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.

 

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Talking wetlands, wildlife and mosquitoes at the 2017 Australian Entomological Society Meeting

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I’ll be in Terrigal, on the NSW Central Coast, for the 2017 Australian Entomological Society conference and taking the opportunity to present a summary of a number of collaborative projects undertaken in recent years, from working out how surrounding landuse influences the mosquito populations in urban mangroves to how important mosquitoes are to the diet of local bats.

Together with a range of colleagues, I’ve been undertaking research into the factors driving mosquito and mosquito-borne disease risk in urban wetlands. It is a complex puzzle to solve with more than just mosquitoes determining local pest and public health risks. However, with outbreaks of mosquito-borne Ross River virus on the rise in recent years, including urban areas of Australia, there is a need to better understand the factors at play.

There is a range of factors that may increase the risk of Ross River virus, they include suitable wetlands, wildlife reservoirs of the pathogen and mosquitoes. Understanding the mosquitoes associated with urban estuarine and freshwater wetlands is critical.

Investigating the role of surrounding landuse in determining the mosquito communities of urban mangroves, we found that industrial and residential areas tended to increase abundance of mosquitoes, perhaps due to direct or indirect impacts on the health of those mangroves. We’ve found previously that mosquitoes problems are often associated with estuarine wetlands suffering poor health, perhaps this is determining the increased mosquito risk we identified? You can read more in our publication here.

Expanding the investigation to look at urban freshwater wetlands, it was found that there was a high degree of variability in local mosquito populations and that each wetland needed to be assessed with consideration to be given to site-specific characteristics. You can read more about our work investigating mosquito assemblages associated with urban water bodies in our publication here.

More research is underway in this field and my PhD student, Jayne Hanford, has already started collecting some fascinating data on wetland biodiversity and local mosquito populations.

While the focus of our studies is often prompted by concern about Ross River virus, interestingly, in recent years we’ve found considerable activity of Stratford virus. This is not currently considered a major human health concern but given how widespread it is, it raises concerns about the suitability of local wildlife, even in Western Sydney, to represent important reservoirs of mosquito-borne pathogens. You can read more about Stratford virus in our publication here.

The final piece of the puzzle is to understand the ecological role of mosquitoes. Where their potential health threats are deemed significant, how could management of mosquito populations have unintended consequences for other wildlife. What about the animals that eat mosquitoes? A number of years ago we did some research to determine the importance of mosquitoes in the diet of coastal bats. While there was no indication that mosquitoes are a critical component of their diet, they are still being snacked on and mosquito control programs need to consider any local ecological impacts.

Now, how am I going to squeeze all this into 15 minutes….

The presentation abstract is below:

What drives mosquito-borne disease risk in urban wetlands?

Webb, C. (1, 2), J. Hanford (3), S. Claflin (4), W. Crocker (5), K. Maute (5), K. French (5), L. Gonsalves (6) & D. Hochuli (3)

(1) Department of Medical Entomology, NSW Health Pathology, Westmead Hospital, NSW 2145; (2) Marie Bashir Institute of Infectious Diseases and Biosecurity, University of Sydney, Camperdown, NSW 2006; (3) School of Life and Environmental Sciences, Faculty of Science, The University of Sydney, Camperdown, NSW, 2006; (4) Menzies Institute for Medical Research, University of Tasmania, Hobart, TAS, 7000; (5) Centre for Sustainable Ecosystem Solutions, Biological Sciences, Faculty of Science, Medicine & Health, University of Wollongong NSW, 2522; (6) School of Arts and Sciences, Australian Catholic University, North Sydney, NSW, 2060.

