosing mosquito repellents but less so on using them effectively. Ensuring repellents are actually used effectively is the best way to increase the protection of the community against mosquito-borne disease.

In early December we held our “Sydney Ideas: Mosquitoes in the City” event at Westmead. This was a great opportunity to speak to the community and the well attended event prompted some broader interest in the work of presenters.

It was a pleasure being able to visit the studios of ABC Radio National with Prof Tony Capon, Professor of Planetary Health at the University of Sydney, to discuss with Philip Adams how urbanisation and a changing climate may influence local mosquito populations and mosquito-borne disease risk. I’m working more and more with Tony so nice to share the opportunity to talk about this initiative with him on national radio. You can listen back here. This work is strongly linked to the theme of the “Mosquitoes in the City” event and there is clearly much to learn regarding the place of mosquitoes, wetlands, wildlife and mosquito-borne disease at the fringes of our metropolitan regions under the influence of a changing climate and the ways urban design responds to the threat.



Why me? I wish mozzies would bite my friends instead!

There was another boost in interest resulting from a spot on ABC News 24 Weekend Breakfast. The accompanying online article explaining why mosquitoes are more likely to bite some people more than others then sparked considerable interest! What followed was a bunch of radio and television interviews.

There was also a follow up article at and this was also picked up on “Kids News” who republished a modified version of the story together with some suggestions for classroom learning exercises. Nice.

There were two different experiences with ABC News. The appearance on Weekend Breakfast was great. I’ve done segments with Andrew Geoghegan and Miriam Corowa before, have always been impressed with their knowledge and interest. I really enjoy the relaxed feel on the show. Was also a pleasure working with Dale Drinkwater, the producer, who put together the segment and accompanying article.

A couple of days later I appeared on News Breakfast with Virginia Trioli. As the program is produced out of Melbourne, I had to do a live cross from the Sydney studios. I always find these interviews a little uncomfortable as I’m tucked away in a small, dark recording booth staring down a camera and hoping my ear piece doesn’t fall out! I’m sure there is an art to these but I’m not sure I’ve mastered that just yet.


Once the mozzies start biting…

With the warm weather arriving and everyone’s minds turning to summer, there is always a flood of festive season-related media stories. Once the mozzie stories started popping up, many more media outlets starting running segments.

There were also warnings about the health threats of mosquitoes over the festive season from local health authorities.

I had the chance to visit many radio and television studios to conduct interviews, this time it was the first opportunity to visit the Macquarie Radio (home to 2UE and 2GB) for what turned out to be a relatively long (by commercial radio standards) interview with Tim Webster on Talking Lifestyle/2UE including a few callers asking about mosquito repellents, disease risk and what the “purpose” of mosquitoes actually is! Listen back via the Holiday and Home podcast.

Taking talkback can be tricky. I’m fortunate enough to have had an opportunity to do this reasonably routinely. I appreciate the opportunity to get a feel for what the community wants to know about mosquitoes, we should be taking these things into account when designing fact sheets and other communication material. There is no point in simply systematically repeating what has come before.

Live TV can also be tricky. I also had the chance to do segments on Channel Nine’s Today and Today Extra programs. These are always fun and I do find it fascinating to see how the behind-the-scenes production of these shows get put together.

Even the local newspaper, the Parramatta Sun, ran a nice story with great shot of me among the mangroves of the Parramatta River. It is also fun dragging photographers out into the wetlands. This time a fun shot of me from a different perspective other than simply standing beside a mosquito trap!


There was certainly plenty of “buzz” (or should that be “hum”) about mosquitoes over recent weeks. Great to see other articles pop up by fellow science communicators as well as the occasionally celebrity. There can never be too many ways to get the message out!

The mosquito coil conversation

At the point where I thought everyone was getting sick of mosquitoes, my latest article on the safe and effective use of mosquito coils was published at The Conversation (as well as being republished by ABC News). To date there have been about 90,000 clicks on the article, highlighting just how interested people are in the topic.

There were a bunch of other interview requests on the back of this including ABC Sydney, ABC Brisbane and ABC Adelaide. You can listen back to my chat with James Valentine on ABC Nationwide Afternoons here.

