Saltmarsh, mosquitoes and insectivorous bats: Seeking a balance

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Coastal saltmarsh provides suitable breeding habitat for a number of estuarine mosquito species. The saltmarsh mosquito (Aedes vigilax Skuse) can be locally abundant throughout summer, representing a potentially important prey resource for insectivorous bat species. However, Ae. vigilax has been identified as an important vector of mosquito-borne viruses such as Ross River virus and Barmah Forest virus and is a known nuisance biting pest. Coastal residential areas adjacent to Empire Bay (e.g., Killcare, Pretty Beach and Hardys Bay) on the Central Coast of New South Wales, Australia are prone to nuisance biting from Ae. vigilax and other estuarine mosquito species, particularly in late summer each year. Residents have requested use of a broadscale mosquito spraying regime (using Bacillus thuringiensis israelensis, Bti) to control numbers of Ae. vigilax. While it has been suggested that Ae. vigilax may be an important dietary item for insectivorous bats foraging within saltmarsh, no study to date has specifically investigated the importance of the mosquito in the diet of these bats. In this thesis, I investigated the importance of Ae. vigilax to insectivorous bats on the NSW Central Coast by examining relationships between bat activity, habitat use by bats, bat diet and the availability of Ae. vigilax and non-mosquito prey in three major habitats (saltmarsh, urban and forest) within the area. In all, 15 bat species and two species groups were recorded, of which eight are listed as threatened under the NSW Threatened Species Conservation Act (1995). Bats were most active in forest habitat, however, proportional feeding activity was greatest in saltmarsh. Positive relationships between prey abundance and total bat activity were only detected in the less cluttered saltmarsh habitat.