WASHINGTON, May 21 -- U.S. and Chinese researchers said Thursday they have identified a gene that makes dengue- and yellow fever-spreading mosquitoes male.

Since only females of the species, called Aedes aegypti mosquitoes, feed on human blood and transmit pathogens, the discovery could set the stage for developing mosquito control strategies that convert females into harmless males or selectively eliminate deadly females, the researchers reported in the U.S. journal Science.

The male-determining gene "provides us with exciting opportunities to harness mosquito sex in the fight against infectious diseases because maleness is the ultimate disease- refractory trait," said Zhijian Tu, professor of biochemistry at the Virginia Tech, who led the study.

Male-determining genes often reside in "genomic black holes," or repeat-rich chromosome regions, which is why none had been found in mosquitoes or other insects before, Tu said.

In the new study, Tu's team, in collaboration with Xiao-Guang Chen, a professor at China's Southern Medical University, analyzed male-specific genome sequences from Aedes aegypti mosquitoes and eventually identified a candidate gene called Nix.

When the researchers injected Nix into mosquito embryos, more than two-thirds of the female mosquitoes developed male genitals and testes.

When they removed Nix using a genome-editing method known as CRISPR-Cas9, male mosquitoes developed female genitals.

"Aedes aegypti is a major vector for dengue, yellow fever, and chikungunya viruses, and only female mosquitoes feed on blood and transmit these pathogens," Tu wrote in his paper. "Thus, genetic control methods that introduce a male bias to reduce mosquito populations are attractive and potentially effective measures to reduce the incidence of mosquito-borne disease."

Aedes aegypti is an invasive species originally from Africa that first began to spread around the world by ship in the 1700s. This species is a major health problem because it is highly adapted to human environments.

"Targeted reduction of Aedes aegypti populations in areas where they are non-native could have little environmental impact, and drastically improve human health," Brantley Hall, a Ph.D. student in Tu's lab and co-first author on the paper, added in a statement.