It isn’t always easy managing media requests

To finish up, I think it is important to share some of the reality of wrangling all these media requests. Most importantly, it takes time. It takes time to prepare and it takes much more time to actually do these activities.

For live television appearances, that often only last a few moments, you’re typically asked to arrive at the studios 30-40min prior to scheduled interview. Notwithstanding the travel time back and forth from studios (often very early in the morning), this means the interruption to the day isn’t insignificant. There was one day that I participated in two different teleconferences while in transit to and between interviews at ABC in Ultimo and Channel Nine in Willoughby!

The other thing is that sometimes you’ll get bumped. I was scheduled to chat on a live television program that requested I bring along a cage of live mosquitoes. This is generally not a problem but it does take time, especially when I have to actually collect field caught mosquitoes especially for this purpose. Unfortunately, the segment got bumped on one day, rescheduled for the next and then bumped again for a second time.

It would be easy to get really upset in these circumstances but it is a reality of dealing with the media. Don’t take it personally as these things are mostly out of your control. If you’re keen to engage with the media, this is just one of the many challenges you’ll need to learn to manage.

Spot any other cool mozzie media things? Join the conversation on Twitter or Facebook!


Why do mosquitoes seem to bite some people more?

Back in 2015, I had an article published at The Conversation on why some people are more likely to be bitten by mosquitoes than others. It is one of the most commonly asked questions I get whenever I give public talks (or friends and family are quizzing me at summer BBQs).

This article was incredibly successful and has currently been read by approximately 1.4 million people. That is a lot of people. Hopefully the science of mosquito bites has got out there and actually helped a few people stop themselves or their family being bitten by mosquitoes!

The warm weather is starting to arrive here in Australia so I am sharing this once more for those wondering why they’re always the “mosquito magnet” among their friends…

Health Check: why mosquitoes seem to bite some people more

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There are up to 400 chemical compounds on human skin that could play a role in attracting mosquitoes.  sookie/Flickr, CC BY-SA

There’s always one in a crowd, a sort of harbinger of the oncoming mosquito onslaught: a person mosquitoes seem to target more than others. What is it about these unlucky chosen few that makes them mosquito magnets?

There are hundreds of mosquito species and they all have slightly different preferences when it comes to what or who they bite. But only females bite; they need a nutritional hit to develop eggs.

Finding someone to bite

Mosquitoes are stimulated by a number of factors when seeking out a blood meal. Initially, they’re attracted by the carbon dioxide we exhale. Body heat is probably important too, but once the mosquito gets closer, she will respond to the smell of a potential blood source’s skin.

Studies have suggested blood type (particularly type O), pregnancy and beer drinking all make you marginally more attractive to mosquitoes. But most of this research uses only one mosquito species. Switch to another species and the results are likely to be different.

There are up to 400 chemical compounds on human skin that could play a role in attracting (and perhaps repulsing) mosquitoes. This smelly mix, produced by bacteria living on our skin and exuded in sweat, varies from person to person and is likely to explain why there is substantial variation in how many mozzies we attract. Genetics probably plays the biggest role in this, but a little of it may be down to diet or physiology.

One of the best studied substances contained in sweat is lactic acid. Research shows it’s a key mosquito attractant, particularly for human-biting species such as Aedes aegypti. This should act as fair warning against exercising close to wetlands; a hot and sweaty body is probably the “pick of the bunch” for a hungry mosquito!

Probably the most famous study about their biting habits demonstrated that the mosquitoes that spread malaria (Anopheles gambiae) are attracted to Limburger cheese. The bacteria that gives this cheese its distinctive aroma is closely related to germs living between our toes. That explains why these mosquitoes are attracted to smelly feet.

But when another mosquito (such as Aedes aegypti) is exposed to the same cheese, the phenomenon is not repeated. This difference between mosquitoes highlights the difficulty of studying their biting behaviours. Even pathogens such as malaria may make us more attractive to mosquitoes once we’re infected.