Managing pest and public health risks associated with constructed and rehabilitated urban wetlands is of increasing concern for local authorities. While strategic conservation of wetlands and wildlife is required to mitigate the impacts of urbanisation and climate change, concomitant increases in mosquitoes and mosquito-borne disease outbreak risk must be addressed. However, with gaps in our understanding of the ecological role of mosquitoes, could control strategies have unintended adverse impacts on vertebrate and invertebrate communities? A series of studies were undertaken in urban wetlands of greater Sydney to investigate the role of land use, wetland type and wetland aquatic biodiversity in driving the abundance and diversity of mosquito populations. A diverse range of mosquitoes, including key pest an vector species, were found in urban environments and mosquito-borne pathogens were detected in local populations, implicating local wildlife (e.g. water birds and macropods) as potential public health risk factors. Estuarine wetlands are locally important with the percentage of residential land and bushland surrounding wetlands having a negative effect on mosquito abundance and species richness while the amount of industrial land had a significant positive effect on species richness. Mosquito control in these habitats is required but insectivorous bats were identified as mosquito predators and the indirect implications of mosquito control should be considered. The aquatic biodiversity of urban freshwater wetlands influenced the species richness of local mosquito populations indicating vegetation plays an important role in determining local pest species. However, the matrix of wetland types also influences the abundance of mosquitoes in the local area. These results demonstrate the need for site-specific investigations of mosquito communities to assist local authorities develop policies for urban development and wetland rehabilitation that balance the need for conservation with reduced public health risks.

To keep up to date on what’s happening at the conference, check out the program online or follow the conversation on Twitter.

 

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.

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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!

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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.

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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:

repellents_potterpaper

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.

Moving pictures and managing mosquitoes

Mangroves_Video_June2016

For a few months now I’ve been thinking through some future options for the blog and my science communications activities. I’ve been toying around with starting a podcast or video blog about my work in local wetlands.

#MosquitoWeek has just happened in the U.S. and as it coincided with the close of entries with the Entomological Society of America YouTube competition, I thought what better time to play around with putting together a video.

A year or so ago I had the chance to see Karen McKee (aka The Scientist Videographer) talk about social media and the ways she uses video as a critical component of her community engagement and communications. Since I’m already using Instagram to connect followers with my various wetland sites and mosquito studies (as well as other things), I’ve thought video could be a way to go.

Interesting too since images and video are (or are soon to be) increasingly dominant in social media.

I’m an advocate for mosquito control to be part of overall wetland management. I think I’m sometimes seen as the enemy of wetland and wildlife conservation, not surprising given the perception of mosquito control still influenced by the DDT debate. As we push for the construction and rehabilitation of urban wetlands, the pest and public health risks associated with mosquito populations do need to be considered by local authorities.

I’m often arguing that ecologically sustainable mosquito management is actually critical to wetland conservation. If you’re encouraging the community to visit your wetlands, what happens when they’re chased away by mosquitoes? What about the community living around the wetland? Will nuisance-biting erode the good will of the community for wetland conservation?

You can watch my video, “Why is mosquito management important in our local wetlands?”, at YouTube or below:

You can check out some of my other posts of wetlands, mosquitoes and social media below:

Should we start pulling out mangroves to save our wetlands?

Does wetland rehabilitation need mosquito control?

Can social media help track environmental change?

Mosquitoes, constructed wetlands, urban design and climate change: Some workshop resources

Let me know if you’d be interested in seeing more videos! Send me a tweet.

Should we start pulling out mangroves to save our wetlands?

mangroves_webb_SOPA_November2015

You have no idea how badly I wanted to jump down into the thick black mud.

I don’t remember much about primary school but I do have strong recollections of an assignment on the importance of mangroves to the ecology of the Parramatta River. Perhaps not the assignment itself, but I do remember Mum and Dad taking me down to the river and I drew some pictures of the twists and turns of branches and trunks and the finger-like pneumatophores punching up through the thick dark grey mud. It may only have been 10 minutes drive from home in Western Sydney but it was a glimpse into a world so strange and alluring, how could it not have made an impact on me?

I remember the great disappointment of my parent’s stern words keeping me from jumping down below the high water mark and into the mud. The same feelings of frustration and disappointment when stopped from doing other fun things like playing in stormwater drains, letting off firecrackers or swimming in rips!

