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

homebushbay_mangroves_jan2016

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.

 

The buzz of bat conservation

Illustration by Golly Bard (http://www.etsy.com/shop/GollyBard?ref=seller_info)

Illustration by Golly Bard (Check out some of the other wonderful illustrations of plants and animals by Golly Bard at her Etsy site)

What is the ecological role of mosquitoes?

There is a huge gap in our knowledge of mosquitoes and their place in the world. There are very few studies that have investigated what environmental “good’ they may do. This would actually be a pretty handy thing to find out. A better understanding of their ecological role may assist balancing the objectives of mosquito control and wetland/wildlife conservation that all too often appears to be (or is perceived to be) in conflict. The results of our newly published study in PLoS ONE may help in understanding the ecological role of one mosquito species in coastal wetlands.

There have been plenty of studies that have documented mosquitoes in the diet of a range of animals such as predatory aquatic macroinvertebrates, fish, frogs, lizards, birds and bats. However, the importance of mosquitoes in the diet of these animals either hasn’t been quantified or can often be overstated. One example often cited is that tadpoles eat mosquito larvae. When we tested some common Australian tadpoles, results demonstrated that they rarely consume mosquito larvae. We need to build our understanding of how important mosquitoes are (or perhaps are not) to local ecosystems.

There are almost 80 species of bat in Australia. While fruit bats may be the most commonly encountered, insectivorous bats are a less well known but diverse group of bats. These often tiny bats (often weighing less than 10g) are usually found in small and far less conspicuous groups. Many of them are found in close proximity to humans and many even be present in in major cities like Sydney. Many are listed as threatened or endangered.

The management of these bat species faces many challenges. Notwithstanding the threat of urbanisation and direct impacts on roost and foraging habitats, indirect impacts may also be important. One potential prey in the diet of bats that may be regionally important is the mosquito. Could broadscale mosquito control programs impact local bat populations?

Saltmarshes have already been identified as important habitats for the saltmarsh mosquito, Aedes vigilax. The abundance of these mosquitoes can dramatically increase in response to tidal flooding of coastal wetlands and nuisance-biting impacts can be widespread in the local community as these species disperse widely from local wetlands. This mosquito is also the major vector of Ross River virus in coastal Australia. There are about 5,000 cases of human illness caused by Ross River virus each year across Australia.

An example of saltmarsh habitats in Empire Bay, Central Coast, NSW

An example of saltmarsh habitats in Empire Bay, Central Coast, NSW

Mosquito-borne disease is an ongoing concern in many parts of Australia, particularly coastal regions. There is a range of environmentally sensitive mosquito control strategies available that have been demonstrated to provide effective mosquito control without directly adversely impacting the local environment. However, studies have shown that it is preemptive, not reactive, mosquito control efforts that have a significant impact on reducing mosquito-borne disease risk. Some concerns have been expressed by local authorities regarding the potential indirect non-target impacts on insectivorous bats of reducing local mosquito abundance.

In 2007, a multidisciplinary research project, funded by a research grant from the NSW Environmental Trust, kicked off to investigate the importance of saltmarsh mosquitoes to local bat populations on the Central Coast of NSW. The 4 year project included researchers from the Australian Catholic University, University of Sydney and Forest Science Centre (NSW Department of Primary Industries). The hard work in this project was done by PhD candidate Leroy Gonsalves (Dr Gonsalves now!).

Leroy Gonsalves (Photo ACU Media)

Leroy Gonsalves (Photo ACU Media)

The project was undertaken in a region where mosquitoes had been identified as both a nuisance-biting problem and potential public health risks but local authorities were reluctant to undertake broadscale mosquito control. For full details, see the Living with Mosquitoes document I produced for local councils in the region.

Our previously published studies analysing bat call recordings have shown that the activity of insectivorous bats can be influenced by the abundance of prey as well as the structure of local habitats. Bats use sound for the detection and capture of prey, as well as navigation, and, as calls are species-specific, an analysis of recordings can determine the bat species present in local habitats and what they’re doing there.

