Mosquito management program

Mosquito management program

There are dozens of different mosquito species present in the greater Sydney metropolitan region, and most pose little concern to people. The saltmarsh mosquito, Aedes vigilax, is the most important pest mosquito in the coastal wetlands of NSW; it is a severe nuisance-biting pest and disperses widely from its saltwater wetland breeding grounds. Sydney Olympic Park is one of several locations along the Parramatta River where this species breeds.

Mosquito breeding season

Mosquitoes have complicated lifecycles – they hatch from eggs and spend the first part of their life in water feeding on organic matter before developing into adults.  The process of developing from egg to larvae to adult takes about eight to ten days.  Only adult female mosquitoes bite as they need blood to develop their eggs.  Mosquitoes also feed on nectar and plant juices and so play an important role in plant pollination, as well as being food for bats, frogs and birds.

Saltwater mosquitoes are active during the warmer months, and their population peaks during summer and early autumn. 

The table below shows the pattern of nuisance-biting mosquito activity that usually occurs at Sydney Olympic Park.

A/Prof Cameron Webb (NSW Health Pathology)

Predicting population peaks

The wetlands of Newington Nature Reserve and a part of Badu Mangroves are the main areas of Sydney Olympic Park where saltwater mosquitoes breed in high numbers.  They also breed in many other estuarine wetlands along the Parramatta River.

Population increases are triggered by very high tides or rainfall that inundate the estuarine wetlands where mosquitoes lay their eggs. Research has shown that tides over 1.8metres high result in mosquito population increases at Sydney Olympic Park, but the magnitude of those population increases depends on the number and actual height of tides over 1.8metres. Additionally, rainfall of 50 millimetres or more within three days may also trigger a hatch of mosquito larvae. Mosquito hatches will be largest when rainfall and tidal flooding occur at the same time.

What we are doing to manage mosquitoes

Sydney Olympic Park Authority, NSW National Parks and Wildlife Service and scientists from NSW Health Pathology Department of Medical Entomology together conduct a scientifically-based mosquito management program at Sydney Olympic Park between November and April each year, when the risks of nuisance-biting impacts are greatest. 

The program involves aerial and ground-based application of an environmentally-friendly mosquito control agent in mosquito breeding hotspots.

The current treatment program was established in 1998 and combines aerial (drone) and ground-based application of the control agent Bacillus thuringiensis israelensis (Bti).  Bti is a bacterium-based product that when eaten by mosquito larvae, destroys their gut wall and kills them, preventing them from developing into biting adults.  Bti is highly specific to mosquito larvae and safe to people, pets and the environment when applied at recommended rates. It is one of the most widely used mosquito control agents by authorities in Australia to reduce mosquito activity and no significant adverse environmental impacts have been reported.

This program is supported by works to improve tidal flushing of degraded wetlands, thereby reducing the area of mosquito-breeding habitats.  Over the past 20 years, mosquito populations have reduced significantly as a result of these improvements. These initiatives have demonstrated that by improving the health of the wetlands, the number of mosquitoes can be minimised. Unfortunately, these approaches are not suitable for all areas of saltwater wetlands.

Treatment timing

Mosquito treatment dates are highly dependent on tides, rainfall and temperature.  Bti needs to be applied at a specific stage of the mosquito life cycle to be effective and there is a very narrow window where treatments will be effective.  It only works on mosquito larvae treated within a few days of hatching – it does not work on older larvae, pupating larvae or adult mosquitoes. We cannot “pre-treat” the wetlands prior to inundation by tides or rainfall.

Throughout the warmer months, scientists regularly assess the extent of wetland inundation and the abundance of newly-hatched larvae at fixed monitoring sites across the estuarine wetlands.  This data is used to determine the need for Bti application.  Treatment dates are only confirmed and advised a day or two in advance, based on this on-ground monitoring. Between five and eight treatments are usually applied each season.

The effectiveness of each treatment is assessed based on comparison of pre- and post-treatment larval densities, as well as changes in the relative abundance of adult mosquitoes caught in mosquito traps.  

Mosquitoes and disease

While saltwater mosquitoes play a role in transmitting pathogens, such as Ross River virus, that cause mosquito-borne disease,  the risks of mosquito-borne disease at Sydney Olympic Park is low because of the absence of  the animals, such as kangaroos and wallabies, that that most commonly carry these pathogens.  Nuisance biting is the key impact that saltwater mosquitoes pose to people along the Parramatta River. 

NSW Health monitors the activity of mosquito-borne pathogens, such as Ross River virus, at sites across NSW, including Sydney, between December and April each year as part of the NSW Arbovirus Surveillance and Mosquito Monitoring Program. 

What can you do to stop mosquito bites?

Mosquitoes that bite will also be found in your backyard, balcony, and garden. There are mosquitoes found in water holding containers such as potted plant saucers, bird baths, drains, gutters, rainwater tanks, and other objects left outside that may fill with rainwater. Ensuring that these objects are routinely emptied, cleaned up, or stored under cover will prevent mosquitoes breeding around your home.

Mosquitoes should be expected to be active around wetlands and bushland areas during the warmer months. They are most active at dawn, dusk, and during the evening. When outdoors, cover up with light coloured, loose fitting long sleeved shirts, pants, and covered shoes. Applying an insect repellent that contains diethyltoluamide, picaridin, or oil of lemon eucalyptus will also reduce the chances of mosquito bites.

Further information

• Mosquito Spraying Application Map
• Mosquito Awareness and Protection Flyer
• NSW Arbovirus Surveillance and Mosquito Monitoring Program
• Pesticide use notification

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