Mangroves don’t just attract the attention of young environmental scientists. Exploiting a unique place between the land and sea, mangroves have intrigued and fascinated many before me with the first descriptions, by Greek mariners, thought to date back to 325BC. What were these plants that seemed to defy logic, growing half submerged in salty water?

Almost thirty years after my primary school assignment, with sandshoes replaced by gumboots, that childhood disappointment of adventure squashed is now matched by the realisation that mangroves aren’t perfect. In fact, they’re a threat to some of the other plants and animals found in our local local estuaries.

Now I spend most of my summer coated in that same dark grey mud, covered in mosquito bites and thinking about how important mangrove management will be for the future of our coastal wetlands.

mangroves_duckcreek

More than mangroves

There is little doubt mangroves are an ecologically important habitat. They provide a home for a wide range of creatures, from bacteria to birds. Rich in nutrients and hiding places, mangroves are perfect nurseries for fish and crustaceans. Bird and bats and rodents and reptiles all find a home here too.

They’re threatened by climate change but they may also play a critical role in protecting our shoreline against sea level rise and storm surges. Sea level rise itself may knock out mangrove forests too but mangroves could also mitigate the impacts of climate change by storing carbon. In fact, the role estuarine wetlands may play in keeping carbon dioxide out of the atmosphere could be critical.

Make no mistake, mangroves are important. Thing is, it is also important to also remember that estuarine wetlands are more than just mangroves.

When we talk about estuarine wetlands, we’re grouping together a number of habitats that  include seagrass, saltmarsh, sedgelands and mudflats as well as mangroves. Each of these habitats play an important role in the functioning of the estuary as a whole but they each, individually, provide something specific to the wildlife that utilise the wetlands.

darkmangroves

Saltmarshes are critically important and are in desperate need of conservation. In NSW they’re listed as Endangered Ecological Communities. As well as urbanisation and pollution, a changing climate and sea level rise risk severely degrading the quality of these habitats.

One of the key threats facing saltmarshes is a native plant. A native estuarine wetland plant. Mangroves.

The encroachment of mangroves into saltmashes is a serious problem. This is happening in many parts of the world. It is a strange situation in which one native plant is taking over another and with these ecological shifts, there are knock-on effects to other components of the wetland ecosystem. Most importantly, nesting and feeding shorebirds.

saltmarsh_SOPA

Are mangroves really a threat?

The mangroves are just doing what mangroves do. The reason they’re threatening saltmarshes is due to our modification of local environments.

Urban runoff reduces the salinity of these wetlands and this reduced salinity not only removes the ecological advantages of salt-tolerent saltmarsh plants, such as Sarcocornia quinqueflora and Sporobolus virginicus, but it helps mangrove seeds and seedlings survive the otherwise harsh environmental conditions of saltmarshes. Lower the salinity, increase the invasive potential of mangroves.

Frequent dryness and highly salty conditions are a saltmarsh’s best defense against invading mangroves.

Filling in wetlands and the construction of seawalls, roadways and other infrastructure give saltmarshes little refuge or respite from these threats. While mangroves encroach from the sea, there is nowhere for saltmarshes to migrate to when dealing with sea level rise.

They’re cornered and under attack but even where the plants are persisting, the quality of habitat they provide for local wildlife is slowly degraded by colonising mangrove seedlings.

Blackwingedstilt_henandchickenbay_1september2015

There are many waterbirds that use our local estuaries that are under threat. Saltmarshes are great habitats for migratory shorebirds. There are plentiful resources in the form of insects and other invertebrates within the sediments. The birds can nest on the marsh and as they can see all around, predators are easy to spot. They feel safe.

There have been declines in the White-fronted Chat populations around Sydney. Many other populations of wading birds associated with Australia’s coastal wetlands are in decline too. Mangrove invasion isn’t the only thing to blame but it is an issue that needs to be addressed.

For many of these birds, the encroachment of mangroves into mudflats and saltmarshes is a problem. Its a problem for their foraging and nesting. Once mangrove seedlings start popping up on the middle of the saltmarsh, all those advantages of a wide open habitat in which predators are easy to spot are lost.

