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Bryce Peters, from the Insect Research Laboratory at the University of Technology, Sydney, probes the world of a well known insect pest – the mosquito. |
| Mosquitoes like humidity and warmth and an ideal habitat would be a humid, fetid swamp. Mosquitoes begin life in the water as eggs which develop into larvae (wrigglers) before becoming pupae (tumblers) and eventually adults. Only female mosquitoes take blood meals, whereas males eat sugar and nectar from flowers.
The females need the blood to produce eggs and do not travel far from their breeding sites, which, for humans, means reducing the possibility of breeding sites around their homes. Blocked gutters are a classic mosquito breeding site, as are pot plants and buckets, so most people bitten by mosquitoes have bred them themselves.
Left: Mosquito larvae
Image from AQIS, photographer Luke Halling
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Mosquitoes like it wet but even the dry places in Australia, like Broken Hill and Alice Springs, do produce large numbers of mosquitoes in a short time after rain. In Australia’s north, places like Darwin, Cairns and Townsville have mosquitoes constantly and mosquito controls have to be put in place to make living there bearable.
While they clearly thrive in the wet season, they also thrive after king tides, activating the pre-laid eggs. Australia has mosquito species that breed well in brackish water and one, Aedes vigilax, our salt marsh mosquito is very common in areas around Sydney as well as the mangroves all the way to the top end. It can deal with water that is brackish as well as water with salt concentrations, having a high tolerance for different salinity levels.
There's considerable debate about whether pest insects will increase because of climate change but Bryce thinks that if places become drier, such as the big cities, then we will see a reduction in mosquitoes. Two definite adverse increases are the rise in Ross River cases and the number of people contracting dengue fever in Cairns recently, with over a thousand cases.
Insect borne diseases are increasing worldwide. Staggeringly, every thirty seconds a child dies of an insect borne disease with millions more affected. Many die from malaria, others from yellow fever and dengue fever but treatment is problematic as mosquitoes and drugs can become resistant. Interestingly, Bill Gates contributes a lot to research into mosquito borne diseases.
Bryce’s own research, at Humpty Doo in the Northern Territory, takes place immediately after the wet season ends, usually around March. Huge numbers of mosquitoes emerge, (among them Anopheles, Culex and Mansonia) protected from predators by the fast growing grasses. The research team can trap twenty mosquitoes per minute providing a large test population which helps to discriminate between treatments. Repellents, like the iconic Aeroguard, contained the active repellent DEET which has been used safely since the 1950s. DEET is however, an excellent solvent which is why some repellents feel sticky and why the colour is washed out of plastics and vinyls if contact is made by people wearing the repellent.
A new active repellent, picaridin, is being used by some brands and is kinder to human skin. There are now some good aerial repellents which act like high-tech mosquito coils. A pad, impregnated with insect repellent, sits inside a lantern. When a candle is lit inside the lantern, the impregnated pad heats up, releasing the repellent. One will last for about four hours, protecting an area as large as 25 square metres.
Sounds like companies are onto another good thing.
Text: V.B. November 2009
Visit the NSW Arbovirus Surveillance and Vector Monitoring Program photo gallery to view an extensive series of images of all life stages of Australia's mosquito species.
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