Mosquitoes are more than just nuisances. As vectors of deadly and debilitating diseases like malaria anddengue fever, they pose a grave threat to people across much of the planet.

And that threat could now extend its reach in the United States, say scientists who warn that the winter dormancy period for mosquitoes that transmit the West Nile virus may be delayed, allowing the insects to feed on people longer into the fall.

A team of researchers at Ohio State University has reached this conclusion after finding that artificial light at night can affect the behaviors of mosquitos in unexpected ways..

“We see the highest levels of West Nile virus transmission in the late summer and early fall in Ohio. If you have mosquitoes postponing or delaying diapause and continuing to be active longer in the year, that’s at a time when the mosquitoes are most likely to be infected with West Nile virus and people could be at greatest risk of contracting it,” says Megan Meuti, the senior author of a new study who is an assistant professor of entomology at Ohio State University.

“We’re finding that the same urban light at night can have very different effects under different seasonal contexts,” Meuti adds.

During their winter dormancy, known as diapause, female Northern house mosquitoes (Culex pipiens) hide in caves, sheds and other protected locations. In order to survive the winter mosquitoes convert sources of sugar such as plant nectar into fat before they become dormant.

Then as days begin to get longer, females begin foraging for blood meals to produce eggs. Some insects infected with West Nile virus can then pass the virus on to people and other mammals.

This new research reinforces earlier findings that showed that light pollution makes mosquitoes active even at night.

Meuti and her colleagues have now found that the length of days dictates when diapause should start. However, female mosquitoes exposed to dim light at night tend to avert diapause and become reproductively active even during shorter days when they should normally be dormant.

In other words, artificial light at night tricks the insects into staying active.

“This could be bad for mammals in the short term because mosquitoes are potentially biting us later in the season,” says Matthew Wolkoff, a PhD candidate who worked on ths study.

There is a possible silver lining, however, according to Wolkoff.

“It could also be bad for mosquitoes in the long term because they might be failing to fully engage in preparatory activities they need to survive the winter during diapause, and that might reduce their survival rate,” the researcher notes.

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