La Niña will give us a wet summer. That’s great weather for mozzies

The return of the La Niña weather pattern will see a wetter spring and summer in many parts of Australia.

We know mosquitoes need water to complete their life cycle. So does this mean Australia can expect a bumper mozzie season? How about a rise in mosquito-borne disease?

While we’ve seen more mosquitoes during past La Niña events, and we may well see more mosquitoes this year, this doesn’t necessarily mean we’ll see more related disease.

This depends on a range of other factors, including local wildlife, essential to the life cycle of disease-transmitting mosquitoes.

What is La Niña?

La Niña is a phase of the El Niño-Southern Oscillation, a pattern of ocean and atmospheric circulations over the Pacific Ocean.

While El Niño is generally associated with hot and dry conditions, La Niña is the opposite. La Niña brings slightly cooler but wetter conditions to many parts of Australia. During this phase, northern and eastern Australia are particularly likely to have a wetter spring and summer.

Australia’s most recent significant La Niña events were in 2010-11 and 2011-12.

Why is wet weather important for mosquitoes?

Mosquitoes lay their eggs on or around stagnant or still water. This could be water in ponds, backyard plant containers, clogged gutters, floodplains or wetlands. Mosquito larvae (or “wrigglers”) hatch and spend the next week or so in the water before emerging as adults and buzzing off to look for blood.

If the water dries up, they die. But the more rain we get, the more opportunities for mosquitoes to multiply.

Mosquitoes are more than just a nuisance. When they bite, they can transmit viruses or bacteria into our blood to make us sick.

While Australia is free of major outbreaks of internationally significant diseases such as dengue or malaria, every year mosquitoes still cause debilitating diseases.

These include transmission of Ross River virus, Barmah Forest virus and the potentially fatal Murray Valley encephalitis virus.

What happens when we get more rain?

We’ve know for a long time floods provide plenty of water to boost the abundance of mosquitoes. With more mosquitoes about, there is a higher risk of mosquito-borne disease.

The amount of rainfall each summer is also a key predictor for seasonal outbreaks of mosquito-borne disease, especially Ross River virus.

Inland regions of Queensland, New South Wales and Victoria, especially within the Murray Darling Basin, are particularly prone to “boom and bust” cycles of mosquitoes and mosquito-borne disease.

In these regions, the El Niño-Southern Oscillation is thought to play an important role in driving the risks of mosquito-borne disease.

The hot and dry conditions of El Niño aren’t typically ideal for mosquitoes.

But historically, major outbreaks of mosquito-borne disease have been associated with extensive inland flooding. This flooding is typically associated with prevailing La Niña conditions.

For instance, outbreaks of Murray Valley encephalitis in the 1950s and 1970s had significant impacts on human health and occurred at a time of moderate-to-strong La Niña events.

Over the past decade, when La Niña has brought above average rainfall and flooding, there have also been outbreaks of mosquito-borne disease.

These have included: Victoria’s record breaking epidemic of Ross River virus in 2016-17 after extensive inland flooding; southeast Queensland’s outbreak of Ross River virus in 2014-15, partly attributed to an increase in mosquitoes associated with freshwater habitats after seasonal rainfall; and eastern Australia’s major outbreaks of mosquito-borne disease associated with extensive flooding during two record breaking La Niñas between 2010 and 2012. These included Murray Valley encaphalitis and mosquito-borne illness in horses caused by the closely related West Nile virus (Kunjin strain).

We can’t say for certain there will be more disease

History and our understanding of mosquito biology means that with the prospect of more rain, we should expect more mosquitoes. But even when there are floods, predicting outbreaks of mosquito-borne disease isn’t always simple.

This is because of the role wildlife plays in the transmission cycles of Ross River virus and Murray Valley encephalitis virus.

In these cases, mosquitoes don’t hatch out of the floodwaters carrying viruses, ready to bite humans. These mosquitoes first have to bite wildlife, which is where they pick up the virus. Then, they bite humans.

