There will be blood: Northern House Mosquito, Culex pipiens, and friends

A week or so ago, a friend asked if mosquitoes would be biting soon. I shared with her that, the week before last, my wife smashed the vanguard of home invading mosquitoes on the bathroom wall. Apparently, biting time is just around the corner. For the last two weeks on an almost daily basis, I have been watching an upside-down garbage pail lid full of leaves and water for the signs of breeding mosquitoes. Last Wednesday my search was rewarded when I discovered several Culex egg rafts and hundreds of tiny mosquito larvae swimming in the human-made mosquito nursery. With temperatures on the rise and showers predicted, blood thirsty female mosquitoes are not far behind. Taking a line from Paul Thomas Anderson’s classic film, “there will be blood”.  

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.   

During the first several days of adulthood, both male and female mosquitoes consume carbohydrate rich food such as plant nectar or aphid honeydew. For male mosquitoes, sweets remain the sole source of food, but the gal has a blood lust. Female mosquitoes use animal blood as the source of protein to produce eggs. The pregnant mosquito lays her spawn in a water-filled container such as a pail or bird bath or in pools of standing water on the ground. Some, like the ferocious Asian Tiger mosquito, Aedes albopictus, lay eggs near the water line of a container. When the vessel fills with rainwater, eggs hatch and larval development begins. Others, such as the Northern house mosquito, Culex pipiens, lay eggs in clusters called rafts that float on the surface of the water. Each raft can contain more than 150 eggs.  

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 warm temperatures predicted, adults will emerge, and yes, there will be blood.  

Mosquitoes are more than just a nuisance and several species carry important diseases such as West Nile Virus. West Nile Virus has killed more than 2,600 people in the United States since it was first detected in New York in 1999. While most of us shrug off West Nile virus if we are exposed, it can be severe and lethal to seniors and certain others. Recent research helps explain why this may be so. Our immune system plays a vital role in preventing diseases carried by mosquitoes. Cells lining our skin and mucus membranes bear specialized virus-sensing proteins called Toll-Like Receptors, a.k.a. TLRs. TLRs have the critical function of detecting invaders like West Nile virus. If TLRs detect the West Nile virus, they release additional proteins that stimulate production of chemical communication compounds called interleukins. Interleukins released into the bloodstream marshal cellular assassins called macrophages and direct them to hunt and kill cells infected with West Nile virus before the virus can multiple and make us seriously ill. Researchers have suggested that some seniors and people with compromised immune systems may lack sufficient TLRs and related immune system proteins to thwart the West Nile virus.  

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 entertaining itching, scratching, and swatting to days in the garden. Protect yourself from aggressive biters by wearing light-weight, long-sleeved shirts and pants when working outdoors. Certain brands of clothing are pretreated with mosquito repellents such as permethrin. I have worn these 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 this link 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. If you dine outdoors, place a small 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. Many types of moths, flies, and beetles are attracted to light, however, 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. Actually, blood seeking mosquitoes are 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.  

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, aka Bti. Bti comes formulated in doughnut-shaped tablets that can be placed in water to kill mosquito larvae.  

Battalions of biters are about to make their presence known. Snap to it and get rid of those breeding sites. Get ready to protect yourself or to give blood.  

Acknowledgements

 Several interesting articles, including “How the body rubs out West Nile virus” by  Nathan Seppa, “Toll-like Receptor 7 Mitigates Lethal West Nile 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, and “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, were consulted in preparing this episode.  

To learn more about the mosquitoes and how to defeat them, please view this video:

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