Date of Award

2016

Degree Type

Thesis

Degree Name

Master of Public Health

School

School of Medical and Health Sciences

First Advisor

Associate Professor Jacques Oosthuizen

Abstract

Abstract

The mosquito control program implemented by the Shire of Kalamunda Environmental Health Service has been assessed. Mosquito species and abundance has been evaluated along with an assessment on the current level of pesticide resistance and downstream S‐methoprene levels post‐treatment. The rate of Ross River virus transmission within the Shire has also been considered, along with the relationship between local species and virus transmission.

Methodology

Floating Emergence Traps were used in 15 storm‐water gullies to determine the effectiveness of S‐methoprene briquets in prevention of adult mosquito emergence over 124 days. Samples were taken monthly from October 2014 to March 2015. Two treatment methods were assessed, application of briquet using a float, and application without a float. These were compared to untreated control gullies. The productivity of gullies was also assessed. Twenty‐five carbon dioxide light traps were deployed in a treatment area and repeated in a control area. The treatment and control areas were reversed and sampled again the following season to allow for inter‐area baseline and seasonal differences. Nine water samples were taken and analysed for the presence of S‐methoprene. Samples were taken from the outlet of chains of storm‐water gullies during the first rainfall following application of S‐methoprene briquets in the area.

Results

Storm‐water gullies have been confirmed as a significant source of mosquito breeding and are likely to be increasing the spread of Ross River virus in the area in which they are located. Mosquito breeding peaks in early November, and decreases by February as the hot dry conditions prevent large scale breeding for all species. Gullies produced a mean of 108 mosquitoes per day over the season. Culex quinquefasciatus and Aedes notoscriptus are the most abundant species within the Shire at all times in the season. Numbers of C. quinquefasciatus emerging can exceed 1600 per day per gully. A. notoscriptus breeds to a lesser extent but can still exceed 70 adults per day. Both species are container breeders known to breed profusely in close contact with human habitation.

Treatment with S‐methoprene is highly effective against both species for at least 70 days and partially effective for up to 120 days, treatment provided no control by day 124. A total of 90% control was given over the 124 days. Treatment has a significant impact on the abundance of A. notoscriptus, reducing the population by two thirds at the tail end of the season. This is likely to actively reduce the transmission of Ross River virus (RRV) within the treatment area. Overall effectiveness of the briquet is not impacted significantly by the presence or absence of a float.

Treatment of storm‐water gullies correlates with reduced abundance of Aedes notoscriptus, which is a competent vector of RRV, and was found to be an important transmitter of this disease, especially when numbers of Culex annulirostris are higher than usual. Some improvements and supplements to the program are recommended, including timing of application and gully cleaning programs, and ongoing monitoring for priority vectors and evidence of pesticide resistance.

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