Only females bite because they need a nutritional hit to develop eggs.
Sean McCann/Flickr, CC BY-NC-SA

Researchers are trying to unscramble the irresistible smelly cocktails on the skins of “mosquito magnets”. But the bad news is that if you’re one of these people, there isn’t much you can do about it other than wearing insect repellents.

The good news is that you may one day help isolate a substance, or mixes of substances, that will help them find the perfect lure to use in mosquito traps. We could all then possibly say goodbye to topical insect repellents altogether.

Attraction or reaction?

Sometimes, it’s not the bite as much as the reaction that raises concerns. Think of the last time the mosquito magnets in your circle of friends started complaining about being bitten after the event where the purported mosquito feast took place. At least, they appear to have attracted more than the “bite free” people who were also at the picnic, or concert or whatever.

But just because some people didn’t react to mosquito bites, doesn’t mean they weren’t bitten. Just as we do with a range of environmental, chemical or food allergens, we all differ in our reaction to the saliva mosquitoes spit while feeding.

People who don’t react badly to mosquito bites may think they haven’t been bitten when they’ve actually been bitten as much as their itchy friends. In fact, while some people attract more mosquito bites than others, there’s unlikely to be anyone who never, ever, gets bitten.

The problem is that people who don’t react to mosquito bites may all too easily become complacent. If you’re one of them, remember that it only takes one bite to contract a mosquito-borne disease.

Finally, there is no evidence from anywhere in the world that there is something you can eat or drink that will stop you being bitten by mosquitoes. No, not even eating garlic, or swallowing vitamin B supplements.

The ConversationPerhaps if we spent as much time thinking about how to choose and use mosquito repellents as we do about why mosquitoes bite our friends and family less than us, there’d be fewer bites all around.

Cameron Webb, Clinical Lecturer and Principal Hospital Scientist, University of Sydney

This article was originally published on The Conversation. Read the original article.



Ross River virus in Melbourne, how did that happen?


Health authorities in Victoria have been warning of mosquito-borne Ross River virus for much of the summer. The state is experiencing one of its worst outbreaks of the disease but cases have mostly been across inland regions. Now it’s hit Melbourne. How has this happened?

Ross River virus is the most commonly reported mosquito-borne disease in Australia. There are usually about 5,000 cases across Australia. However, in 2015 there was a major spike in activity with around 9,000 cases reported. It is a common misconception that the disease is only found in northern regions of Australia. I’m often told “I heard the disease is moving south from QLD?” That’s not the case.

The virus is just as much a natural part of the Australian environment as the mosquitoes and the wildlife that maintain transmission cycles.

While there are generally more cases in northern Australia, nowhere is safe. Some of the largest outbreaks have occurred in southern regions of Western Australia, South Australia, Victoria and even Tasmania.

The virus is widespread but is generally associated with rural regions. A driving factor in determining the activity of Ross River virus is that more than just mosquitoes are involved in outbreaks. The virus is maintained in the environment in native wildlife, especially kangaroos and wallabies. Even when and where there are high numbers of mosquitoes, without wildlife, outbreak risk is low. This is the reason why any clusters of locally infected cases in metropolitan regions are typical in areas where there are wetlands, wildlife and mosquitoes occurring together. We’ve seen this on the urban fringe of Sydney and Perth in recent years.

The announcement of locally acquired cases in the suburbs of Frankston and Casey, in Melbourne’s south-east, has taken many by surprise. Should it have?

Victoria is no stranger to mosquitoes and outbreaks of mosquito-borne disease. There are mosquito surveillance and mosquito control programs in place in many regions and historically there have been major outbreaks of mosquito-borne disease. From freshwater flood plains of the inland to the tidally flooded estuarine wetlands of the coast, Victoria has diverse and often abundant mosquitoes. But cases in the metropolitan region are rare.

Victorian mosquitoes are not all bad but over a dozen different mosquito species can spread Ross River virus.

The region where these cases have been identified are in proximity to bushland and wetland areas. There is no doubt plenty of mosquitoes and suitable wildlife too. While this is the first time local transmission has been documented, that doesn’t mean the virus hasn’t circulated in the past, or even that cases may have occurred.