Imagine you’re a black-winged stilt. You’re trying to find a safe place to nest. A perfect place would be a raised area of saltmarsh surrounded by water. A dead flat saltmarsh with clear lines of sight for dozens of meters around. You’ll be able to see an approaching predator (like a fox or a feral cat) from far enough way to escape with plenty of time to spare. Now, stick a few mangrove seedlings here and there. They start to obscure your view. They’ll give sneaky predators a place to hide. Even if there are not predators about, you’ll probably get nervous. You’ll probably spend more time thinking about the threat of predators and less time foraging for food.

As mangroves move in, the birds will leave. Long before the saltmarsh is over run by mangroves, out-competed by the shade of establishing young mangroves, the quality of the habitat for many shorebirds will have already been lost. There may be some plants remaining but the ecological role of the habitat is gone.

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Do historic paintings provide conflicting evidence to the commonly held view that mangroves have always been present along the Parramatta River? (Parramatta River, c. 1837, Conrad Martens (1801-78) via Australian Art Auctions)

Painting the picture of change in the local wetlands

How can we predict what will happen in the future if we haven’t learned from the past?

Tracking change in these wetlands is important. The use of photography has played an important role in tracking environmental change for a long time. Aerial photography and satellite imagery have helped reveal dramatic changes in vegetation associated with Australia’s coastal wetlands. This analysis has demonstrated the encroachment of mangroves into saltmarshes and this encroachment is considered a key threatening process of this endangered ecological community.

How can we track the encroachment of mangroves? While technology has helped reveal current changes in mangrove encroachment, other uses of imagery can explore relatively recent “urban myths” about historic mangrove distribution.

Thinking back to that school assignment, I remember being told how important mangroves were to the local environment. We we taught that, here in Sydney, that mangroves were always part of the Parramatta River estuary, that they have alwasy been a critical component of the river’s ecology. Was this really the case?

There has been some brilliant detective work done to determine the historic distribution of mangroves along the Parramatta River in this paper titled “Estuarine wetlands distribution along the Parramatta River, Sydney, 1788–1940: implications for planning and conservation“. The authors have used old photos and, in particular, some of the earliest paintings from the Sydney region (together with notes from settlers at the time) and found that the estuary was dominated by mudflats and saltmarsh habitats and that extensive areas of mangroves did not occur until the 20th Century.

To quote the author, Lynette C. McLoughlin:

“These historical sources indicate that in the 19th century extensive mudflats and saltmarsh communities dominated the inter-tidal zone, with mangroves more limited to creek fringes and some patches in bays for much of the period. In the upper river from Subiaco Creek to Parramatta, there is no evidence for the presence of mangroves until the 1870s. Following settlement and increased sedimentation, inter-tidal mudflats expanded, mangroves colonised up river and out onto mudflats in bays in the latter part of the 19th century, followed by expansion into saltmarsh in the 20th century.”

It is only relatively recently that mangroves have really flourished along the river.

There is absolutely no doubt they were always present, tucked away in the tiny bays and inlets of what became known as Sydney Harbour but it was the mudflats and saltmarshes that dominated much of the estuary. These habitats, no doubt, provided a rich and productive habitat for shorebirds and other wildlife.

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So, where to from here?

Globally, mangroves are a critical component of wetland ecosystems. There is little doubt of that, and little doubt that in many parts of the world, even here in Australia, they are under threat. But so is saltmarsh and, saltmarsh is far less likely to be given the chance to demonstrate the resilience that mangroves will to continued changed environmental conditions results from a rising sea level and surging urbanisation.

Not just saltmarsh but mudlfats too.

Coastal authorities are increasingly aware of the need to balance protection of mangrove forests and the benefits they provide but also the conservation of saltmarsh and mudflats that are so critical to shorebirds.

The reality is, there will need to be a program of mangrove culling to sustain conservation of saltmarsh habitat. You need a permit to remove mangrove seedlings but a seasonal program of removal would be greatly beneficial in stopped the spread of mangroves into saltmarsh habitats. Local authorities are incorporating mangrove removal programs in their local wetland rehabilitation programs.

