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.

Unintended consequences of wildlife conservation, could more frogs mean more mosquitoes?

We need to do all we can to protect our urban wildlife but what if the ways we do that increases mosquito risk? PhD candidate Jayne Hanford will be presenting the results of her research at the Ecological Society of Australia conference in Tasmania.

Mosquitoes can share their aquatic habitats with many other animals.

The 2019 Ecological Society of Australia conference will be held in Tasmania, 24-29 November. The conference theme, “Ecology: science for practical solutions”, is closely aligned with much of the work my collaborators and myself undertake each summer. We’re trying to ensure that recommendations on managing the pest and public health risks associated with mosquitoes is informed by the best available science.

Practical solutions to the challenges of balancing mosquito management while also ensuring positive outcomes from the environment too.

Jayne Hanford will be presenting her research in the “Field-based manipulative experiments for under-standing environmental change” symposium. She has been studying the aquatic biodiversity of urban wetlands as part of her PhD. This recent project aimed to determine what impacts management of urban wetlands to enhance conditions for local frog populations may have on local mosquito populations.

The research was undertaken at Sydney Olympic Park where an extensive network of freshwater ponds make up Narawang Wetlands. These wetlands are home to the endangered Green and Golden Bell Frog (Litoria aurea) but they’re also home to the plague minnow (Gambusia holbrooki). The plague minnow is essentially the cane toad of Australia’s waterways, introduced around 100 years ago to control mosquito populations, this aggressive predatory fish has impacted much of our local aquatic life, especially frogs. Populations of this fish need to be managed to enhance conditions for local frogs and, especially, their tadpoles.

Jayne has already found that mosquitoes avoid water bodies where the fish are found. The next step was to see how the seasonal draining of the local wetlands impacted the abundance and diversity of mosquito populations.

Immature mosquitoes and other aquatic macroinvertebrates were sampled from drained and undrained ponds within the wetland network. Once the drained ponds had been at least partially reflooded, mosquitoes were more likely to be found. This wasn’t too surprising given the results of previous experiments. Mosquitoes like to avoid habitats with fish but also, if they do lay eggs in those habitats, mosquito larvae aren’t likely to last long!

The results are useful for those authorities looking to manage waterbodies for wildlife conservation. Removal of the plague minnow may result in more suitable conditions being created for mosquitoes. It may be good for the frogs but we also know that their tadpoles aren’t eating the mosquito larvae. Strategies may be required to manage the pest and public health risks associated with local mosquitoes in these habitats.

You can catch Jayne’s work in the poster session but also as part of the symposium at 3pm on Monday 25 November in Chancellor 5!

The full abstract for Jayne’s presentation is below:

Unintended impacts of managing urban wetlands for conservation

Jayne K. Hanford^1,2*, Cameron E. Webb^2,3 , Dieter F. Hochuli¹

¹ School of Life and Environmental Sciences, The University of Sydney, Australia; ² Marie Bashir Institute for Infectious Diseases and Biosecurity, The University of Sydney, Australia; ³ Medical Entomology, NSW Health Pathology, Westmead Hospital, Westmead, Australia.

Urban wetlands are increasingly being recognised as valuable conservation resources that support significant biodiversity. Concerns around the pest and public health risks of mosquitoes will restrict how we manage these wetlands, as outbreaks of mosquito-borne diseases fuel public fear and foster dislike of mosquitoes. Understanding the ecological and public health consequences of wetland management practices is vital to maximise the conservation value of urban wetlands without negatively impacting public health. Our aim was to determine how wetland management to benefit a threatened species affects mosquitoes and aquatic biodiversity. A group of six urban wetlands in Sydney, Australia, were drained to reduce the abundance of an invasive fish, Gambusia holbrooki, and then refilled to provide breeding habitat for a threatened frog, Litoria aurea. We collected and compared aquatic macroinvertebrates, mosquito larvae, and mosquito adults from these refilled wetlands, and six adjacent undrained wetlands, on four occasions across summer and autumn. Wetland draining had a significant effect on aquatic macroinvertebrates and larval mosquitoes, although differences between drained and undrained wetlands decreased over time. Draining did not affect adult mosquito assemblages associated with the wetlands. The number of constructed and rehabilitated wetlands in urban areas continues to grow, and while conserving threatened habitats and species is imperative, our results highlight how wetland management can impact non-target species with potentially negative effects on humans. It is vital that future design and management of urban wetlands around the world also considers the impact on vectors of human disease.