For individuals infected but only suffering mild symptoms, the illness can be easily discounted as nothing more than a mild case of the flu. Without appropriate blood tests, these cases never appear in official statistics. For this reason, many mosquito researchers believe that the number of notified cases across the country is just the tip of the iceberg with many milder infections going diagnosed.

But why in Melbourne now?

It is difficult to know for sure. The two most likely explanations are that either environmental conditions were ideal for mosquitoes and suitable populations of wildlife were present so that the virus was much more active in the local environment than previously. The second explanation is that the virus may have been introduced to the region by a traveller or movement of wildlife. In much the same way Zika virus made its way from SE Asia to South America in the last few years, mosquito-borne viruses move about in people and animals, much less so than mosquitoes themselves (but that isn’t impossible either).

Victoria (as well as inland NSW) is experiencing one of its largest outbreaks of Ross River virus on record following significant flooding of inland regions. With so much activity of the virus in the region, perhaps an infected bird or person travelling to the metropolitan region brought the virus with them. When bitten by local mosquitoes, the virus started circulated among local mosquitoes and wildlife.

Most people infected by Ross River virus are bitten by a mosquito that has previously fed on a kangaroo or wallaby.

Once it’s made its way to metropolitan regions, the virus can be spread from person to person by mosquitoes. Common backyard mosquitoes, especially Aedes notoscriptus, can transmit the virus but as these mosquitoes are not particularly abundant, don’t fly vary far and will just as likely bite animals as humans, they’re unlikely to drive major urban outbreaks of the disease. This mosquito doesn’t pack the same virus-spreading-punch as mosquitoes such as Aedes aegypti that spreads dengue, chikungunya and Zika viruses. Aedes aegypti isn’t in Victoria.

We’re unlikely to see significant spread of Ross River virus across Melbourne but that doesn’t mean Victorians should be complacent. As there is no cure for Ross River virus disease, the best approach is to avoid being infected in the first place. Preventing mosquito bites is the best approach. For my tips and tricks on avoiding mosquito bites see this recent paper in Public Health Research and Practice as well as my article for The Conversation.

Keep an eye on the website of Victoria Health for more information.







West Aussies versus the local mozzies

This is a special guest post from Dr Abbey Potter, Senior Scientific Officer, Environmental Health Hazards, WA Health. I’m currently mentoring Abbey as part of The Public Health Advocacy Institute of WA (PHAIWA) Mentoring Program. Its been a great experience as we navigate through some of the strategies to raise awareness of mosquito-borne disease and advocate for better approaches to addressing the public health risks associated with mosquitoes.


Living in WA, we’re all too familiar with the pesky mosquito. We know they bite but what we often don’t consider is that they can transmit serious and sometimes deadly diseases. In fact, a recent survey of locals indicated that knowledge of mosquito-borne disease is pretty limited, particularly among younger adults aged 18-34 years and those living in the Perth Metro. It’s pretty important we’re aware of the risks posed by these pint-sized blood suckers and how you can avoid them… and here’s why!

The Facts

On average, more than 1,000 people will be infected with a mosquito-borne disease in WA every year. Our mossies can transmit Ross River virus, Barmah Forest virus, West Nile virus (Kunjin substrain) and Murray Valley encephalitis virus. All four cause diseases that are debilitating at best, causing weeks to months of symptoms. Murray Valley encephalitis is limited to the north of the State but is so serious it can result in seizures, coma, brain damage and even death.

Forget the bush, most people bitten in their own backyard. West Aussies are all very prone to getting eaten alive while socialising outdoors but if you’re up in the north of the State, you’ve also got a much higher likelihood of being bitten while boating, camping or fishing or working outside, compared to the rest of the state.

And don’t think you’re off the hook when you head off on holidays. A further 500 WA residents return from overseas travel with an exotic mosquito-borne disease every year. Heading to Bali? Beware of dengue, especially young adult males who return home with the illness more than others. There is limited mosquito management in many overseas countries where disease-transmitting mozzies can bite aggressively both indoors and throughout the day. This catches West Aussies off guard, as we are accustomed to mozzies biting outdoors, around dusk and dawn. When you’re in holiday mode it’s likely that you’ll be relaxing, having a couple of drinks and not thinking about applying repellent. Oddly enough, mosquitoes may actually be more attracted to people whose body temperature is higher. This happens naturally when you consume alcohol, so best pull out the repellent before you crack your first beer.

