With COVID-19, the economy, and now social unrest in our land, we’ve all had a lot on our minds. While rightly absorbed with these critical issues, attention to a few little pest management details have fallen by the wayside around my landscape. On a recent journey behind my toolshed, I found my old Frisbee, a wheelbarrow, a five-gallon bucket and a long abandoned former fire pit filled to the brim with murky water. This should have been no surprise, what with several impressive bouts of rain we’ve had recently. Want to know the perfect recipe for creating scads of mosquitoes? Abundant rain, containers filled with decaying organic matter like leaves and flower buds, a little warm weather, and some overwintered mosquitoes like the ones nibbling my ankles a couple of weeks ago. One look into the water revealed not hundreds but thousands of tiny mosquito larvae, a.k.a. wrigglers, ready to turn into tiny vampires in a week or so. Using my mosquito sampler, I reckoned there to be roughly 2000 larvae in the fire pit. With temperatures now hitting the 90s in the DMV and throughout parts of our country, legions of female mosquitoes shall emerge from the drink and, as Paul Thomas Anderson said, “there will be blood.”
Water filled containers and drain pipes are breeding sites for mosquito larvae. Get cracking and inspect your landscape, eliminate breeding sites by inverting containers, dump bird baths twice a week, and if you cannot drain standing water kill mosquitoes where they breed with Bacillus thuringiensis israelensis.
Awhile later that day, in preparation for my joyous weekly lawn cutting event, my wife removed a drain cover in the lawn to prevent its impending destruction, one that had befallen other such drain covers levied by the blades of my lawn mower. Upon removing said cover, we were once again astonished to discover scores of mosquito wrigglers paddling about the waters of the drainpipe. How female mosquitos penetrated the gravity triggered trap door security of the drain cover remains a mystery to me. Darn clever are these tiny vampires.
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 gals have 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, 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 common house mosquito, a.k.a. Northern house mosquito, Culex pipiens, lay eggs in clusters called rafts that float on the surface of the water. Each raft may contain more than 150 eggs.
Mosquitoes are more than just a nuisance and several species here in the United States carry important diseases such as West Nile virus, Eastern Equine Encephalitis, Chikungunya, and Yellow Fever. West Nile virus has killed more than 2,600 people in the US since first detected in New York two decades ago. While most of us shrug off West Nile virus, it can be severe and even 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 repellent clothing 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. 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 reduce the number of mosquitoes flying and biting. Many traps are also available to capture and kill mosquitoes. Some, like the sensational bug-zappers, rely on a light source to attract blood seekers. However, many types of moths, flies, and beetles are attracted to light, whereas mosquitoes, unfortunately, do not use light as the primary cue 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, 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. However, much work remains before we fully understand how well these traps reduce biting rates or generally reduce mosquito populations in a broad area. Another trap called the Gravid Aedes Trap (GAT) has been used along with reduction in breeding sites on a community-wide basis with good success in several locations, including some in the DMV. These traps are partially filled with water then organic materials like hay or alfalfa pellets are added to create an infusion. The delightful aroma of this infusion is irresistible to pregnant, or, in ento-speak gravid, Aedes mosquitoes like the Asian tiger. Reminiscent of the Hotel California, mosquitoes check into the GAT but they never leave. Inside the GAT they are snared in sticky stuff or poisoned.
Mosquitoes in my back yard seem to have an ankle fetish. At double speed watch this one tank up on blood and then scram to find a place to digest its meal and turn my blood protein into mosquito eggs.
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, drain pipes that hold water, or standing water on your property that are mosquito breeding sites, 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. Battalions of biters are about to make their presence known. So snap to it, inspect your landscape and eliminate mosquito breeding sites. And get ready to protect yourself, or there will be blood.
We thank Mike Murillo for providing the inspiration for this episode. Several interesting articles 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, and “Density and diversity of non-target insects killed by suburban electric insect traps” by Timothy B. Frick and Douglas W. Tallamy, were used in the preparation of this episode.
To see how to reduce mosquito breeding and biting in a residential landscape, please visit this website: Mosquito Protection – Bite Them Before They Bite You
To learn more about mosquito repellents, how long they last, and which one might be right for you, please visit the CDC’s comprehensive mosquito repellent website, Prevent Mosquito Bites.
To learn more about how communities can band together to reduce mosquito populations by eliminating breeding sites and using GATs, please visit this website, CITIZEN ACTION THROUGH SCIENCE: COMMUNITY-DRIVEN MOSQUITO CONTROL