Hungry Northern House mosquitoes, vectors of West Nile virus, are thriving and on the hunt for blood.
As we enter the month of August, it’s high time to protect yourself from mosquito borne illnesses like West Nile Virus. In mid-July a local news agency reported the detection of West Nile Virus in mosquitoes in two counties of central Maryland. Although no human cases were detected at that time, as of the third week of July, the Centers for Disease Control (CDC) reported more than 90 cases of human disease in 20 states with Arizona and Texas leading the way. As record heat continues in our land, generation times shrink for mosquitoes. More mosquitoes are produced in shorter periods of time. Also linked to global warming is the fact that like many insects, mosquitoes become active earlier in the year and their activity continues later in the year. Scientists found that between 1979 and 2022 in cities throughout the United States higher temperatures have greatly increased the number of days each year that are warm enough for mosquitoes to bite. In San Francisco, California, the number of “biting days” has increased by 43 days since 1979. As the tropical storm season ramps up, drenching storm systems create abundant breeding sites for aquatic mosquito larvae. Together, heat and rainfall provide the perfect storm for elevating populations of mosquitoes in many parts of our nation. Let’s learn a little more about mosquitoes, the risks they pose, and how to avoid their bites and the illnesses they carry. The following is revised from a previous episode of Bug of the Week.
Not much to say about this video. Watch as a female Culex pipiens form molestus extracts all the blood she needs to produce the next batch of eggs and then scurries away to the shadow of a knuckle to hide. Filmed at twice life speed.
“Mosquitoes are more than just a nuisance and several species carry important diseases such as West Nile Virus. According to the CDC, following its discovery in the United States in 1999, more than 63,000 cases of West Nile Virus have been reported and more than 3,300 deaths associated with West Nile Virus have occurred. While most of us shrug off West Nile virus with little or no symptoms, it can be severe and lethal to seniors and certain others. Researchers have suggested that some seniors and people with compromised immune systems may lack sufficient immune responses to thwart the West Nile Virus.
Historically, August is the most common month to contract West Nile Virus. Image courtesy of Centers for Disease Control
Many species of mosquitoes prefer to feed at dusk, and you can avoid being bitten by staying indoors in the evening. Unlike many of our native mosquitoes, the exotic Asian Tiger is a daytime biter, adding hours of itching, scratching, and swatting to days in the garden. Protect yourself from aggressive biters by wearing lightweight, long-sleeved shirts and pants when working outdoors. Certain brands of clothing are pretreated with mosquito repellents such as permethrin. I wore these clothes in tropical rainforests where mosquitoes were ferocious and they really did help. Many topical insect repellents can be applied to exposed skin before you go outdoors. Some will provide many hours of protection, while others provide virtually none. Some repellents should not be applied to children, and you should always help kids apply repellents. Do not apply repellents containing DEET under clothing. To learn more about mosquito repellents, click here to see repellents recommended by the Centers for Disease Control. For safety, be sure to read and follow the directions on the label of the repellent before you apply it to people or clothing.
Asian tiger mosquitos are active during daylight hours. They vector important human diseases including dengue, chikungunya, and Zika.
If you dine outdoors, place a fan on your patio. The light breeze created by the fan will greatly reduce the number of mosquitoes flying and biting. Many traps are also available to capture and kill mosquitoes. Some rely on a light source to attract blood seekers. However, many types of moths, flies, and beetles are attracted to light. Mosquitoes, unfortunately, do not use light to find their meals and are not readily attracted to light traps. One study demonstrated that less than 1% of the insects attracted to light traps were biting flies such as mosquitoes. This study estimated that light traps kill billions of harmless and beneficial insects each year. Blood seeking mosquitoes are actually attracted to odors emanating from the host. As we move about the earth, we release many odors, including carbon dioxide and lactic acid, that are used by hungry mosquitoes to find us. Some mosquito traps release carbon dioxide and will catch many mosquitoes. Female mosquitoes ready to lay eggs are attracted to odors emanating from water sources. A clever trap called a Gravid Aedes Trap (GAT) has been used in community-wide programs in the DMV to reduce local populations of Asian Tiger mosquitoes. Females fly into these traps to lay eggs but never escape. Sounds like Hotel California for these tiny vampires.
A garbage pail lid full of water becomes the perfect nursery for a crop of Culex mosquitoes. Two egg rafts contain scores of eggs ready to hatch. Nearby, fleets of mosquito larvae called wrigglers filter tiny particles of food from the water. In just a few short weeks, this lid will be bustling with fully developed wrigglers suspended beneath the water by breathing siphons. Amidst the milieu, zany mosquito pupae called tumblers bumble about. With continued hot weather and ample rainfall, adults will emerge, and yes, there will be blood.
To reduce the chances of mosquitoes breeding around your home, eliminate standing water by cleaning your gutters, dumping your bird bath twice a week, inverting your wheelbarrow, and getting rid of water filled containers. If you have an aquatic water garden or standing water on your property that breed mosquitoes, you can use a product containing the naturally occurring soil microbe known as Bacillus thuringiensis israelensis a.k.a. Bti. Bti comes formulated in doughnut-shaped tablets that can be placed in water to kill mosquito larvae. With continued hot weather and ample rainfall, mosquitoes will be present for several more months. Be on the lookout and take precautions now to avoid being bitten.”
Wheelbarrows and pails full of water - dump them now! They are nurseries for mosquito larvae.
Acknowledgements
We thank Dr. Megan Fritz for loaning us one Culex mosquito to record feeding on blood. Several interesting articles were consulted for this episode including, “How the body rubs out West Nile virus” by Nathan Seppa, “Toll-like Receptor 7 Mitigates Lethal West Nile and Encephalitis via Interleukin 23-Dependent Immune Cell Infiltration and Homing” by Terrence Town, Fengwei Bai, Tian Wang, Amber T. Kaplan, Feng Qian, Ruth R. Montgomery, John F. Anderson, Richard A. Flavell, and Erol Fikrig, “Density and diversity of non-target insects killed by suburban electric insect traps” by Timothy B. Frick and Douglas W. Tallamy, “Neighbors help neighbors control urban mosquitoes” by Brian J. Johnson, David Brosch, Arlene Christiansen, Ed Wells, Martha Wells, Andre F. Bhandoola, Amy Milne, Sharon Garrison & Dina M. Fonseca, and “Mosquito days’ are on the rise, courtesy of global warming” courtesy of the Carey Institute of Ecosystem Studies. Information on the geographical and seasonal occurrences of West Nile Virus came from the data rich CDC websites.
To learn more about the mosquitoes and how to defeat them, please view the following video: https://youtu.be/mSRw4MnHaX8