Removing young seedlings is easy, you can pull them straight out of the wet mud. Wouldn’t take much to organise a team of volunteers to move through the local saltmarsh removing seedlings. Perhaps in Autumn when the migratory shorebirds have left and the mosquito populations aren’t so bad?

The idea that native vegetation should be actively removed from habitats sounds at odds with environmental conservation. However, we need to maintain our wetlands for our future generations and the next generations of birds, and fish and crustaceans that rely on them now where few other opportunities exist.

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2 February is World Wetlands Day. Please get out into your local wetlands, or at least make a pledge to visit your nearby wetlands sometime soon.

Learn more about Australia’s amazing mangroves by dropping by MangroveWatch and picking up the excellent Australia’s Mangroves by Norm Duke. There is also an extremely useful text on Australian Saltmarshes that is essential.

Finally, check out one of the most extensive resources on urban wetland management, including estuarine wetlands, via the free eBook produced by the Sydney Olympic Park Authority titled “Workbook for Managing Urban Wetlands in Australia“. Read a brief article on our analysis of the use of this resource in the latest issue of Wetlands Australia, see “Insights from the use of an online wetland management resource” by Webb and Paul (pages 26-27).

What are you doing for World Wetlands Day? Join the conversation on Twitter!

Want to learn more about the amazing world of Australian mosquitoes? Check out “A Field Guide to Mosquitoes of Australia” out now through CSIRO Publishing. Over 200 pages containing a pictorial guide to almost 100 different mosquitoes along with tips on beating their bite and protecting your family from the health risks of mosquitoes. You can order online or through your favourite local bookstore or online retailer.

 

How to beat the bite of backyard mosquitoes

dude_sandpit_30032014Summer is here and you’ll want to know how to spend time in the backyard without a barrage of bites from pesky mosquitoes!

There is little doubt mosquitoes are a nuisance but in some parts of Australia but they can also pose a health risk. Around 5,000 people a year are infected with Ross River virus. In fact, 2015 saw the biggest outbreak of mosquito-borne Ross River virus disease ever recorded in Australia.

I recently shared ten tips on keeping free of mosquito bites with the University of Sydney that proved popular so now here are five top tips (with a bit more detail) to help reduce the risk of mosquito bites and get the most out of your backyard this summer!

Water water everywhere, just what mozzies love

Don’t let mosquitoes find a home around your home.

The immature stages of mosquitoes (commonly known as wrigglers) are found in free-standing water so drain, tip out or cover any water holding containers. These can range from buckets and discarded tyres to children’s toys and slumped tarpaulins covering boats or trailers.

Flush out your bird baths with a hose once a week (you can also scrub it with wire brush to dislodge any mosquito eggs). Mosquitoes can even find a home in your pet’s water bowl so empty before refilling at least once a week.

Can you see a puddle or pool of water? There are probably mosquitoes in there, or dozens of eggs waiting to hatch.

Pot plant saucers (particularly “self watering” pots) are great places for mosquitoes. If you fill saucers with sand, the moisture will be trapped but there won’t be any “free standing” water for mosquitoes to use. Good for the plants, bad for mosquitoes.

Sometimes the problem comes from above. Check your roof gutters, when they get blocked with leaves and water is trapped it provides habitat for mosquitoes. Same goes for courtyard drains, make sure you clean out soil, sand and other debris that might trap pools of water.

Make sure you keep your swimming pool chlorinated. Neglected swimming pools can harbour mosquitoes, especially mostly empty in-ground pools that partially fill following rainfall.

Webb_bucketsofrainwater

It may seem like a good idea to store water around the home to help keep plants going during a long hot summer but any water, from a full rainwater tank to a few drops in the base of a pot plant saucer, can make a great home for mosquitoes!

