Page last updated at 15:05 GMT, Tuesday, 22 December 2009

Sex intervention combats malaria

Anopheles mosquito
Anopheles mosquitoes spread malaria

Scientists believe it may be possible to combat malaria by interfering with the sex lives of the mosquitoes which spread the disease.

They have shown that the insects can only mate successfully if the male is able to seal his sperm inside the female using a "mating plug".

Without the plug, fertilisation cannot occur, and the animals cannot reproduce.

The Imperial College London study is published in the journal PLoS Biology.

The researchers focused on the species of mosquito primarily responsible for the transmission of malaria in Africa - Anopheles gambiae.

These insects mate only once in their lifetime, so disrupting the reproductive process offers a good way of dramatically reducing their numbers.

This could be one more weapon in the arsenal against malaria
Dr Flaminia Catteruccia
Imperial College London

When they mate, the male transfers sperm to the female followed by a coagulated mass of proteins and seminal fluids known as a mating plug.

This plug is not found in any other species of mosquito and its role had previously been unclear.

But the Imperial team showed it was essential for ensuring sperm is correctly retained in the female's sperm storage organ, from where she can fertilise eggs over the course of her lifetime.

In the lab, the researchers were able to stop successful reproduction by preventing the formation of the plug in males.

Not a simple barrier

Lead researcher Dr Flaminia Catteruccia said: "We have shown that the male mating plug is not a simple barrier to insemination from rival males, as has been previously suggested.

"Instead, we discovered that the plug plays an important role in allowing the female to successfully store sperm in the correct way inside her, and as such is vital for successful reproduction.

"Removing or interfering with the mating plug renders copulation ineffective.

"This discovery could be used to develop new ways of controlling populations of A. gambiae mosquitoes, to limit the spread of malaria."

The researchers stopped the plug forming by knocking out a key enzyme which causes the seminal fluids to coagulate into a gelatinous solid mass.

Another weapon

Dr Catteruccia said: "If in the future we can develop an inhibitor that prevents the coagulating enzyme doing its job inside male A. gambiae mosquitoes in such a way that can be deployed easily in the field - for example in the form of a spray as it is done with insecticides - then we could effectively induce sterility in female mosquitoes in the wild.

"This could provide a new way of limiting the population of this species of mosquito, and could be one more weapon in the arsenal against malaria."

Professor Steve Lindsay, of the London School of Hygiene and Tropical Medicine, said any attempt to control mosquito populations could be hindered by the fact that the insects' mating behaviour was still not fully understood.

He said: "This is a very novel idea, which is really neat. We will need a whole variety of different tools to combat malaria, and this may have a function, but there is no one magic bullet."

A team at the International Atomic Energy Agency (IAEA) are working on another method to reduce the growth of the mosquito population - using radiation to sterilize male insects.

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