What is driving salt marsh mosquito peaks in Darwin: tides or rainfall?

Abstract

The northern salt-marsh mosquito Aedes vigilax (Skuse) is an established vector for Ross River and Barmah Forest viruses and an aggressive biter and an appreciable pest species in the Northern Territory (NT). Many of Darwin’s northern suburbs are adjacent to the coastal wetland of Leanyer swamp, which has an extensive breeding habitat for Ae. vigilax. Medical Entomology (ME) of the NT Department of Health conducts adult mosquito surveillance and larval mosquito control for Ae. vigilax in this wetland. One trap located near the residential suburb of Karama consistently reports some of the highest numbers of Ae.vigilax of the 7 local swamp trap locations. ME wish to clarify why it should indicate the highest numbers and what environmental variable triggers these peaks. The trap site is close to the residential area, and the results are used to trigger public warnings of mosquito pest or potential disease risks. This paper seeks to identify the most important environmental variables associated with peaks of ≥ 500 Ae. vigilax/trap/night, to better indicate the reasons for the peaks and the section of the swamp that is the source of these peaks, to reduce public pest problems and disease risks. The results of the analysis using models indicated that calendar months September - November had significantly more peaks than January and in addition to rain in these months were more associated with high monthly tides coinciding with rain. The Karama trap site is relatively close to the flood plains and wet lands associated with the Holmes Jungle section of the wetland, and the large tidal influenced swamps to the east outside the 5 km control zone. This suggests larval control should be implemented with increased emphasis in rain flooded tidal influenced areas of the Holmes jungle section of Leanyer swamp after high tides with rain events coinciding s during the build-up months between September and November. This study supports applying statistical methods to existing control programs can enable insights into solutions without the need for additional field experiments and may have applications for other mosquito control programs in other areas.