So how local animals, such as kangaroos, wallabies and water birds, respond to rainfall and flooding will play a role in determining the risk of mosquito-borne disease. In some cases, flooding of inland wetlands can see an explosion in local water bird populations.

How can we reduce the risks?

There isn’t much we can do to change the weather but we can take steps to reduce the impacts of mosquitoes.

Wearing insect repellent when outdoors will help reduce your chance of mosquito bites. But it’s also important to tip out, cover up, or throw away any water-holding containers in our backyard, at least once a week.

Local authorities in many parts of Australia also undertake surveillance of mosquitoes and mosquito-borne pathogens. This provides an early warning of the risk of mosquito-borne disease.

This article originally appeared at The Conversation on 5 October 2020.

School is out (but don’t let mosquitoes bite)

“School’s out forever
School’s out for summer
School’s out with fever
School’s out completely” Alice Cooper

The end of the school year for students completing high school is here. School is out so the partying can start! Lets hope fever isn’t part of the story too.

For many students, this means traveling overseas for “schoolies” celebrations. The health and wellbeing of students attending “schoolies” has been front of mind of many parents and local authorities. This isn’t surprising given the risk taking behaviours many engage in.

Health authorities are often warning about potential health risks. However, with many travelling overseas for end of school celebrations, a range of mosquito related health risks may be experienced. The steps taking to avoid mosquito bites at home need to be changed if travelling to regions of the world where different mosquitoes and more serious mosquito-borne pathogens are found.

Overseas travel brings different risks

The risks may be significantly greater if travelling overseas to tropical regions such as SE Asia and the Pacific. Bali is a particularly popular party destination and also one with a high risk of mosquito-borne disease, especially dengue.

There are other mosquito-borne diseases to be wary of. Fortunately, the steps taken to avoid dengue will also assist in preventing exposure to Zika or Chikungunya too. There are occasionally cases of Japanese encephalitis virus in Australian travellers but they are rare.

Some regions will have a risk of malaria too. If you’re traveling to one of those regions, best consult your local travel health professional.

One of the main differences Australian travellers will face when spending time in regions prone to dengue outbreaks is that the mosquitoes that spread the virus bite during the day. We’re familiar with the local warnings to avoid mosquitoes at dawn, dusk, and overnight here in Australia. The mosquito that drives dengue outbreaks is most commonly Aedes aegypti, a mosquito that bites during the day.

We’re also likely to reach for the mosquito repellent when mosquitoes are abundant, as they often are, during summer coastal holidays. Bu Aedes aegypti is generally not that abundant. Don’t wait to notice the mosquitoes biting before putting on repellent.

These mosquitoes are also most likely to be present around urban areas and villages. These mosquitoes aren’t found in wetlands, they like living in water-filled containers where people live. Don’t think that just because you aren’t visiting wetlands or rainforests that there won’t be a risk of mosquito-borne disease!

Here are three tips on protecting yourself against mosquito-borne disease if you’re travelling overseas for “schoolies” celebrations:

1. Protect yourself against day-biting mosquitoes. Apply a repellent before breakfast and apply it like sunscreen. An even cover of exposed skin is required. Don’t bother applying it to clothing or “spraying it around the room”, that won’t protect you from bites.

2. Take repellent with you. Australian repellents must be registered with the Australian Pesticides and Veterinary Medicines Authority who test for efficacy and safety. You may not be able to get a hold of similar products overseas. Use a repellent that contains either diethyltoluamide (aka DEET) or picaridin; these formulations are readily available in local supermarkets and pharmacies. Oil of Lemon Eucalyptus is useful too but these formulations are often difficult to find.

3. Even if you’re staying at an expensive resort, where mosquito control is probably in place, take insect repellent for those day trips to local villages or markets. These are places and times where you may be exposed to “dengue mosquitoes”.

Don’t forget to check out Smart Traveller before heading off to Bali…or anywhere else for that matter. They provide all the updates on health and security concerns.

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Photo at top of this post by Jed Villejo on Unsplash

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How does a mosquito researcher mark the passing of seasons?

