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Ecological factors influencing the distribution and abundance of the saltmarsh mosquito vector (Aedes camptorhynchus)

Rowbottom, RM ORCID: 0000-0002-3162-9368 2020 , 'Ecological factors influencing the distribution and abundance of the saltmarsh mosquito vector (Aedes camptorhynchus)', PhD thesis, University of Tasmania.

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A major contributor to the transmission of vector-borne disease in many countries are mosquitoes that emerge from saltmarshes. This is particularly the case for Australia, where saltmarsh mosquitoes are arguably the most important for vector-borne infections. The saltmarsh habitat influences the distribution, abundance and success of adult mosquitoes. This occurs through the intrinsic nature of environmental and ecological factors in saltmarshes and can also be impacted by anthropogenic factors. In this thesis, my research is focused on Aedes camptorhynchus, the temperate mosquito vector of Ross River virus (RRv); the most prominent and ecologically important vector-borne disease in Australia. Understanding the diversity of saltmarsh habitats and the ecology of saltmarsh mosquitoes within these habitats has potential to improve mosquito vector management and human disease.
I conducted a high-level scoping review of research literature undertaken on saltmarsh mosquito vectors in Australia (Chapter 2). I found that saltmarsh ecology, in particular the ecology of saltmarsh mosquito vectors, is poorly understood partly due to the expanse and diversity of saltmarsh habitats across the country, and the number of vectors involved in the transmission of disease. I emphasise the utility of ecological health and ecosystem function with respect to human health, vector management and the need for greater knowledge surrounding local saltmarsh ecology and mosquito vector dynamics.
In Chapter 3, I conducted a comparative study between three superficially similar temperate saltmarshes to identify how environmental conditions and aquatic invertebrate assemblage influence mosquito vector abundance. I identified distinct differences in mosquito assemblage between saltmarsh systems and seasons. Environmental variables were dominant in predicting mosquito numbers and vegetation (samphire) cover was ubiquitous among saltmarshes in predicting first instar mosquito abundance. Aquatic conditions differed in ability to predict the numbers of Ae. camptorhynchus first instars or pupae. The abundance and diversity of aquatic invertebrates contrasted between saltmarsh habitats. Saltmarshes with the least anthropogenic disturbance had greater aquatic invertebrate diversity and fewer vector mosquitoes. This work demonstrates the value in understanding natural saltmarsh aquatic ecology in the context of vector ecology and saltmarsh ecosystem health.
Having identified ecological differences among saltmarsh systems and their influence on vector abundance, I (Chapter 4) conducted a fine-scale field evaluation of the saltmarsh with the highest density of mosquito vectors to determine specific environmental drivers and locations of mosquito egg distribution. I determined that vegetation, particularly samphire (Sarcornia quinquiflora), was preferred by Ae. camptorhynchus for oviposition relative to shrubby glasswort (Tecticornia arbuscula), runnels and bare soil. No correlation between aquatic invertebrates, tidal connectivity, soil moisture and elevation on oviposition habitat selection was found. I discovered that this saltmarsh was less influenced by regular tidal inundations relative to rainfall, resulting in dryer habitat conditions. By understanding oviposition habitat selection and factors determining hatching success we can improve vector surveillance, and management efforts can be more targeted and efficient.
Lastly (Chapter 5), I investigated if a prominent ostracod micro-crustacean affected local populations of Ae. camptorhynchus. My aim was to identify if Ae. camptorhynchus competed with this abundant microcrustacean leading to changes in development and survival or if the main limitation was resources. I found that the most limiting factor for Ae. camptorhynchus survival and development was resources, rather than competition. When resources were limited it resulted in delayed mosquito development, decreased larval survival and smaller emergent adult mosquitoes. Of these three parameters only adult mosquito size changed when food resources were abundant and ostracod density increased, resulting in decreased adult mosquito size. I conclude that underlying effects of non-culicid aquatic interactions on mosquito development and survival are context dependent and could have the potential to impact vector-borne disease transmission.
In summary, the work presented in this thesis has contributed to a greater understanding of the ecology of mosquitoes in saltmarshes. This research demonstrates the complexity of superficially similar saltmarsh systems and how detailed knowledge of these systems can inform vector surveillance and management; and how aquatic invertebrate interactions within saltmarsh systems may influence vector mosquito abundance, distribution, and potentially disease transmission. The contributions I have made to temperate saltmarsh habitats and mosquito vector research provide insights into the ecology of a prominent RRv vector and the ecological significance of saltmarsh habitats. Moreover, this thesis contributes to the growing knowledge around ecosystem health, with emphasis on the requirement to understand the ecology of vectors in saltmarsh habitats and the potential impact manipulation of these habitats can have to human health through influence on vectorial abundance and life history.

Item Type: Thesis - PhD
Authors/Creators:Rowbottom, RM
Keywords: saltmarsh, mosquitoes, RRv, ecology, ecosystem health
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