By Angus Dalton
The sucking season is upon us, with warm weather and heavy rain providing the perfect spawning conditions for mosquitoes to launch their summer assault.
Why mozzies terrorise some people and ignore others isn’t clear, but there are some elements – including the colours in your wardrobe – that seem to play a role in how often you cop a bite.
And a late spring deluge across the eastern seaboard last week means there are plenty of blood-suckers coming, according to mosquito expert Dr Cameron Webb from NSW Health Pathology and the University of Sydney.
“Mosquitoes will be emerging from both freshwater and saltwater wetlands over the next couple of weeks,” he said. “And unfortunately, those numbers will be hanging around at least through into the Easter holidays. So we’ve got a couple of months of mosquito season.”
In NSW and Victoria, mosquitoes are more pesky than dangerous. But there’s still a small risk of diseases such as Ross River virus, a non-fatal but potentially severe infection that afflicts about 5000 people per year.
Mosquito-borne Japanese encephalitis, Murray Valley encephalitis and Kunjin virus also occasionally crop up in regional areas. People mostly recover, but those who acquire a severe infection can die or sustain neurological damage.
Female mosquitoes seek out a blood meal when they’re ready to lay eggs. Using an arsenal of six needles to saw into the skin, inject anti-clotting saliva and insert their flexible proboscis, they guzzle blood and excrete its water to harvest protein to nourish their eggs.
But is there anything you can do to reduce the chance of bites?
Oft-cited studies have found drinking beer and eating bananas influenced how much people were bitten, although these focused on African species not present in Australia.
The Asian tiger mosquito, which lurks in the Torres Strait, seemed to prefer people with blood type O in one study.
But the preferences of the two most problematic mozzies found in south-eastern Australia aren’t known. One is Aedes notoscriptus, the common backyard mosquito that sports white polka dots and lurks in blocked drains, bird baths and rainwater tanks.
The other is Aedes vigilax, the salt marsh mosquito, which lives in mangroves but can travel unusually far for a mozzie. They’re both implicated with the spread of Ross River virus.
What we do know is all mozzie species with a taste for humans are turned ravenous by the carbon dioxide we exhale.
Mosquito expert Dr Cameron Webb setting up a mosquito trap. The traps are packed with dry ice, which emits CO², attracting mosquitoes who think it’s the breath of an animal they can feed on.Credit: NSW Health
That’s why mosquito traps used for monitoring are baited with dry ice, which emits CO². Pregnant women breathe out about 20 per cent more CO², which is partly why some studies have found those with a baby on the way are bitten twice as much as non-pregnant women.
People who have just exercised may also be a target because they’re breathing harder. The insects are also lured by lactic acid, which is boosted by exercise, too.
Vitamin B patches, vegemite and eating garlic have all been debunked as mozzie-repellers.
“Unfortunately, all the scientific research that’s been done on how diet influences attractiveness for mosquito bites has shown that it doesn’t make much difference at all,” Webb said.
But a recent study shed light on what colour clothing seems to attract the notorious yellow fever mosquito, which is found in Queensland and also spreads dengue. Professor Jeffrey Riffell at the University of Washington reported the mosquito “loves” red and black, and avoids white and green.
Webb agreed avoiding dark colours might spare you a bite or two.
“We generally find that darker colours, particularly dark blues and blacks, seem to be more attractive to mosquitoes, probably because the mosquito might more easily recognise something that looks like a large animal walking through the environment.”
“The flipside of that is that it doesn’t mean that wearing your brightest fluorescent activewear gear out for a bush walk is going to protect you from mosquito bites because colour is probably the last thing mosquitoes are really worried about when they’re desperate for a blood meal and ready to bite.”
The only way to guarantee protection is to apply a repellent containing DEET, picardin or lemon eucalyptus oil, Webb said. Plug-in mosquito repellers and burning citronella also only get you so far.
“The secret here is that there’s nothing you can do through food or drink or exercise or medication that will make you completely immune to mosquito bites,” Webb said.
“Given that it only takes one mosquito bite to transmit the pathogens that make you sick, I think everybody, whether you think you’re a mosquito magnet or not, have to take steps to avoid mosquito bites by using repellents.”
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