Messing with the sex life of the mosquito | Environment| All topics from climate change to conservation | DW | 24.06.2014
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Environment

Messing with the sex life of the mosquito

Controlling disease-carrying mosquitoes involves spraying chemicals and draining wetlands. But by sterilizing male mosquitos through radiation, scientists are working towards a more sustainable form of pest control.

The sun's gone down and the mosquitoes are coming out. They have two just two things on their tiny minds - food and sex. Unfortunately the preferred evening meal of the female mosquito is blood, and that's where the problems between humans and these bugs begin. It's why scientists at the International Atomic Energy Agency are getting intimately acquainted with mosquitoes' sex lives.

A PG-rated description of mosquitoes mating would go something like this: The female enters the swarm. A male seeks her out, his wing-beat slowing until it matches hers. Using his large front legs he grabs her back legs and swings under her abdomen. In less than a second the lovers are joined. And then, connected, they fly slowly out of the swarm while making out in mid-air. The entire coupling can take less than 16 seconds.

Understanding this 16 second frenzy, and making sure it doesn't lead to breeding, is the challenge being tackled at the IAEA's Seibersdorf research laboratories near Vienna, Austria.

"Here you can see they are in a relaxed environment," medical entomologist Jeremie Gilles told DW, pointing proudly to a net-covered cage of black bugs, all of which appeared to be sleeping.

A man's arm reaches into a net cage full of mosquitoes (Photo: Kerry Skyring)

Scientists in Vienna breed mosquitoes in net-covered cages

"And this is where the females, after blood feeding, go to lay their eggs," he added. Because the female drinks blood - that's what it's doing when it bites into our bare skin - it's the one which spreads misery and deadly diseases such as malaria, dengue fever and yellow fever.

Nuke the males to stop the biting females

The IAEA is targeting the male mosquito using what's known as the Sterile Insect Technique, or SIT. It involves sterilizing the male insects through radiation in laboratories and then releasing them in large numbers into the wild. The method has already proven effective in controlling the screw worm, which attacks livestock, and the crop-destroying fruit fly.

Because the female mosquito mates just once in her life, while the male will mate several times, the scientists at Seibersdorf hope the technique will again prove an effective form of pest control. They point out that because it's the female mosquitoes which transmit diseases, it is best to distribute only sterilized males.

Small bites, big consequences

According to the World Health Organization, malaria kills nearly 750,000 people annually, most of them children under five living in sub-Saharan Africa and who have been bitten by the Anopheles strain of mosquito.

Reducing these deaths seems justification enough for sterilizing male mosquitoes; however research Entomologist Andrew Parker points out another reason.

"If we can reach local eradication, not global eradication but local removal of the pest species, then of course there's no longer any need to use the pesticides. So the technology lends itself very much to a substantial reduction in the use of pesticides," he said.

In Burkina Faso, a country where mosquito-borne diseases such as malaria and dengue fever are common, insecticide resistant mosquitoes are a major concern for health authorities.

"The use of insecticides in agriculture impacts resistance in the vectors (mosquitoes)" said Dr. Roch Dabire, a medical entomologist from the central African country. He explained that insecticides used to control pests in crops such as cotton are the same as those used to spray for mosquito control in houses and on bed nets.

"The development of Sterile Insect Technology will not completely replace insecticides but will complement our control strategy," he said.

A young boy lies on the ground beneath a mosquito net in Burkina Faso (Photo: Cécilia Conan)

Health authorities in Africa are concerned about mosquitoes becoming resistant to pesticides

So with two potentially important life-improving goals in mind it's not surprising the scientists are abuzz with the possibilities.

"Hopefully we can do it in a large scale and then release a whole lot of sterile male mosquitoes and if all goes well we will be able to see a drop, a drastic drop, in the number of people who are suffering from the diseases that mosquitoes pass on to people," said IAEA researcher Cynthia Nanvuma as she carefully transferred mosquitoes between net-covered cages. She added that her "little dears" were doing pretty well.

Spraying mosquitoes with mosquitoes?

If the Sterile Insect Technique is to successfully suppress reproduction of mosquitoes in the wild then sterile males will need to be released in huge numbers. Jeremie Gilles says that at the current stage of the project that has not happened.

In fact releases have only been conducted on a small scale by using local people in disease prone areas to simply spread the insects from their containers by hand. But to actually swamp the wild males with sterile males and drive populations down, Gilles is thinking outside the box.

"At the moment we are working on this aspect… and we are learning that light planes, or ultra-light (planes) and gyrocopters… we even now talk about drones," he said, adding that using aircraft to drop the sterilized male mosquitoes on to mosquitoes was the best alternative to dropping pesticides.

A sign warning of radioactivity in the mosquito lab in Vienna (Photo: Kerry Skyring)

Scientists are testing whether the radiation-sterilized male mosquitoes are still attractive to females

Competing for a mate

But what if the sterile male fails in the mate finding stakes? In a hot and steamy room known as "The Greenhouse" entomologist Jeremie Gilles walks among white tent-sized cubic shapes. They are large mosquito bedrooms made from netting.

"You take the wild male and you take the laboratory-reared sterilized male and you put them in competition for a wild female," he explains, "and you see who is the best."

For Jeremy this is a key part of the sterile insect research. There would be little point in putting millions of radiated and sterile laboratory-bred males into the environment if the female quickly learns to identify them; and gives them the brush off in favor of the wild potent male, he speculates.

The buzz from behind the nets suggests the sex appeal of the sterile males is being put to the test.

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