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Time for new arms race as mosquitoes show the -

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TONY EASTLEY: Some people just seem to attract mosquitoes. To try and protect themselves they regularly use a lot of insect repellent.

There's disturbing news this morning - especially for those mosquito magnets. Mosquitoes are evolving and becoming immune to the main weapon we have to fight them off.

Simon Lauder reports.

SIMON LAUDER: They can drive people indoors and send them into a frenzy of slapping and swiping.

For decades mosquitoes have been kept at bay by DEET, the main ingredient in most insect repellents.

Now there's evidence some mosquitoes can become resistant to it.

JAMES LOGAN: I guess mosquitoes are bad news for anybody because most of us are very attractive to mosquitoes.

SIMON LAUDER: Dr James Logan and his research team at the London School of Hygiene and Tropical Medicine covered a human arm in DEET and exposed it to mozzies. The repellent worked but later the same mosquitoes were given a second go.

JAMES LOGAN: The second time we do it, a few hours later, the mosquitoes don't respond as well to the chemical. So the chemical sort of fails by around 50 per cent the second time and we don't quite understand what's happening.

We did an experiment where we connected micro-electrodes to the antenna of the mosquito which allowed us to measure its sense of smell, if you like. And what we found was that the receptors, the smell receptors for DEET were less sensitive a few hours later, which means the chemical is having some sort of effect on the mosquitoes' sense of smell and this is something that we are going to investigate further.

SIMON LAUDER: Does this indicate that mosquitoes may be developing a resistance to DEET?

JAMES LOGAN: Well this is a short term change that we've seen in their behaviour. A few years ago we published another paper which described the genetic change that can happen, so if mosquitoes are exposed to repellents, over time they can breed to become resistant to repellents, behaviourally resistant to repellents.

This isn't something that we're seeing in the field at the moment that we know of. It's something that we are going to look for in the field.

SIMON LAUDER: And I understand this test involved a particular type of mosquito, is that right?

JAMES LOGAN: Yeah, the test involved a mosquito called Aedes aegypti. This is a black mosquito that has white stripy legs and you guys do have it over there in Australia. They can transmit Dengue Fever. They bite during the day as well so repellents are certainly very useful against those mosquitoes.

SIMON LAUDER: So does there need to be a new kind of arms race to try and come up with new repellents?

JAMES LOGAN: I think it is a good idea to be researching new repellents, for sure. New research is underway to try and find better repellents that last longer.

SIMON LAUDER: There's no need to panic. Dr Logan says DEET is still a good repellent and should be used in high risk areas.

And there's always the more traditional method. (Sound of slapping)

TONY EASTLEY: Simon Lauder reporting. And those findings are published in the journal Plos One.