Variability in mosquito community composition associated with estuarine wetlands in Northern NSW, Australia

The Northern Rivers region of NSW, Australia, is well documented as being impacted by nuisance-biting mosquitoes and mosquito-borne disease. Mosquitoes of greatest concern are those associated with estuarine and brackish water habitats associated with coastal wetlands and understanding the spatial variability in abundance and diversity will assist the assessment of risk and inform surveillance and control programs. Adult mosquito populations were sampled, using carbon dioxide baited traps, at four locations within the Richmond River estuary at Ballina, NSW, Australia, during January and February 2021. Concomitant sampling of habitats for immature mosquitoes was also undertaken. A total of 16,467 mosquitoes was collected at all sites across two sampling periods with the most abundant mosquitoes, Verrallina funerea, Aedes vigilax, and Culex sitiens, those typically associated with estuarine environments. Culex annulirostris, a mosquito associated with freshwater habitats, and Aedes notoscriptus, a mosquito associated with water-holding containers, were also commonly collected. The mosquito communities differed, in relative abundance and species richness, between the four locations. The result highlighted the need for authorities to understand the variability in productivity of potential mosquito habitats, beyond those determinants associated with vegetation communities alone, when assessing suitable locations of mosquito surveillance and integrated mosquito management.

The environmental and ecological determinants of elevated Ross River Virus exposure in koalas residing in urban coastal landscapes

Koala populations in many areas of Australia have declined sharply in response to habitat loss, disease and the effects of climate change. Koalas may face further morbidity from endemic mosquito-borne viruses, but the impact of such viruses is currently unknown. Few seroprevalence studies in the wild exist and little is known of the determinants of exposure. Here, we exploited a large, spatially and temporally explicit koala survey to define the intensity of Ross River Virus (RRV) exposure in koalas residing in urban coastal environments in southeast Queensland, Australia. We demonstrate that RRV exposure in koalas is much higher (> 80%) than reported in other sero-surveys and that exposure is uniform across the urban coastal landscape. Uniformity in exposure is related to the presence of the major RRV mosquito vector, Culex annulirostris, and similarities in animal movement, tree use, and age-dependent increases in exposure risk. Elevated exposure ultimately appears to result from the confinement of remaining coastal koala habitat to the edges of permanent wetlands unsuitable for urban development and which produce large numbers of competent mosquito vectors. The results further illustrate that koalas and other RRV-susceptible vertebrates may serve as useful sentinels of human urban exposure in endemic areas.

Observations of an unexpected abundance of estuarine mosquitoes associated with an urban freshwater wetland

ABSTRACT Urban freshwater wetlands have been identified as a potential source of mosquitoes of pest and public health concern in Australia. Mosquitoes most commonly associated with these habitats include Anopheles annulipes, Culex annulirostris, Culex quinquefasciatus, Coquillettidia linealis and Mansonia uniformis. However, adaptive management of freshwater wetlands for wildlife conservation or vegetation management can alter the local environmental conditions and may provide opportunities for other mosquito species to exploit these habitats. A series of small wetlands at Sydney Olympic Park, NSW, were drained in spring 2016 and allowed to refill via rainfall to improve conditions for the endangered green and golden bell frog Litoria aurea. Below-average rainfall was experienced that summer and the wetlands did not fully refill until early autumn. Surprisingly, immature stages of the estuarine mosquito, Aedes vigilax, were observed in the freshwater wetlands in exceptional abundances during this period. Adjacent to these freshwater wetlands there are extensive saltmarsh and mangrove habitats where highly abundant populations of Ae. vigilax are common. Observations of use of freshwater habitats by this estuarine mosquito have implications for urban freshwater wetland management and rehabilitation strategies, which currently do not consider the potential pest and public health issues associated with estuarine mosquitoes.

The Diversity and Distribution of Viruses Associated with Culex annulirostris Mosquitoes from the Kimberley Region of Western Australia

Metagenomics revealed an impressive breadth of previously unrecognized viruses. Here, we report the virome of the Culex annulirostris Skuse mosquito, an important vector of pathogenic arboviruses in Australia. Mosquitoes were collected from three sites in the Kimberley region of Western Australia. Unbiased high-throughput sequencing (HTS) revealed the presence of 16 novel viral sequences that share less than 90% identity with known viruses. None were closely related to pathogenic arboviruses. Viruses were distributed unevenly across sites, indicating a heterogeneous Cx. annulirostris virome. Polymerase chain reaction assays confirmed HTS data and identified marked variation between the virus prevalence identified at each site.

