Mosquito numbers have dropped dramatically in coastal Queensland this year and locals have Mother Nature to thank.
- Scientists report sharp drop in mosquito numbers, especially in flood-affected coastal regions
- Queensland Health data shows mosquito-borne virus numbers are well below average for this time of year
- Residents are warned to remain vigilant with population explosion likely as temperatures rise
Constant downpours have disrupted typical breeding patterns, and health data shows it has also slowed the spread of many mosquito-borne diseases.
On the Sunshine Coast, council officer Mark Call said mosquito larvae in the area’s waterways had declined by up to 80%.
Mr Call said while the rain generally created better breeding grounds for the pests, this year there were simply too many.
“There is something in the region of 2 meters of rain over a period of four or five months along the coastal fringe in particular,” Mr Call said.
“There was too much rain for mosquitoes to breed in many areas, so we did less spraying and mosquito control than in drier years – so that was quite interesting to see.”
Mr Call said intense rain had impacted mosquitoes breeding in the salt marshes, which were most abundant on the Sunshine Coast.
“That the water isn’t salty enough, or one theory is that natural predators have a chance to move in as well,” Call said.
“Fish species, dragonflies, natural predators are increasing in numbers, and just don’t let mosquito larvae breed in large numbers.”
Salt marsh mosquitoes also needed a “drying period” for their eggs to heal before they hatched.
“When you get, essentially, five months of fairly consistent time, those eggs just don’t have a chance to heal.”
Don’t count the mozzies before they hatch
CSIRO lead researcher Paul De Barro said the reprieve from biting insects may not last long.
A warmer spring could lead to a population explosion.
“Winter has been particularly cold and so this will slow down the development of mosquitoes,” said Dr De Barro.
“If we are expecting our third La Niña, we can expect the conditions that existed last year in the spring and summer, which will allow mosquitoes that react to flood-like conditions to breed.”
Only female mosquitoes about to lay eggs bite humans and Dr De Barro said mosquito control needs to be balanced.
“They’re important in a healthy ecosystem, so getting rid of mosquitoes isn’t necessarily a good thing,” the scientist explained.
“They are involved in a whole range of ecological functions, in particular the larvae chewing up detritus in the water, thereby recycling dead plant matter.
“Mosquitoes can act as pollinators and they are also important food sources for a whole range of species, from invertebrate predators to birds and bats.”
Dr De Barro said CSIRO would be watching closely whether the warmer weather had caused a resurgence of the mosquito-borne Japanese encephalitis virus after an outbreak earlier in the year.
Virus down, but stay alert
The observations of Mr Call and the CSIRO are reflected in figures from Queensland Health, which show a significant drop in mosquito-borne illnesses across the state.
There have been 622 Ross River virus infections so far this year, compared to a five-year average of 1,593.
Infections in Barmah Forest fell to 138, from an average of 175.
Cases of malaria and dengue fever are also significantly lower, although the diseases are usually contracted abroad.
Despite the drop in infections, health authorities are warning residents to take steps to protect themselves.
Public health physician Marion Woods, of Sunshine Coast Hospital and Health Service, said it only took one bite to contract a deadly or debilitating virus.
“We know that Japanese encephalitis has entered Queensland and New South Wales, all the way to Victoria,” Dr Woods said.
There have been two confirmed cases of the life-threatening virus in Queensland this year.
“It’s a very serious disease…in symptomatic people it can be severe and life-threatening,” Dr Woods said.
“Simple measures of wearing mosquito repellent and light colored clothing are very helpful in reducing the number of mosquito bites.”
Mosquito control programs generally intensify in the spring as temperatures rise.
Mark Call said residents should also ensure containers with standing water are emptied to prevent freshwater mosquitoes from breeding.