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

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

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

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

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

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

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

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

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

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

Say goodbye to summer holidays

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

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

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

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

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

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

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

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

Bring on the cold (and report writing)

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

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

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

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The long hot summer of mosquito and media wrangling

“Webb’s a mosquito researcher with NSW Health Pathology, and while it may sound like potentially the worst job in the world to the rest of us, it’s important work.” – Ten Daily, 14 Jan 2019.

Every summer I’m required to juggle those pesky mosquitoes and help out with requests from media. Over the past 6 months or so I’ve responded to about 70 media requests and here is a round up of some fun highlights and other bits and pieces.

There was a wide range of media requests this summer, from morning TV through to talkback radio, podcasts and live interviews via Skype. There was once a time when the only acceptable way to do a radio interview was via landline connected phone. This summer I did interviews via mobile, Skype, and various  smartphone apps! Times are a changing.

A fun segment on Channel 7’s ‘Sunrise’ breakfast show on why mosquitoes bite some people more than others; always a challenge taking in a cage a live mosquitoes to the studio, especially travelling in via public transport!

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A hot and dry summer must mean less mosquitoes, right?

The outlook for the 2018-2019 “mosquito season” was for it to be fairly routine. The Bureau of Meteorology was predicting a hot and dry summer under the influence of El Nino. At the time I wrote a piece for The Conversation highlighting that just because it was dry, that didn’t mean we wouldn’t see plenty of mosquitoes.

In coastal regions of Australia, tidal flooding of local wetlands often offsets any impact due to lack of rainfall. Mosquitoes such as Aedes vigilax certainly respond well and there were some very high mosquito numbers recorded in early spring. Usually, the media interest in mosquitoes starts increasing once the politicians break for the summer, this year there was plenty of interest early on!

NSW Health also issued a media release to get the community thinking about the potential mosquito impacts ahead of the summer holiday period and asked me to be the spokesperson. These warnings often prompt a different range of media interest, usually news bulletins for radio. Unlike the traditional radio interviews in which you’re responding to the host’s questions, only “grabs” (short statements regarding the topic) are required. I’ve learned there is a fine art to being concise in these statements and it pays to give some thought to what you’ll say ahead of calling up the news desk!

Some of the media coverage in early summer was less about bites and more about why mosquitoes disturb your sleep! I spoke with Channel Ten about how you can beat these bedroom buzzers! Here are some tips on beating the buzz of mosquitoes in the bedroom.

These concerns about mosquitoes in the bedroom prompted questions about the suitability of mosquito coils as a person protection measures. I’d written about this issue before but there was also some media coverage at the Daily Telegraph and Sydney Morning Herald.

There was also a funny segment on The Project:

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Warm weather, warm blood, and hungry mosquitoes

As summer kicked in, I did a bunch of “pre-season” interviews about the outlook for the mosquito activity ahead. One of them was with the Sydney Morning Herald. There was also a piece in Illawarra Murcury on the mosquitoes around Newcastle. I even chatted with ABC Illawarra about the mosquitoes bringing in the new year along the NSW coast. I also chatted with the team at the Daily Mail. Also the Daily Telegraph.

Once summer really hit (and the mosquitoes really started biting following heavy rains), everyone’s mind turned to one of the most commonly asked questions….why do mosquitoes bite me more than my friends? You can check out my contribution to a story by ABC Science below:

The usual coverage of mosquito impacts during the Australia Day holiday also popped up. Will my diet influence the likelihood of being bitten? I spoke with Channel Ten. The University of Sydney media team also put out a piece on why what you eat or drink makes not difference when it comes to stopping mosquito bites. A story picked up and republished by ABC News.

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Combining fieldwork and media requests

“Ballina council is calling in an expert to hunt for some ladies – Medical Entomologist Dr Cameron Webb will visit the area next week in search of blood sucking girls.” – EchoNet Daily, Ballina

While undertaking some work for Ballina Shire Council on the NSW far north coast, I helped out managing a few media requests associated with local mosquito problems and the work of council. It was fun squeezing in some print, TV, radio, and social media activities between the work in the wetlands.