 

If you’re at the conference, why not join the conversation on Twitter using the official conference hashtag #ESAus19 or reaching out to Jayne or myself!

 

 

 

 

 

 

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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How far do mosquitoes fly?

There is no single answer to one of the most commonly asked questions I’m asked. “How far does a mosquito fly?” Notwithstanding those blown long distances by cyclonic winds or transported in vehicles, the distances travelled by mosquitoes varies greatly from mosquito to mosquito. But how do scientists work it out?

My latest published research demonstrates that Australia’s saltmarsh mosquito (Aedes vigilax) flies many kilometres from urban estuarine wetlands. This has great implications for improving our understanding of their role in outbreaks of mosquito-borne disease as well as designing mosquito control programs.

There are a few different ways you can work out how far mosquitoes fly.

Firstly, given we know that mosquitoes are closely associated with certain habitats, it is sometimes possible to track back collections of mosquitoes to their preferred habitats. For example, knowing a coastal wetlands mosquito is found many kilometres away from the nearest estuarine wetland may indicate it disperses widely.

Secondly, scientists can conducted mark-release-recapture experiments. In these studies, mosquitoes are marked with some kind of substance, released, and then specimens collected in traps operated in a surrounding network can be checked to see how many of those marked mosquitoes have been recaptured and how far they’ve travelled.

In this recently published study, I marked over 200,000 Aedes vigilax with a fluorescent powder (usually used to create paint) and released them close to their larval habitats in estuarine wetlands along the Parramatta River. For the next week, I set dozens of traps around the local area hoping to recollect some of those marked mosquitoes. By scanning the mosquitoes under a UV light, the marked mosquitoes were (relatively) easily identified.

Recapture rates for these types of experiments are notoriously low. While I was only able to recapture less than 1% of those marked mosquitoes released, marked mosquitoes were recaptured many kilometres from their release point. The results demonstrated that these mosquitoes of pest and public health concern disperse so widely from saltmarsh and mangrove habitats that their impacts can be felt quite widely, highlighting the need for targeted mosquito control to minimise potentially widespread pest and public health impacts.

There is an important implication here for current “mosquito aware” urban planning strategies. The incorporation of “buffer zones” between residential developments and mosquito habitats is often proposed but this research clearly demonstrated that this strategy just isn’t practical when it comes to saltmarsh mosquitoes. They just fly too far!

While this study demonstrated marked mosquitoes were travelling up to 3km, other work I’ve done has highlighted how differently the dispersal ranges of mosquitoes can be.  In a study of yellow fever mosquitoes (Aedes aegypti) in far north QLD, we found marked mosquitoes were only traveling between 100-200m. Similarly, other work with Australian backyard mosquitoes (e.g. Aedes notoscriptus) has shown they don’t fly more than 200m. That’s still enough to fly over from your neighbour’s backyard full of mosquito breeding opportunities.

There is a practical application to this work for the management of dengue in far north QLD. Knowing that the mosquitoes involved in transmission are flying less than 200m, mosquito surveillance and control can be concentrated around the homes of those infected individuals. A great example of how understanding mosquito biology can better inform cost-effective response strategies.

There is still plenty to learn about the dispersal of mosquitoes in Australia. I’ve got some ideas so if you’re looking for a research projects, get in touch!

Check out the Journal of Medical Entomology for the full paper titled “Dispersal of the Mosquito Aedes vigilax (Diptera: Culicidae) From Urban Estuarine Wetlands in Sydney, Australia“.

