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.

 

 

 

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.

 

Social media and blood suckers showcased at the International Congress of Entomology

Digital technology is changing a lot about how we undertake entomological research and communicate the results of that research to the community and policy makers.

This week in Orlando, Florida, is the International Congress of Entomology (ICE). A huge gathering of entomologists from around the world. While it was a great pleasure to be invited to participate, I couldn’t get over there this time.

I will, however, have a chance to present my work in the Symposium “Entomology in the Digital Age”  Friday, September 30, 2016 (01:30 PM – 04:45 PM), Convention Centre Room W222 A.

In the presentation I’ll share some of the reasoning behind my use of social media to engage the community with both entomological research and public health communication. Most importantly, it will focus on some of the metrics I’ve recorded alongside my use of social media, maintaining a blog of research and writing for outlets such as The Conversation.

I’ve written about my use of social media and how it can help extend the reach of public health messages and presented on the topic alongside a range of great speakers at the 2014 Entomological Society of America meeting in Portland.

This time around, technology is playing an even more direct role in my presentation! I’ve pre-recorded my presentation and it will be shown to the audience on the day among other presentations. I’ll also be checking into the session to answer questions. Despite the fact I’ll need to be up around 1:30am due to time differences, it should be fun.

See the abstract below…

Taking entomological research from the swamps to the suburbs with social media

Cameron E Webb

Connecting scientists and the community is critical. This is particularly the case for medical entomologists working in the field of mosquito-borne disease where the translation of entomological research into improved public health outcomes is a priority. While traditional media has been the mainstay of public health communications by local authorities, social media provides new avenues for disseminating information and engaging with the wider community. This presentation will share some insights into how the use of social media has connected new and old communications strategies to not only extend the reach of public health messages but also provide an opportunity to promote entomological research and wetland conservation. A range of social media platforms, including Twitter, Instagram, and WordPress, were employed to disseminate public health messages and engage the community and traditional media outlets. Engagement with the accounts of traditional media (e.g. radio, print, television, online) was found to be the main route to increased exposure and, subsequently, to increased access of public health information online. With the increasing accessibility of the community to online resources via smartphones, researchers and public health advocates must develop strategies to effectively use social media. Many people now turn to social media as a source of news and information and those in the field of public health, as well as entomological research more generally, must take advantage of these new opportunities. doi: 10.1603/ICE.2016.94611

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If you’re at ICE, you can also catch up with my PhD student David Lilly who’ll be presenting our research into the development of insecticide resistance in bed bugs as part of the symposium “New Insights into Biology, Resistance Mechanisms, and the Management of the Modern Bed Bug” Friday, September 30, 2016, 01:30 PM – 04:45 PM, Convention Center, West Hall F4 (WF4).

Novel insecticide resistant mechanisms in the common bed bug, Cimex lectularius

David Lilly, Cameron E Webb and Stephen Doggett

Introduction: Research on field strains of Cimex lectularius from Australia has identified widespread resistance to pyrethroid insecticides, but variability in the magnitude expressed. To determine if differences in resistance mechanisms exist, collected strains were examined for the presence of metabolic detoxification and/or cuticle thickening. Methods: The presence and relative contribution of detoxifying esterases or cytochrome P450 monooxygenases were assessed. Bed bugs collected from Parramatta (NSW), Melbourne (VIC) – 2 strains, ‘N^o.2’ and ‘N^o.4’, and Alice Springs (NT) were exposed in topical bioassays employing deltamethrin and two pyrethroid synergists: piperonyl butoxide (PBO) and EN16/5-1. PBO inhibits both monooxygenases and esterases, whereas EN16/5-1 will inhibit esterases only. Thus in a comparative bioassay, the results can infer the dominant enzyme system. The Parramatta strain was then selected to study the potential presence of cuticle thickening. Nine-day-old male bed bugs were exposed to filter papers treated with the highest label rate of Demand Insecticide^®(200mL/10L of 25g/L lambda-cyhalothrin) and were grouped according to time-to-knockdown (< 2 hours, ≥ 4 hours, and survivors at 24 hours). Measurements of mean cuticle thickness at the transverse midpoint of the second leg tarsus were taken under electron microscope. Results/Conclusion: All strains possessed resistance that was inhibited by the synergists, with the Parramatta and Melbourne N^o.2 indicating esterase-dominance, and Alice Springs and Melbourne N^o.4 indicating cytochrome P450 monooxygenase-dominance. Cuticular measurements demonstrated that bed bugs surviving deltamethrin exposure had significantly thicker cuticles, denoting a novel form of resistance in these insects. doi: 10.1603/ICE.2016.92553

 

You can also see Stephen Doggett (co-author and photographer of A Guide to Mosquitoes of Australia) speaking on photographing mosquitoes to in the symposium “Insect Photography Symposium: Bringing the Small to the World.”

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You can join the conversation on Twitter and keep an eye on all the fun in Orlando by keeping an eye on the tweet stream!