Spray with care (if you really need to)

A range of products is available that will help control mosquitoes. It is important to ensure that any product used is registered with the Australian Pesticides and Veterinary Medicines Authority (APVMA). The APVMA test products for their effectiveness and safety and it is critical that the instructions on the insecticide label are followed.

The insect growth regulator methoprene (NoMoz) and the monomolecular film (Aquatain) can both be used to stop mosquitoes emerging from backyard habitats. A few pellets of methoprene or a few drops of monomolecular film into water can be enough to provide a month or so of mosquito control. It was once common practice to put a teaspoon of kerosene into rainwater tanks (the kerosene floats on the surface of the water, drowning mosquito wrigglers), now monomolecular films can be used. Keep in mind though, if your rainwater tank is properly screened, you don’t need to worry about putting anything inside.

For mosquitoes flying in from beyond the backyard, sometimes you need to use insecticides. Insecticide sprays generally fall into one of two categories. “Knockdown” sprays are designed to kill flying insects while they’re buzzing about. While they’ll certainly kill mosquitoes, mosquitoes are far less likely to be randomly flying about in the backyard. They’re usually a little more sneaky than that. A better option will be “surface sprays” that provide some residual control and kill the mozzies where they hide out.

Residual insecticides (typically containing synthetic pyrethroids and often marketed as “surface sprays”) can be applied to cool and shaded areas. The most effective places will be under outdoor furniture, the shaded sides of buildings, verandas or within vegetation. While these products are safe for people and pets, they are likely to impact non-target insects too (e.g. bees, butterflies, beetles) so should be employed judiciously, especially if spraying on plants. Never spray them into or around ponds as these insecticides can be toxic to fish. Always check the label of the insecticide for directions.

I once asked a local resident if this type of spraying worked in reducing mosquito numbers around the home. “Yeah, it killed everything” they replied. We really don’t want to be killing everything so please be careful when using these products.

vintage_bugspray_

Vintage insecticide advertising (Source: Envisioning the American Dream)

Topical mosquito repellents will remain the first line of defence for many when mosquitoes are out in force. Products that contain DEET (diethyltoluamide) or picaridin will provide the longest lasting protection but make sure they’re applied correctly. You’ll need a thin coverage of all exposed skin. A dab “here and there” won’t be enough. Plant-based products (e.g. tee tree oil) will provide some protection but will generally need to be applied more frequently than the other repellents to ensure long lasting mosquito bite protection.

Burning coils and switching on zappers

The smell of mosquito coils is up there with the smell of sunscreen and BBQs as a reminder of summer. Mosquito coils and sticks are good at reducing the number of mosquito bites but they’re unlikely to stop them all. A recent study found little evidence that burning mosquito coils prevents malaria so don’t expect all biting mosquitoes to stop once you light up a coil. Make sure you use coils or sticks that contain insecticide (e.g. pyrethroid) and not just botanical extracts (e.g. citronella) as the insecticides will actually kill some mosquitoes.

Never sleep in an enclosed room with a mosquito coil burning. Seriously, don’t keep a mosquito coil burning overnight in your bedroom.

There is a range of “smokeless” ways to beat mosquitoes too. These are either plug-in or butane powered units that heat insecticide impregnated pads, or reservoirs of liquid. Most of these types of units are designed for indoor use but they’ll work just as well in sheltered balconies or courtyards too. Like the insecticide impregnated coils and sticks, these products provide the best bite protection but without the smoke.

You can also forget about the various types of mosquito traps on the market. Some may catch mosquitoes but never enough to stop bites in the backyard. Electrocuting traps and those with UV lights are generally ineffective at catching mosquitoes, you’ll catch many more non-biting flies, moths and beetle than mosquitoes.

birdhouse

Encourage the creatures that will eat mosquitoes

Mosquitoes are food for fish, frogs, birds and bats. Can they help keep mosquito numbers down?

Fish eat mosquito wrigglers so release some (native fish preferably) into your ornamental ponds. Best not release “mosquitofish” (aka the plague minnow, Gambusia holbrooki) as these will chomp through more than just mozzies (say good bye to native fish and tadpoles!). Contact your local council who can provide some advice on what fish may be best suited to your local area. If you’ve got frogs about, tadpoles won’t munch through many wrigglers, but having frogs about is reward enough anyway!

