Spring rains and hot days have heralded the start of Sydney's yearly mosquito invasion, with residents in riverside suburbs in particular feeling the bite.
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Helicopters are spraying mangrove forest and saltmarsh areas along the Parramatta River at Homebush in a bid to drive down "nuisance" levels of the pesky insects as the weather heats up.
Dr Cameron Webb, a medical entomologist from NSW Health Pathology, said: "Mosquitoes, like most insects, love warm weather.
"As soon as we start to get the first of those warmer days, mosquitoes spring into action."
Dr Webb said heavy rains in late October had slightly brought forward the start of this year's peak mosquito breeding season across the city.
"In Sydney, any of the areas near the Georges, Parramatta and Hawkesbury rivers will really notice a jump in mosquitoes about one to two weeks after those really high spring tides, or king tides."
But Dr Webb said other types of mosquitoes thrived in suburban backyards far from major estuaries, flocking to even tiny amounts of water left to stagnate in containers, blocked drains and gutters.
He said mosquitoes generally picked up diseases, such as Ross River virus, that sparked concern among experts, from animals such as kangaroos and wallabies in bushland areas.
"In Sydney, we don't see an increased risk mosquito-borne diseases until you get into some of the peripheral areas, such as the foothills of the Blue Mountains and around the Hawkesbury."
Ross River virus is caused by the bite of an infected mosquito and can trigger flu-like symptoms including fever, chills, headache and pains in muscles and joints.
There weren't any types of mosquitoes found in the Sydney metropolitan area that could transmit more serious diseases such as dengue fever or Zika virus, Dr Webb said.
The summertime influx of mosquitoes near Sydney Olympic Park has prompted the start of a yearly bug blitz.
Wetlands along the Parramatta River are natural breeding habitats for saltwater mosquitoes, which can reach "particular nuisance levels" in the area in warmer months, the Sydney Olympic Park Authority said.
The authority has started using ground and aerial spraying to reduce the numbers of mosquitoes for residents, workers and visitors to Newington and Wentworth Point under its yearly bug blitz.
Spraying uses bacterial larvicide, which the authority said is considered safe for humans, pets and other animals.
Dr Webb said the the program appeared to be "quite effective", with mosquito populations being reduced by 80 to 90 per cent in affected areas after spraying.
He said researchers usually found 10,000 to 15,000 "wrigglers", or immature mosquitoes, in traps before an area was sprayed, compared to no more than 1000 in each trap afterwards.
Helicopter spraying will be based on predicted tide data in the Newington Nature Reserve Wetland area and is set to take place on about eight mornings between November and April.