The abstract is below:

Aedes vigilax (Skuse) is a pest and vector species associated with coastal wetlands and the abundance of this mosquito has been identified as contributing to increased risk of mosquito-borne disease outbreaks. As urban development continues to encroach on these coastal wetlands, pest and public health impacts are becoming of increasing concern and in the absence of broadscale mosquito control. Urban planners are looking to buffer zones and other land use planning options to minimize contact between mosquitoes and humans but gaps in the understanding of dispersal ranges of mosquitoes hamper the adoption of these strategies. A mark-release-recapture experiment was conducted to measure the dispersal of this mosquito from an urban estuarine wetland in Sydney, Australia. An estimated total of over 150,000 wild caught female mosquitoes were marked with fluorescent dust and then released. A network of 38 traps was then operated for 5 d within an area of 28 km². A total of 280 marked mosquitoes was recaptured, representing less than 1% of the estimate 250,000 marked mosquitoes released. Marked mosquitoes were recaptured up to 3 km from the release point, providing an insight into the dispersal range of these mosquitoes. The mean distance traveled by marked mosquitoes was 0.83 km, a result reflecting the greater proportion of marked mosquitoes recaptured near release point. The findings of this study indicate that effective buffer zones between estuarine wetlands and high-density urban developments would be an impractical approach to minimizing pest and public health impacts associated with this mosquito.

Join the conversation on Twitter or check out some of the other articles I’ve written on mosquitoes and other biting insects at The Conversation. You can also learn more about Australia’s wonderful mosquitoes in the award winning field guide available from CSIRO Publishing.

 

 

 

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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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?

 

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.

 

 

 

Can citizen science help stop mosquito-borne disease outbreaks?

Mosquito surveillance has been a critical component of how health authorities manage the risk of mosquito-borne disease. Data on the abundance and diversity of mosquitoes, together with activity of mosquito-borne pathogens, can guide decisions on when and how to apply mosquito control agents or issue public health warnings.

Almost every state and territory in Australia conducts seasonal mosquito surveillance. The exceptions are Tasmania and ACT, although both have had some limited investigations over the years. Even among those doing routine surveillance, the program structure varies but most include the collection of mosquitoes. This is how we can determine if it really is “the worst mosquito season ever”!

The programs are currently are working well in providing early warnings of outbreaks of mosquito-borne disease. These programs often include mosquito trapping undertaken by local governments and, occasionally, members of the public. For may years there has been a strong interest in citizen scientists undertaking mosquito sampling, particularly by some schools. The projects that I’ve been involved with have rarely got off the ground for various reasons. School holidays at the peak of mosquito season doesn’t help. Beyond that, the consumable costs of the traps we use, especially the dry-ice (carbon dioxide) used to bait the traps, can be a barrier to involvement. Dry-ice use in schools, and the associated health and safety issues, has been a cause for concern too. Finally, the fact that mosquitoes may be attracted to traps operated in school or community grounds and that these mosquitoes may be carrying disease-causing pathogens can often raise concerns.

As a result, there really haven’t been any major citizen science based mosquito surveillance programs until recently. Things are changing.

One reason local authorities are starting to turn their minds to a citizen science based approach is that the threat of exotic mosquitoes will require a shift in focus from the swamps to the suburbs. The mosquitoes that drive outbreaks of dengue, particularly Aedes aegypti and Aedes albopictus live in water-holding containers in backyards and populations are not as easily measured by traditional surveillance approaches. This is why there has been a much stronger engagement with the public in Far North QLD (a region where Aedes aegypti is present and causes occasional outbreaks of dengue) where health authorities are regularly visiting backyards looking for and controlling backyard mosquitoes

There are many reasons why citizen science is starting to come into play when it comes to mosquito surveillance more broadly. Technology is getting better (as highlighted by many smartphone apps) but also, some of the laboratory techniques are getting cheaper. This is a really critical issue.