Despite our attractiveness to mosquitoes, we aren’t really aware of the most effective ways to avoid bites or how we can do our bit to reduce breeding in our own backyards. If you live by the mantra Cover Up. Repel. Clean Up you’ll have no problems!


Western Australia has some amazingly beautiful wetlands but these saltmarshes around Mandurah can produce large populations of nuisance-biting mosquitoes!

Cover Up

If you know you are going to be outdoors when mosquitoes are active, wear loose, long-fitting clothing that is light in colour. Believe it or not, mosquitoes can bite through tight pants as tough as jeans – I’ve witnessed it!

If you’re staying in accommodation that isn’t mosquito-proof, consider bed netting.

Try to keep children indoors when mosquitoes are most active. If exposure can’t be avoided, dress them appropriately and cover their feet with socks and shoes. Pram netting can also be really useful.

Admittedly, it’s not always practical to wear long sleeves during our warm summer nights, so there are going to be times when you need to use repellent. Choose a product that actually works and apply it appropriately so it does the job. Despite our best intentions, this is where we often go wrong. There are a few basic things to cover here, so stick with it!

Ingredient: Science tells us that the best active ingredient for repelling mosquitoes is diethyltoluamide (DEET for short) or picaridin. You need to look for either one of these names on the repellent label under the ‘active constituents’ section.

Unfortunately, natural repellents and anything wearable (e.g. bands, bracelets or patches) have very limited efficacy. Experts don’t recommend you use them and I consider this very wise advice. It only takes a single mosquito bite to become infected and chances are you will receive at least one if you rely solely on a product of this nature. It just isn’t worth the risk.


Percentage: The next thing to consider is the percentage of the active ingredient. This can range anywhere from 7% to 80% which can make choosing a repellent confusing. Just remember, the higher the percentage, the LONGER the product will remain active for. It doesn’t mean it will repel mosquitoes better.

A repellent containing 16-20% DEET will provide around 4-6 hours of protection, and is a good place to start. Repellents labelled ‘tropical strength’ usually contain greater than 20% DEET – they are useful when you spend longer periods exposed to mosquitoes or if you are heading to a region where dengue, malaria or Zika is problematic. Kids repellents usually contain picaridin or <10% DEET.

Sometimes it can be tricky to work out the percentage of the active ingredient. You can see the Bushmans example below states this clearly, but the other bottles list the ingredient in grams per litre (g/L). No need for complex maths – just divide by 10 and you have the magic number! For example, the RID label below reports the product contains 160g/L of DEET. This would convert to 16% DEET – easy!

You can see a few examples here of effective repellents:


How to Apply: No doubt we would all prefer if repellents didn’t feel quite so gross on our skin or didn’t smell so bad. Even I have to admit that before I moved into this field, I was guilty of putting just a dab here and a dab there. Unfortunately, this is flawed logic that will only result in you being bitten!

Repellents must be applied correctly to be effective. That means reading the label and applying it evenly to all areas of exposed skin. Remember to reapply the product if you are exposed to mosquitoes for longer than the repellent protects you for. You’ll also have to reapply the repellent after sweaty activity or swimming.

For more information on repellent use in adults and children, click here.

Clean Up

Mosquitoes need water to breed, but only a very small amount. Water commonly collects in a range of things you may find in your backyard including pot plant drip trays, toys, old tyres, trailers and clogged up gutters. Mosquitoes also love breeding in pet water bowls, bird baths and pools if the water is not changed weekly or they are not well maintained. Rain water tanks can also be problematic so place some insect proof meshing over any outlets. When you’re holidaying, cover up or remove anything that may collect water.


If you need more official info from WA Health about mosquito-borne disease or simple ways to prevent being bitten click here. And if you want to read more about how much West Aussies know (or don’t know) about mossies, check out Abbey’s excellent paper here! Joint the conversation too on Twitter by following Abbey and Cameron.


