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Mosquito populations are rising in the Northwest, as is the threat of diseases they carry. In response, scientists have gained new insight into how mosquitoes detect a common chemical in order to create more effective repellents.

A warming climate has lengthened "mosquito season" in the Northwest, in some places by more than a month.

Jeffrey Riffell, a biology professor at the University of Washington, said the problem is not just that mosquito populations are increasing; they are also becoming resistant to common insecticides.

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"These are chemicals like permethrin and others used to control local mosquito populations, or even ones that we spray on ourselves," he said. "and so we really need to find ways to prevent mosquitoes."

Riffell said his international team has identified the receptor on mosquitoes’ antenna that detects borneol, a chemical used in natural insect repellents. With this information, Riffell plans to identify new chemicals that could be even more repellent to the bugs. He said borneol smells good and is common in many aromatic plants such as rosemary.

Riffell said the team is also using CRISPR gene-editing technology to create genetically modified mosquitoes that cannot detect borneol. He explained that being able to turn off the gene that makes mosquitoes avoid the compound allows them to test how effective it is.

'When we do that, we have these mosquito strains that can't smell this borneol repellent," he said. "They don't really care anymore. Whereas the wild type that we have around us are really highly repelled."

Riffell said this work is timely because with a warming climate, mosquitoes are moving north, along with the diseases they carry. He said mosquitoes that carry dengue and zika virus are already present in California, and could be as far north as Seattle in as few as 50 years.