April mosquito management

Published on 31 March 2022

Mosquito Helicopter Treatment

Mosquitos are a fact of life in the Shire of Murray, but the 2021/22 mosquito season has been one of the worst on record.

Why are mosquito numbers so high this year?

When there are high tides, brackish water floods the banks of the Estuary or rivers, producing large areas of mosquito breeding. 

Usually high tides above 0.76 metres (the threshold for mosquito breeding in our area) persist through winter, and then drop off at other times of the year. However for the last couple of years these high tides have persisted through spring, summer and autumn.  For example, tides of 1 metre were experienced last weekend. 

For the Stakehill area in particular, tides in recent years have often been higher than average. They have moved further up the Serpentine River compared to the Harvey Estuary than in previous years, and this has also impacted mosquito numbers.

The combination of high tides and specific environmental conditions can lead to intense mosquito breeding periods, such as the one we are currently experiencing. In those unusual situations, it may not be possible to reduce the number of naturally occurring mosquitos to below nuisance levels.

We recognise that mosquito numbers are high at the moment, but the program is serving to reduce numbers significantly and we hope to see a noticeable reduction in mosquito impacts as we continue treatments and move into cooler temperatures.  

What we have done

We understand the impact mosquitos can have on lifestyles in our part of the world, and how challenging it can be to live alongside them. Over the years the Shire has invested in a number of activities and programs to help manage the number and impact of mosquitoes in our area, including:

  • Becoming a member of the Peel Mosquito Management Group (PMMG)

    The PMMG is the largest mosquito management partnership of its type in Western Australia. Along with the Shire of Murray, its members include the Department of Health, City of Mandurah, City of Rockingham, Shire of Waroona and the University of Western Australia.

    Working together, we all contribute to the operation of mosquito management, and without the PMMG, mosquito-borne disease would be more prevalent and mosquito populations would be much larger than they are in our region.
  • Adapting a predominantly airborne response plan
    Most mosquito breeding areas in the Shire are difficult to access by vehicle because they are in swampy areas on the edge of the Peel-Harvey Estuary, the Murray or the Serpentine River. In total, we have around 600 hectares of mosquito breeding areas.

    Consequently, we choose to undertake most of our mosquito treatments by helicopter to cover larger areas more quickly and more often.
  • Employing a full-time Mosquito Control Officer
    Our team monitors tides and mosquito larvae activity every day, including public holidays and weekends, and those reports inform the spraying plans ensuring they happen at the optimal time.

    We also:
    • Monitor mosquito breeding sites for larvae to understand the most impactful time to treat an area
    • Monitor mosquito breeding sites for larvae after they have been treated to ensure the success of the treatment
    • Monitor adult mosquito numbers by trapping to inform treatment plans. This activity is how we know that our larvicide spraying program reduces the number of mosquitoes by between 80% and 90%
  • Spraying regularly

    So far in 2022 we have undertaken 11 days of spraying, covering almost 2000 hectares including one of the largest single spray events we’ve ever done.

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What we plan to do

Over the last two years, the Shire has spent three times its usual budget on larvicide spraying and does this in the best interest of the community.

We are requesting additional resources from Council this month that would pay for even more larvicide and spraying as a response to the ongoing high numbers of this naturally occurring insect.

Our Mosquito Control Officer will also continue to collect data seven days a week that helps inform the spraying program and we will continue to work with the wider Peel Mosquito Management Group to align our activity across the region.

We are also undertaking a large spray at the end of March/ start of April of around 500 hectares. This is again one of the largest spray activities we will have carried out in recent years.