Light Pollution: A Deadly Disruptor for West Nile Virus-Carrying Mosquitoes
A recent study has revealed that urban light pollution may have a significant impact on the winter dormancy period of mosquitoes that transmit the West Nile virus. However, the discovery comes with a mix of positive and negative implications.
According to the study, the good news is that if the mosquitoes are unable to fatten up during the winter months due to the effects of light pollution, they may not survive. However, the bad news is that their dormancy period, known as diapause, could be delayed, which could lead to the mosquitoes biting humans and animals for a more extended period into the fall season.
Megan Meuti, an assistant professor of entomology at The Ohio State University and the senior author of the study, has pointed out that Ohio witnesses the highest levels of West Nile virus transmission during late summer and early fall.
She explained that if mosquitoes are unable to enter diapause as a result of urban light pollution and continue to be active for longer periods, this could increase the risk of West Nile virus transmission.
The risk would be especially high during the late summer and early fall, “when the mosquitoes are most likely to be infected with the virus, and people could be at greater risk of contracting it.”
According to the researchers, including Megan Meuti and her team, this study and previous research are among the first to demonstrate that artificial light at night could significantly influence mosquito behavior in ways that may not be easily anticipated.
“We’re finding that the same urban light at night can have very different effects under different seasonal contexts,” she points out.
Matthew Wolkoff and Lydia Fyie, both PhD candidates in entomology at Ohio State, joined Megan Meuti in conducting this study. Recently, the research was published in the journal Insects.
The study focused on the dormancy period of female Northern house mosquitoes (Culex pipiens), which is not a complete hibernation but a period of inactivity when the insects reside in semi-protected areas such as caves, culverts, and sheds. Before winter sets in, the mosquitoes convert sugary sources like plant nectar into fat reserves.
As the days become longer, female mosquitoes start searching for blood meals to enable them to produce eggs. Unfortunately, some of these mosquitoes become infected with the West Nile virus by feeding on infected birds and later transmit the virus to humans, horses, and other mammals.
The present study builds upon two previous findings from Meuti’s laboratory. During her doctoral research, Meuti observed that the circadian clock genes varied between diapausing and non-diapausing mosquitoes, suggesting that the length of the day influences the start of diapause. More recent work led by Fyie found that exposure to dim light at night prevented diapause in female mosquitoes and caused them to become reproductive even when short days indicated they should remain dormant.
In the current study, conducted by Wolkoff, the researchers investigated both lines of inquiry by examining the daily activity and nutrient accumulation of mosquitoes raised under two laboratory conditions. The first condition simulated long days similar to the mosquito’s active season, while the second condition induced dormancy through short days. The researchers also studied the impact of artificial light at night on mosquito behavior in both conditions.
The study revealed further evidence linking mosquito behavior to a circadian pattern. It demonstrated that the mosquitoes’ activity decreases during diapause, but their circadian rhythm persists during this period of dormancy.
The introduction of artificial light at night disrupted these activity patterns and impacted the mosquitoes’ ability to accumulate the necessary nutrient reserves for surviving the winter months. This nutrient accumulation is critical for the mosquitoes to fatten up and withstand the colder temperatures of winter.
The study found that exposure to light pollution hindered the accumulation of water-soluble carbohydrates, which are a vital food source for mosquitoes during the winter, in both long-day and short-day conditions. The mosquitoes’ glycogen accumulation patterns were also affected by the introduction of artificial light at night. Normally, non-dormant mosquitoes have high levels of glycogen in their bodies, while diapausing mosquitoes do not. However, in the presence of light pollution, the long-day mosquitoes did not accumulate much glycogen, and the short-day mosquitoes exhibited an increase in glycogen accumulation.
The study revealed that the impact of light pollution on mosquito activity followed a consistent pattern. While dormant mosquitoes showed a slight increase in activity, mosquitoes in the long-day condition, expected to be actively searching for food, exhibited slightly suppressed activity. Although these trends were not statistically significant, Wolkoff noted that the combined observations suggested that light pollution may disrupt diapause by interfering with the circadian clock signals of mosquitoes.
“This could be bad for mammals in the short term because mosquitoes are potentially biting us later in the season,” warns Wolkoff, “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.”
The researchers intend to conduct field studies to determine if their laboratory findings are applicable in natural settings.
These findings highlight the complex and often unforeseen impacts of urbanization on local ecosystems and public health. As the world continues to urbanize, it is essential to consider the unintended consequences of artificial light and other environmental factors on the spread of infectious diseases.
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