An assessment of mosquito breeding and control in four surface flow wetlands in tropical-subtropical Australia.

In Queensland, Australia, the tropical-subtropical climate is ideal to promote macrophyte growth in surface flow wetlands; however, there have been concerns that constructed wetlands are potential breeding sites for disease-bearing mosquitoes. The aim of this study was to assess whether mosquitoes were breeding in these constructed wetlands, and if so, where they breed, and what parameters might influence breeding: e.g. water quality, vegetation, or macroinvertebrate communities. A study of four surface flow constructed wetlands located in different climatic regions was undertaken. Mosquito larvae were sampled using 240 ml dippers and macroinvertebrates using dip nets. The wetland with the greatest biodiversity of macrophytes and macroinvertebrates had the least number of mosquito larvae (< 1% of all dips). Samples with most mosquito larvae occurred amongst dense mats of Paspalum grass or dead Typha. Despite the presence of larvae in some parts of these wetlands very few late instars or pupae were found i.e. completion of the mosquito life cycle to adult mosquitoes was unsuccessful. This study has shown that the presence of mosquito larvae can be minimised by increasing macroinvertebrate biodiversity, by planting a variety of macrophyte types and species, excluding aggressive plant species, and maintaining at least 30% open water. Macroinvertebrates are probably a crucial factor in the control of mosquito larvae ensuring that predation of the early instars prevents or limits the development of pupae and the emergence of adults.