A breakthrough in rapid testing of mosquitoes led to the development of an award winning initiative in Brisbane by Metro South Health and Queensland Health Forensic & Scientific Services. The Zika Mozzie Seeker project combines this new laboratory technique with DIY mosquito traps by the general public to help track exotic mosquitoes. In short, residents create their own mosquito trap out of a bucket or recycled plastic container, it is filled with water and placed in a yard with a small piece of paper hung inside. Mosquitoes then drop by to lay eggs on the paper. After a couple of weeks, the traps are collected and egg filled paper strips sent to the lab and tested to track the DNA of local and exotic mosquitoes. The project has been an amazing success with around 2,000 participants being involved in recent years (that adds up to about 150,000 mosquito eggs collected and tested). Luckily, no exotic mosquitoes have been detected.

But when it comes to citizen science based projects, perhaps it isn’t the mosquitoes collected (the backyard mosquito battles are fun to track though) but the awareness raised that is important. Awareness not only of the risks posed by mosquitoes, but what you can do about them through the safe and effective use of mosquito repellents and other personal protection measures. Engaging the public through citizen science may be the way to go. It doesn’t always work in reaching new audiences, as was discovered in a mosquito surveillance project in South Australia, but that doesn’t mean it won’t!

Perhaps the rise in new smartphone apps will help. There are a few out there, like the Globe Observer and Mosquito Alert. These, and other smartphone apps, deserve their own post (stay tuned). However, the significant initiative of recent years has been the Global Mosquito Alert project. Launched in May 2017, here is an extract from their media release:

The new initiative, launched under the name ‘Global Mosquito Alert’, brings together thousands of scientists and volunteers from around the world to track and control mosquito borne viruses, including Zika, yellow fever, chikungunya, dengue, malaria and the West Nile virus. It is the first global platform dedicated to citizen science techniques to tackle the monitoring of mosquito populations. The programme is expected to move forward as a collaboration involving the European, Australian and American Citizen Science Associations as well as the developing citizen science community in Southeast Asia.

With such momentum, it is an exciting time to consider the potential of citizen science in Australian mosquito surveillance programs. This is what i will be exploring in my presentation at the Australian Citizen Science Conference in Adelaide this week.

I’ll be presenting the paper on Wednesday 7 February 2018 in the “Empower with Data” session. The full abstract of our presentation is below:

The public as a partner in enhancing mosquito surveillance networks to protect public health

Craig Williams (1), Brian L. Montgomery (2), Phil Rocha (2), and Cameron Webb (3)

(1) University of South Australia, School of Pharmacy and Medical Sciences; (2) Metro South Public Health Unit, Queensland Health; (3) Medical Entomology, Marie Bashir Institute of Infectious Diseases and Biosecurity, University of Sydney

Mosquito-borne diseases are pervasive public health concerns on a global scale. Strategic management of risk requires well-designed surveillance programs, typically coordinated by local health authorities, for both endemic and exotic mosquitoes as well as the pathogens that they may transmit. There is great potential to utilise citizen science to expand the reach of current surveillance programs, particularly those centred on urban areas. There is increasing focus internationally on the role of citizen science in mosquito surveillance as evidenced by the establishment of the ‘Global Mosquito Alert’ project driven by multiple international stakeholders and citizen science associations. In Australia, new initiatives to engage the public in mosquito surveillance are emerging in multiple centres; utilizing a range of emerging field and laboratory technologies that remove previously existing barriers to community involvement. In South Australia, citizen science entomology programs have been trialed, and mosquito trapping and identification technology to expand existing trapping networks has been assessed. In suburban South-East Queensland, Zika Mozzie Seeker is linking citizen scientists into a network by using new laboratory techniques to rapidly screen for Ae. aegypti DNA in large numbers of eggs collected from DIY ovitraps,. In NSW, citizen science is being used to promote biodiversity and delineate pest and non-pest activity of mosquitoes associated with urban wetlands and surrounding suburbs. Citizen science holds great potential for public engagement activities as well as serving to enhance existing surveillance operations.

 

Join the conversation on Twitter by following Dr Cameron Webb, A/Prof Craig Williams and keep an eye on the meeting via the hashtag #CitSciOz18