In this newly published paper, we radio-tracked Vespadelus vulturnus (little forest bat), a species known to be a predator of saltmarsh mosquitoes. The activity of these radiotracked bats could be monitored across a range of habitats (including saltmarsh and adjacent coastal swamp forest) when mosquito populations were at naturally relatively high and low abundances.

Bats were collected using harp nets set along flyways in the coastal swamp forest close to the estuarine wetlands. The collected bats were then fitted with small radio-transmitters and released. The activity of each bat was tracked over a period of up to 10 days whereby triangulating the signal direction could record where the bats were active, as well as allowing the identification of day roost sites. This data was then analysed together with prey (mosquito and moth) abundance data recorded using light and carbon dioxide baited traps.

An example of a harp net set to collect microbats (Photo Doug Beckers)

An example of a harp net set to collect microbats (Photo Doug Beckers)

The results were interesting.

When mosquito abundance was high, the saltmarsh was selected preferentially for foraging instead of the coastal swamp forest. However, at times of low mosquito abundance, the bats spread their activity across a range of habitats. The results suggest that this species of bat may be moving into habitats of high mosquito abundance to feed.

Little Forest Bat (Vespadelus vulturnus) (http://museumvictoria.com.au/melbournemuseum/discoverycentre/wild/victorian-environments/dry-forest/little-forest-bat/)

Little Forest Bat (Vespadelus vulturnus) (Photo: Melbourne Museum)

This is the first radio-tracking study to demonstrate a shift in habitat use by an insectivorous bat species in association with fluctuations in the abundance and distribution of a particular prey population. The shift in habitat use by the little forest bat suggests that, for this species, the saltmarsh mosquito may be an important food item (at least at times when mozzies are abundant).

Does this mean that broadscale mosquito control activities should stop? There is no doubt that the results of our research indicates that the little forest bat moves into areas where the saltmarsh mosquito is abundant. However, whether reducing the abundance of mosquitoes will have ecological implications is yet to be shown. The bats in our study site certainly weren’t eating enough to reduce nuisance-biting impacts of the mozzies!

The Saltmarsh Mosquito (Aedes vigilax) (Photo: Stephen Doggett)

The Saltmarsh Mosquito (Aedes vigilax) (Photo: Stephen Doggett)

The implications for wetland management are likely to change from location to location. In areas where there is abundant alternative prey such as moths, or mosquitoes not targeted by control activity, are present, reducing populations of key pest species like the saltmarsh mosquito may be achieved without any significant ecological impact. It is important to note that there is no evidence from our studies that the little forest bat is targetting the saltmarsh mosquito specifically. That mosquito was most abundant in this local area but in some regions along the coast, there are equally abundant mosquitoes (e.g. mosquitoes associated with freshwater or brackish water environments), many of which are not the focus of control efforts.

Perhaps an adaptive management approach is required whereby careful monitoring of bat populations is recommended and that, in areas where local bat populations may be shown to be susceptible, avoid control activities during the lactation period of bats, a time when their energetic demands are greatest. As these periods generally fall in late spring and early summer, as opposed to peak periods of  mosquito-borne disease risk that generally fall in late summer and early autumn, an integrated approach to management of both public health and environmental health can be achieved.

One of the key findings, with implications for further research directions and mosquito management, is that species-specific studies are required to understand the ecological role of mosquitoes. This result indicates that the importance of local mosquitoes for insectivorous bats is likely to be specific species (perhaps both the bat species and mosquito species), as well as no doubt varying from region to region. Managing not just the habitats but the insects associated with them may be important. Maintaining suitable habitats for bats under the pressures of expanding urbanisation along much of coastal Australia is critical. It will take more than just retaining these remnant habitats, it will be the strategies used to manage these wetlands and surrounding habitats that will also be important.

You can read the media release regarding this project and publication at the University of Sydney news page.

The full citation for our new paper is: Gonsalves L, Law B, Webb C, Monamy V (2013) Foraging Ranges of Insectivorous Bats Shift Relative to Changes in Mosquito Abundance. PLoS ONE 8(5): e64081. doi:10.1371/journal.pone.0064081