I also participated in a “Q and A” on the Ballina Shire Council Facebook page where residents could ask questions about how best to protect themselves from mosquitoes. See here.

Mosquito-borne disease in the city

The detection of Ross River virus in mosquitoes around Sydney sparked some additional interest from media (and anxiety from local community). Coverage in Sydney Morning Herald here.  It prompted me to write an article about what the actual health implications were of finding the pathogen in a heavily urbanised areas such as the Parramatta River compared to the more bushland dominated Georges River.

The issue of wildlife and their role in urban transmission cycles of Ross River virus is always a tricky one. How do you balance wildlife conservation and mitigation of health risks? Together will colleagues I wrote about this at The Conversation.

The media coverage of the Ross River virus detection provided an opportunity for NSW Health Pathology to share some insights into how we research local mosquitoes and the pathogens they’re carrying. See below for a short video from the mangroves along the Parramatta River.

Did you know we monitor mosquitoes around the state to provide public health advice to @NSWHealth? Here’s our mozzie guru @Mozziebites (Dr Cameron Webb) explaining how we do this important work! pic.twitter.com/zpCTs7p3DL

— NSW Health Pathology (@NSWHPathology) January 10, 2019

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Declining insects, increasing mosquitoes, and the need to spray our backyards

One of the other stories bubbling along during the last year or so were the reports of declining global insect populations. I first spoke to the media about this issue back in early 2018. I was quoted in a couple of other stories too, clearly there was a lot of interest in this issue. This story gained plenty of attention and I spoke with various radio and print media about this challenge were facing with potential insect declines and how we can measure them. I even wrote an article about whether mosquitoes may be in decline too!

I spoke about this issue, and more generally about mosquitoes on an episode of the Science on Top podcast too.

There has been suggestions that insecticides may be contributing to declining insect populations. Earlier in the year, I was one of the coauthors of a paper that called for the need to better understand integrated pest control in our cities and become less reliant on insecticides. There was also an associated article at The Conversation. This was also republished at Domain.

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Floods in the north, floods in the south

The incredible flooding around Townsville in far north QLD created some major concern. Despite some initial concerns about increased mosquito risk, there weren’t any substantial increases in mosquito-borne disease reported. I spoke to ABC News about the potential risks.

The flooding that did trigger a big boost in mosquito numbers occurred in SE QLD and northern NSW. Local wetlands were inundated by tides and rain, resulting in some phenomenal numbers of mosquitoes in early autumn. I spoke to ABC and Great Lakes Advocate about the climatic factors that triggered this unusual mosquito activity.

Everyone was on weather watch late in the season too. A few extra downpours prompted concerns about more increases in autumn mosquito populations. I spoke with Sydney Morning Herald after a particularly wet weekend in March.

Finally, I helped the Australian Academy of Science make a video exploring why mosquitoes bite and how to stop them!

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Join the conversation on Twitter, did you catch me talking mosquitoes this summer? Did it help you protect your family from mosquito bites?

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Could a boombox (playing Skrillex) save you from mosquito bites?

There has been quite a buzz about some new research that suggests the music playing at your next backyard party may keep the mosquitoes at bay. Could it actually be true?

“As music is loved by many people, the development of music-based anti-mosquito control measures may represent an appealing alternative to strategies involving the use of harmful chemical insecticides.” – Dieng et al. 2019

Are mosquitoes monsters or sprites?

The study was recently published in the peer-reviewed journal Acta Tropica. The researchers (including one of my previous PhD students) exposed mosquitoes to the song “Scary Monsters And Nice Sprites” by U.S. electronic dub-step artist Skrillex while recording how long it took Aedes aegypti (these are the mosquitoes that transmit dengue viruses) to find a blood meal, how long they spent feeding, as well as tracking how much time was spent mating. The “blood meal” was provided by a restrained hamster and all experiments were conducted in the laboratory.

