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

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

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

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

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

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

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

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

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

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

The presentation abstract is below:

What drives mosquito-borne disease risk in urban wetlands?

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

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

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

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

 

Taking Australian wetland research to China

My PhD student Jayne Hanford has been super busy this year. Not much more than a year into her candidature and she has already locked away a summer of research and has been presenting her findings at conferences here in Australia as well as overseas.

After recently sharing our research at the Society for Wetland Scientists Annual Conference held in Corpus Christi, Texas, USA and the Mosquito Control Association of Australia conference on the Gold Coast, Jayne is off to China for the 10th INTECOL International Wetlands Conference.

Her research is focused on understanding the links between wetland vegetation, aquatic biodiversity and mosquito populations. Better understanding of these links will assist management strategies that minimise actual and potential pest and public health risks associated with mosquitoes and urban wetlands.

Our abstract for the conference is below:

Is the Biodiversity Value of Constructed Wetlands Linked to their Potential Mosquito-Related Public Health Risks?

Jayne Hanford¹, Cameron Webb², Dieter Hochuli¹

¹School of Life and Environmental Sciences, The University of Sydney, Australia; ²Department of Medical Entomology, Westmead Hospital and The University of Sydney, Westmead, Australia

 Stormwater treatment wetlands constructed in cities can enhance the sustainability of urban biodiversity by providing wildlife refuge areas and habitat connectivity. However, the creation of wetlands for stormwater infrastructure can increase risks to public health and wellbeing by proliferating nuisance-biting and pathogen-transmitting mosquitoes. In severe cases, this proliferation can erode goodwill in the community for creating and protecting valuable wetland systems.  We compared mosquito assemblages at 24 natural and constructed urban wetlands in the greater Sydney region, Australia. Our aim was to determine if stormwater wetlands constructed with the goal to support high biodiversity value also had reduced associated mosquito risks. Wetlands were located across a gradient of urbanisation determined by surrounding human population density, and included sites with different aquatic and riparian habitat complexity and availability. Adult and larval mosquitoes and aquatic macroinvertebrates were sampled on two occasions through summer and autumn. Aquatic macroinvertebrates were used to derive health indices, as well as being a relative measure of aquatic diversity.  Diversity of adult mosquito species was high, and abundance varied greatly between wetlands. Macroinvertebrate assemblages were also highly variable between sites. Wetlands with greater habitat complexity had lower adult mosquito abundance and greater mosquito species diversity, compared to stormwater-specific wetlands with minimal available habitat. As expected, mosquito assemblages did not respond to urbanisation and aquatic macroinvertebrate assemblages per se, but appeared to respond to a complex suite of coarse and fine-scale features that may affect a wetland’s biodiversity value.  Effectively integrating wetlands into cities requires balancing their design for water infrastructure purposes, biodiversity resources and public health and wellbeing requirements. Understanding the risks as well as the benefits will enhance the value of constructed urban wetlands in sustainable cities while minimising public health risks posed by mosquitoes.

Jayne will be speaking in the “The next generation of wetland science: ecosystems, applications, and engineering” session in the Nanhu Room 1520-1530 on Wednesday 21 September.

You can keep an eye on whats happening in China by following Jayne on Twitter and checking the hashtag #IWC10

The Society for Wetland Scientists Annual Conference held in Corpus Christi, Texas, USA back in May included a paper by Jayne titled “Risky Wetlands? Conflicts between biodiversity value and public health” and prompted some great feedback and discussion among wetland scientists at the meeting. It was a successful trip and a timely reminder that I must get to one of the SWS meetings sometime soon, perhaps Puerto Rico?

Keep an eye out for Jayne’s research publications soon!