Discovery of Cocirculating Ross River Virus and Barmah Forest Virus At Wide Bay Military Training Area, Northeastern Australia

ABSTRACT An arbovirus surveillance military exercise was conducted to assess the risk of Ross River virus (RRV) and Barmah Forest virus (BFV) in the Australian Defence Force (ADF) Wide Bay training area (WBTA), northeastern Australia, in April 2018. Of the 5,540 female mosquitoes collected, 3,702 were screened for RRV and BFV by quantitative reverse transcription–polymerase chain reaction in a field laboratory. One pool of Verrallina funerea was positive for RRV and 8 pools (7 pools of Aedes vigilax and 1 pool of Culex annulirostris) were positive for BFV. Phylogenetic analysis of the complete nucleotide sequence of the E2 protein subgrouped both RRV and BFV with viruses previously isolated from human infections, indicating the potential risk of RRV and BFV infection to ADF personnel while training in WBTA. This is the 1st time that both RRV and BFV have been detected in a military training area.

Complete Genomic Sequence of an Australian Sindbis Virus Isolated 44 Years Ago Reveals Unique Indels in the E2 and nsP3 Proteins

The complete genome sequence of a Sindbis virus (SINV) strain (SINV_AUS_1975_18953) isolated in Australia in 1975 from Culex annulirostris mosquitoes revealed unique deletions in amino acid positions 182 to 184 and 201 to 228 of the E2 envelope protein and multiple indels in the nonstructural protein 3 (nsP3).

Oviposition Behavior of Culex annulirostris (Diptera: Culicidae) Is Affected by the Recent Presence of Invasive Gambusia holbrooki (Cyprinodontiformes: Poeciliidae)

Constructed wetlands are popular tools for managing threatened flora and fauna in urban settings, but there are concerns that these habitats may increase mosquito populations and mosquito-related public health risks. Understanding the interactions occurring between mosquitoes of public health concern and co-occurring organisms is critical to informing management of these habitats to mitigate potential health risks and balance the multiple values of urban wetlands. This study examined how oviposition behavior of Culex annulirostris Skuse, the most important pest mosquito species associated with freshwater wetland habitats in Australia, is influenced by the presence of Gambusia holbrooki Girard, a widespread invasive fish. Water was collected from urban wetlands that are intensively managed to reduce G. holbrooki populations to assist conservation of locally threatened frogs, and adjacent unmanaged wetlands where G. holbrooki was abundant. Laboratory experiments were conducted to examine the oviposition response by Cx. annulirostris to water samples from these two habitats. Experiments were conducted on two occasions, once in February following draining and refilling of the urban wetlands, and repeated following a substantial rainfall event in March. The results clearly demonstrate that ovipositing mosquitoes were able to detect and avoid water derived from habitats containing fish, even in the absence of the fish themselves. Understanding how invasive species affect the behavior and spatial distribution of pest species such as Cx. annulirostris will enable future wetland design and management to maximize benefits of urban wetlands and minimize potential public health risks.

Interpreting mosquito feeding patterns in Australia through an ecological lens; an analysis of blood meal studies.

Mosquito-borne pathogens contribute significantly to the global burden of disease, infecting millions of people each year. Mosquito feeding is critical to the transmission dynamics of pathogens, and thus it is important to understanding and interpreting mosquito feeding patterns. In this paper we explore mosquito feeding patterns and their implications for disease ecology through a meta-analysis of published blood meal results collected across Australia from more than 12,000 blood meals from 22 species. To assess mosquito-vertebrate associations and identify mosquitoes on a spectrum of generalist or specialist feeders, we analysed blood meal data in two ways; first using a novel odds ratio analysis, and secondly by calculating Shannon diversity scores. We find that each mosquito species had a unique feeding association with different vertebrates, suggesting species-specific feeding patterns. Broadly, mosquito species could be grouped broadly into those that were primarily ornithophilic and those that fed more often on livestock. Aggregated feeding patterns observed across Australia were not explained by intrinsic variables such as mosquito genetics or larval habitats. We discuss the implications for disease transmission by vector mosquito species classified as generalist-feeders (such as Aedes vigilax and Culex annulirostris), or specialists (such as Aedes aegypti) in light of potential influences on mosquito host choice. Overall, we find that whilst existing blood meal studies in Australia are useful for investigating mosquito feeding patterns, standardisation of blood meal study methodologies and analyses, including the incorporation of vertebrate surveys, would improve predictions of the impact of vector-host interactions on disease ecology. Our analysis can also be used as a framework to explore mosquito-vertebrate associations, in which host availability data is unavailable, in other global systems.