Who is responsible for mosquito management?

While much of the land along the Swan River is owned by State Government agencies, they do not actively undertake mosquito control. As a result, local governments, including the Town of Bassendean, take the lead in mosquito management to protect public health, reduce nuisance levels, and prevent the spread of mosquito-borne diseases.

When does mosquito management take place?

The Mosquito Management Program operates seasonally, typically from September to April, aligning with peak mosquito breeding periods. The duration may vary depending on rainfall, humidity, temperatures, and tidal conditions. Monitoring increases during warmer months when mosquito activity is at its highest.

Why doesn’t the Town use spraying or fogging?

Adulticide spraying — commonly known as fogging — is generally avoided and not supported by the WA Department of Health, unless it is a public health emergency, such as confirmed outbreaks of mosquito-borne viruses. 

This is because fogging has several key limitations:

• Non-selective – It affects more than just mosquitoes, potentially harming beneficial insects (such as bees and butterflies) and even aquatic life.
• Short-lived effectiveness – Fogging only kills adult mosquitoes present at the time of spraying, offering temporary relief without addressing the source of the problem.
• Weather-dependent – Safe and effective application requires very specific weather conditions, including low wind and no rain.
• Environmental and health concerns – If not applied properly, fogging can pose risks to the environment, wildlife, and public health.

Instead, our trained staff use a low-impact granular larvicides that are applied directly to water. The larvicides are made from a compound similar to the mosquito’s own growth hormone, which stops larvae from turning into adults.

The larvicides we use are very targeted. It doesn’t harm other animals, insects, fish or humans.

What is mosquito trapping and why does the Town do it?

Mosquito trapping is a surveillance technique used to monitor local mosquito populations. It involves placing traps baited with dry ice, which releases carbon dioxide as it sublimates - mimicking human breath to attract mosquitoes. Once captured, the mosquitoes are collected, counted, and identified to determine how many are present and which species they are.

The Town conducts mosquito trapping as part of its Mosquito Management Program. The data collected is vital for:

• Identifying potential breeding sites, based on the presence and concentration of specific species.
• Evaluating the effectiveness of larvicidal treatments applied in local areas.
• Tracking population trends, including detecting sudden spikes in mosquito numbers, known as breed-outs.

Why are mosquitoes such a problem in the Town of Bassendean, even with a management program in place?

Mosquitoes love still water— and with the Swan River, Ashfield Flats, and other wetlands nearby, the Town of Bassendean offers plenty of ideal breeding spots.

While we run a thorough, science-based mosquito management program, completely eradicating mosquitoes isn’t possible.

Here’s why:

• Nature plays a big role – Mosquito numbers can vary year to year depending on tides, rainfall, and temperature. Hot weather can speed up their breeding cycle, with mosquitoes maturing in as little as five days.
• Hard-to-reach areas – Wetlands like Ashfield Flats are large and environmentally sensitive, making full access and treatment tricky.
• Tiny and sneaky – Mosquito larvae are just 1–10 mm long and can be hard to detect. Once they reach the pupal stage, they’re no longer affected by larvicides.
• Environmental challenges – High tides and changing conditions can dilute treatments and reduce their effectiveness.

We’re doing our part by monitoring breeding sites regularly, using safe larvicides, and responding quickly to reports, but mosquitoes are persistent, and nature doesn’t always cooperate. It’s important for everyone to take steps to protect themselves and reduce breeding around their homes.

Why can’t mosquitoes be completely eradicated?

Complete eradication of mosquitoes is not possible, due to a range of environmental and biological factors:

• Natural wetlands and tidal zones provide ideal and persistent breeding habitats.
• Changing weather patterns and water movement make breeding conditions unpredictable and difficult to control.
• Mosquitoes reproduce rapidly and can travel long distances, often flying in from outside the Town’s control areas.

The focus of the Town’s mosquito management program is not eradication, but rather to significantly reduce mosquito populations, minimise the risk of disease, and enhance the comfort and wellbeing of the community.

Why are mosquitoes worse or better than other years?

While the Town of Bassendean applies a consistent mosquito management program every year, mosquito activity can vary significantly due to natural climate fluctuations, particularly:

• La Niña seasons bring increased rainfall and higher tidal activity, creating ideal conditions for mosquito breeding.
• El Niño seasons are typically drier, with fewer tides and stagnant water bodies, resulting in lower mosquito numbers.

These year-to-year differences are driven by broader weather systems and environmental factors beyond the Town’s control—not by changes in the management program or its effectiveness.

Why are tidal wetlands a problem for mosquito breeding?

Tidal wetlands, such as Ashfield Flats, provide ideal mosquito breeding conditions.  These natural environments are difficult to manage due to several key factors:

• High tides activate dormant eggs buried in wetland soils, triggering mass hatching events.
• Shallow, stagnant pools form after tides recede, providing ideal habitats for larvae to develop.
• Warm temperatures and high humidity accelerate the mosquito life cycle, allowing populations to explode quickly.
• Unpredictable tidal patterns result in frequent and ongoing breeding cycles, often with little warning.

Together, these conditions make tidal wetlands a persistent and complex challenge for mosquito control efforts.

What types of mosquitoes are found in the wetland areas?

Two mosquito species are of primary concern:

• Aedes camptorhynchus – Common in spring and autumn; breeds in brackish wetlands
• Aedes vigilax – Dominant in summer; an aggressive day-biting mosquito capable of flying up to 100km

Both species can transmit Ross River virus and Barmah Forest virus although locally acquired cases are rare in the Town of Bassendean.

Can mosquitoes from outside the Town affect local residents?

Yes. Many mosquito species, particularly Aedes vigilax, can fly long distances – some as far as 100km from their breeding sites. This means that even if the Town controls local breeding areas, mosquitoes from neighbouring suburbs can still impact residents. This is why regional collaboration is essential.