Preserve and protect? Exploring mosquito communities in urban mangroves


This is a special guest post from Dr Suzi Claflin. Suzi found herself in Sydney, Australia, (via Cornell University, USA) in 2015 to undertake a research project investigating the role of urban landscapes in determining mosquito communities associated with urban mangroves. She was kind enough to put this post together to celebrate the publication of our research in Wetlands Ecology and Management!


Sometimes you’ve got to make hard choices for the greater good. These situations can arise anywhere, but here – as usual – we are concerned with mosquitoes. There’s a balancing act carried out by public health officials and wetland managers trying to both preserve endangered habitat and protect human health. In this guest post, I’ll explain the science behind research I recently published in collaboration with Dr Cameron Webb, and suggest one way forward for addressing human and environmental health concerns in urban wetlands.

During my PhD, I studied how the landscape surrounding small-scale farms affects the spread of a crop virus and the community of insect pests that carry it. When I came to Australia to work with Cameron, I was surprised to find myself applying the same type of landscape ecology to mosquitoes and mangroves in urban Sydney.

The misfortune of mangroves

Mangroves are real team players. They provide a range of services to the surrounding ecosystem and to the humans lucky enough to live near them. Mangroves are extremely effective at protecting the shoreline (but this can sometimes be a problem). They prevent erosion by gripping the soil in their complex root systems and buffer the beach by serving as a wave break. By filtering sediment out of the water that flows over them, mangroves also prevent their neighbouring ecosystems, such as coral reefs and seagrass forests, from being smothered.

Despite all their good work, mangroves have an almost fatal flaw; they prefer waterfront property. Unfortunately for them, so do humans. Urban and agricultural development has eaten away at mangroves, leaving them highly endangered.

The mosquito menace

Mozzies are a public health menace, because they spread human diseases like Ross River virus (RRV). Because of this, public health officials rightly spend time considering how to supress mosquito populations in order to reduce the risk of disease transmission.

Here’s where things get tricky: mangroves are great for mosquitoes.

That leaves public health officials and wetland managers in a difficult position. On the one hand, mangroves are delicate, at-risk ecosystems that need to be preserved. On the other, mangroves and surrounding habitats potentially harbor both the animal carriers of the RRV (e.g. wallabies) and a load of mosquitoes, which means that people nearby may need to be protected.

How can we do both?



Dr Suzi Claflin trapping mosquitoes in the mangroves along the Parramatta River, Sydney, Australia.


The potential power of prediction

This is a hard question to answer. One approach is prediction: using measurements of the environment, like rainfall and tide level, to estimate what the mosquito community will look like in a given region. The mosquito community determines what management actions, like spraying an insecticide, need to be taken, based on the threat it poses to public health.

We set out to explore how the way we use land (e.g. for residential areas or industrial areas) near urban mangroves affects the mosquito communities that live in those mangroves. The project involved dropping over retaining walls, slipping down banks, and tromping through muddy mangroves along the Parramatta River in Sydney. We set mosquito traps (billy cans of dry ice with a container on the bottom) and left them overnight to capture the mozzies when they are most active. We did this at two points in the summer, to see if there was any change over time.

We found that yes, the way we use land around a mangrove makes a difference. Mangroves with greater amounts of bushland and residential land in the surrounding area had fewer mosquitos, and fewer species of mosquitos. On the other hand, mangroves with greater amounts of industrial land surrounding them had a greater number of mosquito species, and those surrounded by greater amounts of mangrove had more mosquitos.

And, just to muddy the waters a bit more (pun intended), several of these relationships changed over time. These results show that although prediction based on the surrounding environment is a powerful technique for mangrove management, it is more complicated than we thought.

Another way forward: site-specific assessments

Our work suggests another way forward: site-specific assessments, measuring the mosquito community at a particular site in order to determine what management approaches need to be used. This is a daunting task; it requires a fair number of man-hours, and mangroves are not exactly an easy place to work. But it would be time well spent.