“Adults entertained with music copulated far less than their counterparts kept in the environment where there was no music entertainment.” – Dieng et al. 2019

Unfortunately, the researchers didn’t explain why they decided to use this particular song, only describing it as “…characterized as noisy based on the resulting vibragram and strong sound pressure/vibration with constantly rising pitches”. It would have been interesting to include a couple of other songs in the testing too. Perhaps something a little more downbeat?

Once they had the song playing (ensuring the speakers weren’t located close enough to cause vibration to the cage containing mosquitoes), mosquitoes were released into the cage and behaviour was recorded for 10 minutes. Researchers recorded the time to first blood feeding attempt, number of blood feeding events, and number of mating events.

The results were interesting. Mosquitoes took longer to find a host, spent less time blood feeding and mated less often when exposed to the music. These differences in each measurement were statistically different too.

What does this mean for prevention of mosquito-borne disease?

This study has received plenty of media attention. See here and here and here. I spoke to ABC Sydney about it too (tune in from the 1:07).

While the results demonstrated some reduced likelihood of biting, it shouldn’t be interpreted that playing Skrillex’s music will protect yourself from mosquito bites. The reduced likelihood was pretty short lived, you’re pretty much guaranteed to get bitten despite the dub step blasting from the boombox.

There has always been an interest in understanding how sound impacts the behaviour of mosquitoes. Ultrasonic insect repellents have been sold in one way or another for a couple of decades. Now you can download apps to your smartphone that purport to use sound to repel mosquitoes. There really is no evidence that sound can provide protection from mosquito bites.

Digging deeper into the “Skrillex study”, the results indicate that even though there may be less chance you’ll be bitten while listening to this music, you’ll still be bitten. Even over the relatively short exposure periods in the laboratory study, the mosquitoes were still biting. Notwithstanding your tolerance of Skrillex’s brand of electronic music, who knows how loud you need to be playing it or how shifts in songs (and their associated pitches, frequencies, buzzes, and beats) may change the activity of local mosquitoes.

To prevent mosquito-borne disease, you need to stop all bites, not just some of them. Topical insect repellents will still provide better protection. Keep in mind that even a low dose DEET-based insect repellent will prevent all bites from Aedes aegypti for a few hours in laboratory testing.

See the full paper here:

Dieng, H., Chuin, T.C., Satho, T., Miake, F., Wydiamala, E., Kassim, N.F.A., Hashim, N.A., Vargas, R.E.M. and Morales, N.P., 2019. The electronic song “Scary Monsters and Nice Sprites” reduces host attack and mating success in the dengue vector Aedes aegypti. Acta Tropica. [online]

 

Join the conversation on Twitter, if music could keep mosquitoes away, what music would you want that to be?

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Photo at the top of this article by Eric Nopanen on Unsplash

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Why has mosquito-borne disease hit Tasmania?

Are there even mosquitoes in Tasmania?

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

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

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

Fortunately the disease is not fatal.

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

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

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

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

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

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

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

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

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Ross River virus in Sydney, should we be worried?

Health authorities in NSW recently released warnings to avoid mosquito bites following the detection of Ross River virus in wetlands along two major river systems in metropolitan Sydney. Whats going on and should these findings be something to be worried about?

What is Ross River virus?

Ross River virus is the most commonly reported mosquito-borne disease in Australia. The virus is spread by the bite of a mosquito and about 40 different mosquito species have been implicated in its transmission.

The disease caused by Ross River virus is not fatal but it can be severely debilitating.

Thousands of Australian’s are infected each year. We have some idea of the quantity of infections as Ross River virus disease is classified as a notifiable disease. While the official statistics indicate there are around 5,000 cases of illness across the country (there are between 500 and 1,500 cases per year in NSW), there are likely to be many more people that experience a much milder illness and so never get blood tests to confirm infection. These people won’t appear in official statistics.

