Scientists in the United States said on Tuesday they had taken a major step toward developing a “mosquito birth control” drug to curb the spread of malaria and other killer diseases blamed for hundreds of thousands of deaths a year.

Researchers at the University of Arizona said they had discovered a protein unique to female mosquitoes which is critical for their young to hatch.

When the scientists blocked the protein the females laid eggs with defective shells causing the embryos inside to die.

The team said developing drugs which targeted the protein could provide a way to reduce mosquito populations without harming beneficial insects such as bees.

“It’s an important discovery. We’re certainly excited about it. This gets around mosquito resistance and also has a much better chance of being bio-safe (than other methods),” says Roger Miesfeld, head of the university’s department of chemistry and biochemistry.

Miesfeld said current methods of controlling mosquitoes had been used for so long that the insects were becoming resistant.