Many claim that encouraging birds or bats to move in around the house will help reduce mosquitoes. A garden of native shrubs and ground covers will provide a home for small insect-eating birds so at least some local animals will be snacking on mozzies. But don’t buy bird houses and bat boxes expecting all the bites to disappear. Although birds and bats do eat mosquitoes, they don’t eat anywhere near enough to reduce nuisance biting. Encourage these creatures because they’re nice to have around, not because they’ll provide pest control.

There are some mosquitoes whose wrigglers will actually eat the wrigglers of other mosquitoes. The news gets even better because these mosquitoes (Toxorhynchites speciosus) don’t even bite (they’re also film stars)! Unfortunately, there will never be enough of them to eat enough mosquitoes to make a difference having them around (as well as other mosquito eating arthropods such as dragonflies, spiders, beetles and damselflies) can only help, even if it is just a little bit.

mosquitorepellentplants

Mosquito repellent plants aren’t repellent

Sounds like a dream that you could plant something in the garden that would “naturally” keep mosquitoes away. Problem is, none of the plants promoted as “mosquito repelling” provide any substantial protection.

Experiments in Africa found that some potted plants repelled around 30-40% of the mosquitoes. I’m somewhat sceptical of that success. Whenever I’ve tested spatial repellents, especially those containing plant extracts that are actively released in one way or another, I rarely get that success. Whole plants? I’m not so sure.

If you check out your local nursery, you may find a plant called “Mozzie Blocker” for sale. This plant is the Lemon Scented Gum (Leptospermum liversidgei). While the extracts from these types of trees (Leptospermum and Melaleuca species) have been shown to repel some mosquitoes, there is no evidence that the whole plant will reduce mosquito bites. It is worth remembering that these plants populate coastal swamp forests and I know from experience that these are some of the most intense places for biting mosquitoes you can find!

In summary, the nuisance caused by local mosquitoes will often be determined by the environment around your home as much as those in it but there are still things you can do to reduce their bites. Most important of all is ensuring you’re not creating opportunities for mosquitoes to breed and hang out in your backyard!

What’s your favourite way to beat the bite of backyard mosquitoes? Join the conversation in Twitter!

Want to learn more about the amazing world of Australian mosquitoes? Check out “A Field Guide to Mosquitoes of Australia” out now through CSIRO Publishing. Over 200 pages containing a pictorial guide to almost 100 different mosquitoes along with tips on beating their bite and protecting your family from the health risks of mosquitoes. You can order online or through your favourite local bookstore or online retailer.

 

 

 

 

Asian tigers and shifting mosquito control from the swamps to the suburbs

aedes_albopictus_SteveDoggettOne of the world’s most troublesome nuisance-biting mosquitoes is perfectly adapted to summer life in southern cities in Australia. This is bad news for communities in temperate climate regions in Australia that would otherwise be immune from the threats of exotic mosquito vectors of dengue and chikungunya virus otherwise limited to tropical regions of the world.

I’ve been invited to speak in the “Managing Current & Future Exotic Mosquito Threats” symposium at the Australian Entomological Society conference to share some of the experiences in temperate Australia regarding exotic and endemic mosquito threats and how the threat of the Asian Tiger Mosquito is being addressed.

Australia has annual activity of mosquito-borne disease. Around 5,000 people a year fall ill following a mosquito bite each year in Australia, most commonly due to Ross River virus. These pathogens are generally spread by native “wetland” mosquitoes such as Aedes vigilax or Culex annulirositrs). Australia has also had major outbreaks of dengue in the past but the only mosquito in Australia able to spread the viruses, Aedes aegypti, is restricted to far north QLD. It is unlikely to spread to southern cities beyond Brisbane based on temperature change alone but there is another mosquito that may pose a threat of dengue or chikungunya virus transmission in southern regions.

