Winter City Lights, Mosquito Bites
Issue 14, Volume 113
By Erica Wong
The weather has been getting warmer, the flowers are blooming, and pollen allergies are rising: spring is finally here! As you lazily soak up the sun, you feel perfectly content … OUCH! A stinging sensation pierces your skin, and you furiously itch your arm. Though you never saw the pesky creature, you are certain you were bitten by a mosquito.
Mosquitoes are ubiquitous, flying insects known for their ability to suck blood from human veins and leave behind red, itchy welts. Moreover, these creatures are the top carriers for some of society’s most potent diseases—such as the West Nile virus, malaria and Zika virus—through transmission of saliva as they extract blood. Mosquitoes cause nearly 2.7 million deaths and 500 million diseases annually, leading to understandable paranoia about these pesky creatures. Many people find relief from these irritating animals during the colder months when the presence of mosquitoes seems to cease entirely. This pattern is no coincidence, as mosquitoes fall into a hibernation-like state in the fall and winter called diapause. However, a recent discovery at Ohio State University has shown that the city lights in urban centers could negatively interfere with diapause in local mosquito populations.
Unlike hibernation, diapause is when mosquitos are in a state of suspended development to prevent the cold from harming their bodies. This process is essential for all types of mosquitoes, as they are cold-blooded, meaning they are unable to regulate their body temperature themselves and rely on the outside environment to do so. Without this process, their bodies would shut down from the shift to colder temperatures, killing off entire populations. During this period of dormancy, mosquitoes stop growing and slow down their metabolisms, which is possible only after they sequester enough additional energy reserves like glucose. These additional energy sources, which take the form of lipids, are then used during diapause to keep the mosquitoes alive for a period of two to three months. This sleep-like protection against the harsh winter is dictated by their circadian rhythms, or 24-hour biological clocks, that determine when to wake and sleep. Mosquitoes receive cues of seasonal changes like shorter daylight hours, which then directly affect their circadian rhythms’ internal structures. When the cold arrives, the mosquitoes’ circadian systems produce more melatonin, a sleep hormone that forces them into a slumber-like state. Despite this trend, a recent experiment has clarified that seasonal diapause may not create the mosquito-free haven that one would expect.
Dr. Megan Meuti and her team of researchers at Ohio State University discovered that city lights prevent mosquitoes from undergoing diapause. In their experiment, researchers compared the daily activity and nutrient accumulation of mosquitoes in a lab. In the control group, they mimicked the insects’ long days in their active season by using excess lighting. Then, they observed dormant winter conditions, either exposing the mosquitoes to artificial light or natural winter light. Researchers then determined that artificial light reduced the number of water-soluble carbohydrates—an energy reserve that mosquitoes compile for diapause—acquired.
These results indicate that the presence of artificial lighting causes mosquitoes to pause diapause, as their preparatory stage is insufficient to support their immobile state for the entire winter. Normally, in the months leading up to diapause, mosquitos prepare for their hibernation by finding additional energy reserves or protected sites. However, exposure to city lights, such as billboard signs or street lamp lights, makes the skies brighter in the winter. The increased lights confuse the mosquitoes’ natural circadian rhythms in every season. This light pollution disorients the mosquitoes’ physical and mental states, making them think that it is not yet time to prepare for diapause. As they do not collect the energy reserves needed for diapause on time, they are forced to scramble for food––also known as our blood.
Light pollution is a growing problem in the world, with a recent 49 percent increase in large cities due to the rise of electronic billboards and street, car, and public lighting. The implications of light pollution have the potential to be damaging, as it prolongs mosquitoes’ biting season. While it is not reasonable to conclude that we need to stop using artificial light altogether, we can encourage changes in lighting practices in and out of our homes. We can reduce the use of decorative lighting, change artificial lighting out for LED lights, and turn off external lights when they are not needed. When these small steps are implemented on a large scale, they have the potential to decrease light pollution and mosquito bites during the chilly winter months.