Aussie mosquito expert Dr Cameron Webb shares the insights from his latest research into mosquito flying distances, with tips for pest managers controlling mosquitoes in backyards.
Mosquitoes are annoying but they can also be dangerous. Australia is lucky to be free of major outbreaks of serious mosquito-borne diseases such as dengue and malaria but this doesn’t mean that our local mosquitoes don’t pose a health risk. Thousands of people fall ill following a mosquito bite each year across the country.
Beyond these serious health risks, swarms of summer mosquitoes can still be disruptive to your time outdoors. Some of the fun of spending time in your backyard can be lost when you’re swatting away at mosquitoes all afternoon.
But where are they all coming from?
For most people, it is the Australian backyard mosquito (Aedes notoscriptus) that causes most of the problems. This mosquito lives in water-filled containers in our backyards, from bird baths to buckets to blocked gutters and drains. These things fill up with water after rain, eggs hatch and adult mosquitoes can be on the wing and buzzing about in a little over a week.
If you’re one of these people who keeps your property free of these water-filled containers, you still may be bitten by mosquitoes. It can be a frustrating experience, especially those diligently tipping out, covering up, or throwing out all those containers that can be home to these mosquitoes. More so, it can create frustrations for pest control professionals when mosquitoes continue to cause problems despite recent treatments.
The challenge with mosquitoes is that they can fly in across the back fence from your neighbour’s yard or local wetlands. So, how far can these pesky little blood suckers fly?
Just as mosquitoes vary in their size, colour, and propensity to bite, so too do they vary in their flight ranges.
While the mosquitoes found in our backyards may not fly more than 200 metres, some mosquitoes found in our local wetlands may fly many kilometres. Once you take into account the role of strong winds in blowing mosquitoes about, it isn’t unusual to collect mosquitoes over 20 kilometres from their known breeding spots.
So, how do scientists work out how far they fly?
As each type of mosquito favours a particular type of breeding habitat, it is possible to work out how far a mosquito has travelled by calculating the distance to nearest suitable habitat. While this may be easily done when the mosquitoes are associated with coastal wetlands, it gets a little trickier when you’re dealing with mosquitoes that may be found in freshwater wetlands and other habitats spread across a local suburb or city.
Another approach is to undertake ‘mark-release- recapture’ experiments. In these experiments, mosquitoes are collected, marked in some way, usually by a fluorescent powder, and released. Mosquitoes are then trapped again at varying distances from the release point and all mosquitoes collected can then be checked to determine how far they’ve travelled.
These ‘mark-release-recapture’ experiments have been done for a range of mosquitoes in Australia. These studies have confirmed that mosquitoes such as Aedes notoscriptus, as well as the yellow fever mosquito, Aedes aegypti, don’t travel far from their water-filled containers in backyards.
Marked mosquitoes weren’t often found travelling more than 200 metres. What’s especially interesting from some of the research conducted with Aedes aegypti is that its path of dispersal may be influenced by the local landscape, as it may be less likely to cross major roadways.
For wetland mosquitoes such as Aedes vigilax (main picture above) and Culex annulirostris, travelling over five kilometres is common. One of the most recently published studies investigated Aedes vigilax dispersing from urban mangroves along the Parramatta River. Marked mosquitoes were collected over three kilometres from local wetlands, highlighting the importance of effective mosquito management. While wetlands may be relatively small compared to the surrounding suburbs, the impact of mosquitoes flying out of them can be significant and widespread.
When planning and assessing mosquito control programs, whether that is in a backyard or wetland, consideration needs to be given to nuisance mosquitoes and the likelihood they’ll be flying into an area from a long way away, or perhaps just from a neighbouring backyard.
Authorities in central and north Queensland use this aspect of mosquito biology to ensure that mosquito control is concentrated in areas up to 200 metres around any cases of dengue fever that is detected. This strategy greatly reduces the likelihood of additional local cases of disease occurring.
For authorities charged with controlling mosquitoes dispersing from coastal wetlands, active management is required in a majority of wetland habitats up to three kilometres away from local suburbs to ensure there is substantial reduction in pest problems.
When professional pest managers are advising clients on the most suitable approaches for their backyard, it is important to consider what other sources of mosquitoes may be contributing to their problems. That large wetland many kilometres away may be the source of those pesky mosquitoes just as much as their next door neighbour’s neglected swimming pool!