Mosquitoes can develop an immunity to DEET and breed offspring that are also impervious to the bug repellent, scientists in England report.

Female mosquitoes use their antenna to zero in on humans in their hunt for blood to fertilize their eggs. DEET is believed to interfere with their ability to smell. A DEET-resistant mosquito would still be able to detect the savoury human smell it’s looking for.

“There is something in the antenna they use to smell that reacted differently,” Dr. Nina Stanczyk of Rothhamstead Research, the largest agricultural research centre in the U.K., told the Star on Tuesday.

Scientists studying mosquitoes in a laboratory realized some “weren’t detecting the smells of DEET.” When researchers bred those mosquitoes, the new generation could smell through the DEET as well.

DEET, developed in 1958, is little understood but highly effective in repelling mosquitoes.

“There’s been an awful lot of research on this subject” of repellents, said Stanczyk. “This could give us a greater understanding of how DEET works and how to develop new repellents.”

Stanczyk cautions that her research is limited to a laboratory, although she’s keen to extend it to field work. Outside of a laboratory, the only ideal breeding ground for DEET-resistant mosquitoes would be somewhere that everyone was wearing the repellent, she said.

Researchers also studied only one species of mosquito, the yellow fever and dengue-carrying Aedes aegypti. Canada, Bermuda, Chile and Uruguay are the four countries in the Americas not infested with A. aegypti.

“This research is very interesting but we don’t think it will lead to a worldwide failure of repellents,” she said. “People should keep protecting themselves so they don’t catch diseases.”

The findings are published in the May 3 edition of the journal Proceedings of the National Academy of Sciences.