Light Pollution Could Extend Biting Season for Mosquitoes, Increasing West Nile Risk

The increasing problem of light pollution can have negative effects on both humans and wildlife. In people, it can cause sleep deprivation, increased stress, headaches and even anxiety.

Artificial light can attract animals like sea turtles, moths and frogs, leading them astray and making them more vulnerable to predators and exhaustion.

A new study has found that the winter dormancy period of mosquitoes that carry West Nile virus may be disrupted by urban light pollution.

This can cause mosquitoes to not survive the winter if they aren’t able to gain enough weight. It can also cause their dormancy period — called diapause — to be delayed, leading to a longer season of mosquito bites extending into the fall, Ohio State News reported.

“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,” said Megan Meuti, senior author of the study and an assistant professor of entomology at The Ohio State University, as reported by Ohio State News.

This and other earlier studies by the researcher team — which consisted of first author Matthew Wolkoff and Lydia Fyie, both doctoral candidates in entomology at Ohio State — were some of the first to demonstrate the effects of artificial light on the behavior of mosquitoes.

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

The study, “Light Pollution Disrupts Seasonal Differences in the Daily Activity and Metabolic Profiles of the Northern House Mosquito, Culex pipiens,” was published in the journal Insects.

For female Northern house mosquitoes, diapause is a period of dormancy when the insects spend their time in semi-protected places like culverts, caves and sheds. Before winter arrives, mosquitoes convert plant nectar and other sugars into fat, but start to seek out blood sources to facilitate egg production as the days get longer.

West Nile virus is transmitted when mosquitoes feed on infected birds and pass it along to mammals like people and horses.

Meuti had previously found that diapausing and non-diapausing mosquitoes had different circadian clock genes, indicating that how long the days are dictates the start of diapause.

More recently, Fyie and colleagues discovered that nighttime exposure of female mosquitoes to dim light led them to avert diapause and jump into reproductive activity, even during short winter days when they should be dormant.

In the new study, the researchers reared mosquitoes in laboratory conditions of two different types — long days when the insects would usually be active (the scientists used artificial light at night) and short days when they became dormant (no artificial light was used). They then compared the mosquitoes’ nutrient accumulation and daily activity.

The team discovered that the artificial light used at night affected the building up of nutrient reserves for the winter, as well as their patterns of activity.

The light pollution had the effect of suppressing the amount of water-soluble carbohydrates, an essential source of sugars during the winter, that had been stored up by the mosquitoes in both types of laboratory conditions.

Exposure to artificial light at night had the effect of reversing sugar accumulation patterns, so diapausing mosquitoes showed an increase in glycogen accumulation in their bodies, while non-dormant mosquitoes did not.

Among the dormant mosquitoes, the research team’s observations showed a slight increase in activity due to the light at night, and indicated a slight suppression of activity among non-dormant mosquitoes who were expected to be searching for food sources.

While those observations weren’t statistically significant, the observations as a whole indicated that light pollution causes mosquitoes to fend off diapause, possibly due to their circadian clock signals becoming confused.

“This could be bad for mammals in the short term because mosquitoes are potentially biting us later in the season, but 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,” Wolkoff said, as Ohio State News reported.

Field studies are in the works so the research team can see if their lab findings stay true in the wild.