Relationships of the Ross River virus (Togoviridae: Alphavirus) vector, Aedes camptorhynchus (Thomson) (Diptera: Culicidae), to biotic and abiotic factors in saltmarshes of south-eastern Tasmania, Australia: a preliminary studya en_825 344..355 AbstractComprehending ecological drivers of mosquito (Diptera: Culicidae) abundance involves a broad appreciation of their abiotic and biotic determinants. Such an appreciation is important where mosquito species cause significant nuisance to humans or are vectors of infectious disease. Here, a preliminary investigation is presented of relationships between larval abundance of the Ross River virus (RRV, Togoviridae: Alphavirus) vector Aedes camptorhynchus (Thomson), in saltmarshes of Tasmania, Australia, to environmental variables, aquatic fauna and surrounding land-use. Surveys of water bodies within six saltmarsh areas were undertaken during relatively stable (dry) environmental conditions, and one saltmarsh was opportunistically re-sampled following a heavy rainfall event. This study was intended to create a baseline of information from which to launch future, more detailed and targeted investigations. Significant relationships between land-use, environmental variables and aquatic fauna among water bodies were found. Abundance of Ae. camptorhynchus larvae was relatively low across sites during dry environmental conditions, but larvae were highly abundant in water bodies at one site following heavy rainfall. Abiotic and biotic correlates (potential determinants) with larval Ae. camptorhynchus abundance differed during these two sampling periods. During dry environmental conditions larvae were negatively related to pH, turbidity, dissolved magnesium, presence of decapods and abundance of amphipods, and positively related to samphire cover. Following rainfall, larval abundance was negatively related to abundance of ostracods. Indirect relationships between land-use and abundance of Ae. camptorhynchus may exist, but more detailed investigations are required to explore this implication.

Aquatic environments can be restricted with the amount of available food resources especially with changes to both abiotic and biotic conditions. Mosquito larvae, in particular, are sensitive to changes in food resources. Resource limitation through inter-, and intra-specific competition among mosquitoes are known to affect both their development and survival. However, much less is understood about the effects of non-culicid controphic competitors (species that share the same trophic level). To address this knowledge gap, we investigated and compared mosquito larval development, survival and adult size in two experiments, one with different densities of non-culicid controphic conditions and the other with altered resource conditions. We used Aedes camptorhynchus, a salt marsh breeding mosquito and a prominent vector for Ross River virus in Australia. Aedes camptorhynchus usually has few competitors due to its halo-tolerance and distribution in salt marshes. However, sympatric ostracod micro-crustaceans often co-occur within these salt marshes and can be found in dense populations, with field evidence suggesting exploitative competition for resources. Our experiments demonstrate resource limiting conditions caused significant increases in mosquito developmental times, decreased adult survival and decreased adult size. Overall, non-culicid exploitation experiments showed little effect on larval development and survival, but similar effects on adult size. We suggest that the alterations of adult traits owing to non-culicid controphic competition has potential to extend to vector-borne disease transmission.

Two saltmarsh mosquitoes dominate the transmission of Ross River virus (RRV, Togoviridae: Alphavirus), one of Australia's most prominent mosquito-borne diseases. Ecologically, saltmarshes vary in their structure, including habitat types, hydrological regimes, and diversity of aquatic fauna, all of which drive mosquito oviposition behavior. Understanding the distribution of vector mosquitoes within saltmarshes can inform early warning systems, surveillance, and management of vector populations. The aim of this study was to identify the distribution of Ae. camptorhynchus, a known vector for RRV, across a saltmarsh and investigate the influence that other invertebrate assemblage might have on Ae. camptorhynchus egg dispersal. We demonstrate that vegetation is a strong indicator for Ae. camptorhynchus egg distribution, and this was not correlated with elevation or other invertebrates located at this saltmarsh. Also, habitats within this marsh are less frequently inundated, resulting in dryer conditions. We conclude that this information can be applied in vector surveillance and monitoring of temperate saltmarsh environments and also provides a baseline for future investigations into understanding mosquito vector habitat requirements. Journal of Vector Ecology 42 (1): 161-170. 2017.

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