By assessing a site individually, managers can be confident that they are taking the best possible action for both the mangroves and the people nearby. It turns out that the best tool we have for striking a balance between environmental and public health concerns, the best tool we have for preserving and protecting, is information. In mangrove management—as in everything—knowledge is power.

Check out the abstract for our paper, Surrounding land use significantly influences adult mosquito abundance and species richness in urban mangroves, and follow the link to download from the journal, Wetlands Ecology and Management:

Mangroves harbor mosquitoes capable of transmitting human pathogens; consequently, urban mangrove management must strike a balance between conservation and minimizing public health risks. Land use may play a key role in shaping the mosquito community within urban mangroves through either species spillover or altering the abundance of mosquitoes associated with the mangrove. In this study, we explore the impact of land use within 500 m of urban mangroves on the abundance and diversity of adult mosquito populations. Carbon dioxide baited traps were used to sample host-seeking female mosquitoes around nine mangrove forest sites along the Parramatta River, Sydney, Australia. Specimens were identified to species and for each site, mosquito species abundance, species richness and diversity were calculated and were analyzed in linear mixed effects models. We found that the percentage of residential land and bushland in the surrounding area had a negative effect on mosquito abundance and species richness. Conversely, the amount of mangrove had a significant positive effect on mosquito abundance, and the amount of industrial land had a significant positive effect on species richness. These results demonstrate the need for site-specific investigations of mosquito communities associated with specific habitat types and the importance of considering surrounding land use in moderating local mosquito communities. A greater understanding of local land use and its influence on mosquito habitats could add substantially to the predictive power of disease risk models and assist local authorities develop policies for urban development and wetland rehabilitation.

Dr Suzi Claflin completed her PhD at Cornell University exploring environmental factors driving the spread of an aphid-borne potato virus on small-scale farms. She is now a postdoctoral research fellow at the Menzies Institute for Medical Research in Hobart, TAS. In her spare time she runs her own blog, Direct Transmission, focusing on disease and other public health issues (check it out here). To learn more about her doctoral research, follow this link!


Do outbreaks of mosquito-borne disease always follow floods?


Water, water everywhere…and mosquitoes soon to follow. It makes sense that with more water you’ll get more mosquitoes and with more mosquitoes you’ll get more mosquito-borne disease. Right? Well, not always.

With floods hitting parts of inland NSW, health authorities have issued warnings about mosquitoes and mosquito-borne disease.

Western NSW, has been substantially impacted by flooding this month and the region has been declared a natural disaster zone. The Lachlan River at Forbes has reached a level not seen for 25 years. There is a lot of water about. 35,000 mega litres of water has also been released from Wyangala dam resulting in further flooding. There could be more to come as “Superstorm 2016” continues to bring rain to south-east Australia. Evacuations continue.

The flooding has come at a time when the weather in warming up and there are already reports of mosquito numbers increasing. The biggest concern is that once the flood water recede, how long will pools of water remain, have mosquitoes got a “jump start”on the season?

On the other side of the world, Hurricane Matthew is threatening Florida. The Bahamas and Haiti have already been hit and more than 2 million people in the US have been told to evacuate their homes. Flooding is expected.


Mosquitoes need water

There is no doubt that mosquito populations can increase rapidly following flood. There is even a group of mosquitoes commonly called “floodwater mosquitoes“. The desiccation resistant eggs of these mosquitoes are laying dormant in the cracks and crevices of flood plains, just waiting for the water to arrive. When it floods, the eggs hatch and in about a week or so, swarms of mosquitoes emerge.

For the most part, it isn’t immediately following the flooding, but in the weeks and even months following that can provide the most ideal conditions for mosquitoes. If temperatures aren’t high enough to drive rapid evaporation of ponding (or if additional rainfall keeps them topped up), mosquitoes can start building impressing population abundances. With more mosquitoes, the risk of mosquito-borne disease outbreak can increase.