The Asian Tiger Mosquito (Aedes albopictus), poses a significant threat to Australia. It was discovered in the Torres Strait in 2005, having thought to have hitchhiked on fishing boats from Indonesia. Although the mosquito hasn’t yet managed to set up home on mainland Australia, its a more likely a question of when, not if, this mosquito will make its way here.

The container-inhabiting (not wetland living) mosquito has already hitchhiked to Europe and North America with eggs carried with people and their belongings. Movement of people, not shifts in climate is the biggest risk. Should it reach one of our major southern cities, there is little doubt that mosquito could become a persistent summer pest and possible public health threat. The way we respond to water shortages in our cities, by increasing water storage around our homes, may set the scene for this mozzie to move in.

Once the mosquito is established in our cities, all we need are travellers to bring in the viruses. Travellers introduce dengue virus into Far North QLD every year. Last year Japan experienced its biggest outbreak of dengue in over 70 years thanks to a traveller introducing the virus to local mosquitoes in downtown Tokyo. This Tokyo outbreak of dengue has implications for local authorities in Australia.

In my presentation at the Australian Entomological Society conference, I’ll highlight some of the issues to consider when assessing the risks posed by exotic mosquitoes in New South Wales as well as outline some of the problems local authorities may have to face when dealing with these mosquitoes that differ from the current focus of mosquito and mosquito-borne disease surveillance and control strategies.

You can view my presentation slides and abstract below:

Developing a strategic response to exotic mosquito threats in NSW

Cameron E Webb (1,2), Jay Nicolson (3), Andrew van den Hurk (4) & Stephen L Doggett (1)

(1)Department of Medical Entomology, Pathology West – ICPMR Westmead, Level 3, ICPMR, Westmead Hospital, Westmead NSW 2145 Australia; (2) Marie Bashir Institute of Infectious Disease and Biosecurity, University of Sydney, NSW 2006, Australia; (3) School of Pathology and Laboratory Medicine, The University of Western Australia, Nedlands, WA 6009, Australia; (4) Virology, Public and Environmental Health, Forensic and Scientific Services, Department of Health, Queensland Government, Brisbane, QLD 4108, Australia.

Mosquito-borne disease management in Australia faces challenges on many fronts. Home growth threats posed by endemic mosquito-borne pathogens (e.g. Ross River virus (RRV)) may increase with a changing climate but exotic mosquitoes and pathogens are an emerging threat. In the absence of a national strategy to address these exotic threats, local authorities must develop regionally specific surveillance and response programs to identify and respond to exotic mosquito incursion. The Asian tiger mosquito, Aedes albopictus, poses the greatest risk to temperate regions of Australia due to their close ecological associations with urban habitats and ability to transmit exotic pathogens (e.g. dengue viruses (DENV) and chikungunya virus (CHIKV)). The mosquito is widespread in local regions, has been detected at international ports and, given the increasing frequency of local travellers to regions where this mosquito is abundant, it raises the potential that an incursion into metropolitan Sydney in the coming years is probable. When this happens, what is the likelihood that this mosquito becomes established? Laboratory studies have confirmed Ae. albopictus could survive in the egg stage under climatic conditions typical of a Sydney winter. Despite the endemic mosquito, Aedes notoscriptus, sharing the same ecological niche to Ae. albopictus, cohabitation studies demonstrated that no interspecies competition would act to limit the local spread of Ae. albopictus and the mosquito could proliferating in the summer. Critically, vector competence experiments have demonstrated the ability of Ae. albopictus to transmit endemic pathogens and, given their propensity to bite humans, could contribute to human-mosquito-human outbreaks of RRV in urban areas of NSW, complementing the enzootic vectors that currently limit transmission to the metropolitan fringe. Local authorities need to develop a multiagency strategic approach to surveillance concomitant with strategic response to reduce the pest and public health threats associated with exotic mosquitoes.

Make sure you check out the tweets from the Australian Entomological Society Annual Conference in Cairns, QLD, 27 September through 1 October 2015, by clicking on #AusEntoSoc15