This was published 7 years ago
One in five Melbourne homes have mosquito-infested watertanks
By Bridie Smith Science Editor
Melburnians complaining about swarms of mosquitoes this spring need to take a good hard look at themselves. Or more specifically, at their back gardens.
Results of a CSIRO survey of almost 500 backyard rainwater tanks across Melbourne has found one in five were infested with mosquitoes - much higher than anticipated.
A DIY rainwater storage unit discovered in a Melbourne backyard. It also stores mosquito larvae. Credit: CSIRO
The biggest culprit was unmeshed overflows. Of the mosquito-infested systems identified, 60 per cent were without mesh, allowing mosquitoes to use the stagnant water as a breeding ground.
The survey conducted between February 2014 and August 2014 pre-dates the current boom in mosquito and other insects, due to a wet spring.
Mosquito larvae don't need a lot of water to develop.Credit: Darrian Traynor
Led by CSIRO systems scientist Magnus Moglia, the survey also uncovered some unusual backyard rainwater storage units - including a modified wheelie bin.
"We went into this study thinking that people would have rainwater tanks that were well-maintained and looked after," he said. "So it was a bit disappointing to see that we had these sorts of issues."
Dr Moglia's team assessed 417 sites and included inspections of the roof and gutters, pumps, switches and filters as well as talking to homeowners about how they maintain their water tanks.
After the overflows, the results showed the next most common reason tanks were not mosquito-proof was the inlet. In 22 per cent of cases the inlet mesh was found to be in such poor condition it was akin to having no mesh at all.
Stagnant water near water tanks is a mosquito breeding ground.Credit: CSIRO
Even among the tanks that were found to have working mesh covering both the inlet and the overflow, about five per cent had mosquitoes breeding in them.
"How the mosquitoes are getting in needs more investigation but it could be because the mesh has a small hole or it has not been attached properly," Dr Moglia said.
Aedes notoscriptus - better known as the common backyard mosquito. Credit: Stephen Doggett, NSW Health Pathology
It is also possible that blocked gutters allow mosquitoes to lay eggs in the pooled water, which is then flushed into the rainwater tank with the eggs during a downpour.
About one in three Melbourne households have a rainwater tank.
Sydney University medical entomologist Cameron Webb said, in the female mosquito's brief lifetime , she can lay up to 500 eggs, usually in two batches. Once laid in water, it only takes three to four weeks for the insect to go from egg to adult.
Mosquito-borne diseases such as Ross River virus and Barmah Forest virus are debilitating but not fatal. The conditions are found in Victoria - particularly in the state's north in the weeks following heavy rain.
Victorian health department figures show there have been three cases of Barmah Forest virus reported to date this year and 177 cases of Ross River virus reported so far in 2016, including two this week.
The CSIRO study has been published in The Journal of Hydrology.
Six tips for keeping mosquitoes from breeding in and around your tank
- Seal both the inlet and the overflow with proper mosquito mesh, which is available from any hardware store.
- Poor meshing is as bad as no meshing, so check it regularly and replace the mesh if it is damaged or not well fitted.
- Remember that sealing the overflow can reduce the incidence of mosquitoes by two-thirds - even if the inlet is poorly sealed.
- If your overflow water pools on an open grassy area, this can be a breeding ground for mosquitoes. Ideally, your overflow water should be diverted to a covered drain.
- Keep gutters clear of blockages. Mosquitoes can breed in small pools of water that form in a blocked gutter. The eggs can then be washed into the tank.
- Inspect the whole system regularly.