Rainfall records provided by the Bureau of Meteorology indicate that over the three months to September 2016, some regions of NT, QLD, NSW and Victoria received some of their highest rainfall on record for the period. (Bureau of Meterology)

A look back to floods and mosquito surveillance

In 2011-2012, QLD, NSW and Victoria saw incredible flooding. For those of us working in the field of mosquito-borne disease, we’re well aware of what that flooding can cause. Our attention was sparked when stories starting coming out from locals about this being the biggest flooding since the 1970s. Why was this important? Following flooding in the 1970s, we saw one of the biggest outbreaks of the potentially fatal Murray Valley encephalitis virus Australia has seen. This outbreak, and the response to the actual and potential health impacts, was essentially the genesis of many mosquito-borne disease surveillance programs across the country.

One of those programs was the NSW Arbovirus Surveillance and Mosquito Monitoring Program. Following the flooding in early 2012, there was a huge jump in mosquito populations in western NSW and one of the largest collections of mosquitoes in the history of the program was recorded with over 18,000 mosquitoes collected! Fortunately, we didn’t see any substantial activity of Muray Valley encephalitis virus but elsewhere in Australia, cases were reported.


Mosquito-borne disease outbreaks need more than just mosquitoes

There is little doubt you need mosquitoes about for pathogen transmission. However, for many mosquito-borne diseases, the pathogens that cause the illness in people are naturally found in wildlife. Person to person transmission may occur but for pathogens such as West Nile virus, Ross River virus or Murray Valley encephalitis virus, the mosquitoes that inject their virus-filled saliva into people have bitten birds or mammals previously.

The role of wildlife is important to consider as the flooding may influence mosquito populations but they can also influence wildlife. While kangaroos and wallabies may be adversely impacted by floods, flood waters can provide a major boost for waterbirds.

In some instances, as is the case for Murray Valley encephalitis virus, floods provide ideal conditions for both mosquitoes and birds!


Do floods really cause outbreaks of mosquito-borne disease?

There are few studies that have demonstrated that outbreaks of mosquito-borne disease always occur following floods.

Studies in North America had previously concluded that there wasn’t a direct link between hurricanes and flooding and mosquito-borne disease. But, that doesn’t mean there won’t potentially be a boost in nuisance-biting mosquitoes following flooding.There is often widespread spraying to control these pest mosquito populations.

Interestingly, after Hurricane Katrina hit New Orleans in 2005, there was an increase in mosquito-borne disease with more than a 2-fold increase in West Nile neuroinvasive disease. However, other reports noted no significant increase in cases of either West Nile or St. Louis encephalitis viruses. Surveillance for 6 weeks following the hurricane, authorities found no arboviruses circulating in local mosquito populations. These results highlight that much more than water and mosquitoes are required for outbreaks of disease.

In Australia, a recent review looked at the influence of flooding on cases of Ross River virus disease. They found that the evidence to support a positive association between flooding and RRV outbreaks is largely circumstantial. The trouble in predicting outbreaks of Ross River virus disease is that there can be complex biological, environmental and climatic drivers at work and, irrespective of local flooding, there may be other region-specific issues that either increase or decrease the potential for an outbreak.

What should we expect in Australia as summer approaches?

There is no doubt mosquito repellent will come in handy over the coming months. There are already reports of increased mosquito populations in some parts of the country. While nuisance-biting impacts will be a worry, if mosquito populations further increase following flooding, authorities need to remain mindful of a range of other health risks too.

The good news is that unless higher than normal mosquito populations persist into the warmer months, we may not see major outbreaks of disease. It typically isn’t until November-December that we start to see pathogens circulate more widely among wildlife and mosquitoes. Hopefully, if some hot weather arrives, the flood waters will quickly evaporate and abundant mosquitoes populations won’t continue.

Current outlooks suggest that between now and December 2016, south-eastern regions of Australia are likely to receive above average rainfall. Temperatures, though, are likely to be a little cooler than normal. We’re probably lucky that this cooler weather will keep the really big mosquito population increases that we saw a few years ago at bay.

On balance, we’re expecting plenty of mosquitoes to be about as summer starts, hopefully not “mozziegeddon” but enough to ensure the community should stay aware of the health risks associated with mosquito bites and how best to avoid their bites.

Have you seen mosquitoes about already this season? Join the conversation and tweet some shots of local mosquitoes!