What makes Ross River virus a fascinating pathogen to study is also what makes it extremely difficult to predict outbreaks. Transmission cycles require more than just mosquitoes. Mosquitoes don’t emerge from local wetlands infected with the virus, they need to bite an animal first and become infected themselves before then being able to pass on the pathogen to people.

It is generally thought that kangaroos and wallabies are the most important animals driving outbreak risk. However, we’re starting to better understand how the diversity of local wildlife may enhance, or reduce, likely transmission risk.

How was the virus found in Sydney?

The recent warnings have been triggered by the results of mosquito trapping and testing around Sydney. NSW Health coordinates an arbovirus and mosquito monitoring program across the state and this includes surveillance locations within metropolitan Sydney.

Mosquitoes are collected using traps baited with carbon dioxide. They trick the mosquitoes into thinking the trap is an animal. By catching mosquitoes, we can better understand how the pest and public health risks vary across the city and the conditions that make mosquitoes increase (or decrease) in numbers.

It mostly occurs around the metropolitan region’s northern and southern river systems and generally associated with estuarine or brackish-water wetlands. In these areas, there are often abundant mosquitoes and wildlife. Along the Parramatta River, there are often abundant mosquito populations but given the heavily urbanised landscape, there aren’t many kangaroos and wallabies.

The nuisance impacts of mosquitoes, such as Aedes vigilax, dispersing from the estuarine wetlands of the Parramatta River can create challenges for local authorities. These challenges include targeted wetland conservation and rehabilitation strategies along with ecologically sustainable mosquito control programs.

Is the detection of the virus in Sydney unusual?

The detection of Ross River virus is not that unusual. Detection of Ross River virus (as well as other mosquito-borne viruses such as Stratford virus) along the Georges River in southern Sydney is an almost annual occurrence. The local health authorities routinely issue warnings and in recent years have successfully used social media to spread their messages.

Ross River virus has also previously been detected along the Parramatta River.

While there have been confirmed local clusters of locally acquired Ross River virus in the suburbs along the Georges River, there have been no confirmed cases of Ross River virus disease in the suburbs along the Parramatta River.

There are a few reasons why more disease isn’t reported. Health authorities are active in promoting personal protection measures, sharing recommendations on insect repellent use and providing regular reminders of the health risks associated with local mosquitoes. It isn’t unreasonable to think these actions raise awareness and encourage behaviour change that reduces mosquito bites and subsequent disease.

Along the Georges River, there is clearly a higher risk of infection given the more significant wildlife populations, especially the wallabies common throughout Georges River National Park. By comparison, along the Parramatta River there are fewer bushland areas and virtually no wallabies (except for the occasional one hopping across the Sydney Harbour Bridge). Even in the wetland areas around Sydney Olympic Park, there is abundant bird life, meaning mosquitoes are probably more likely to be biting the animals than people. A study looking at the blood feeding preferences of mosquitoes in the local area found that animals were more likely to be bitten, mosquitoes actually only fed on humans about 10% of the time.

It is important that if you’re spending a lot of time outdoors in these areas, especially close to wetlands and bush land areas at dawn and dusk when mosquitoes are most active, take measure to reduce the risk of being bitten. Cover up with long sleeved shirts and long pants and apply an insect repellent. Choose a repellent that contains either DEET (diethlytoluamide), picaridin, or oil of lemon eucalyptus. Apply it to all exposed skin to ensure there is a thin even coat – a dab “here and there” doesn’t provide adequate protection. More tips here.

Also, keep in mind that just because cooler weather has arrived, the health risks associated with mosquitoes remain. That means keeping in mind that mosquitoes will be out and about just as football and netball seasons start so take along some mosquito repellent to training nights.

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Join the conversation on Twitter!

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Are mosquitoes disappearing?

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

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

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

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

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

Tracking change in mosquito populations

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

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

Mosquitoes under threat?

It is entirely possible that there are mosquitoes under threat.

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

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

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

Mosquitoes can adapt

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

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

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

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

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

 

Giant mosquitoes are invading my backyard!

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

Wetlands, climate change, and managing mosquitoes

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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