Mosquitoes – A Menace to Humankind

The life cycle of a mosquito
©Ohio State University Extension, Entomology Department

by Mary Dysert - Ohio Chapter Volunteer

It’s the weekend and you’ve been enjoying a pleasant day of picnicking and hiking. With dusk fast approaching, you prepare to head back home, when you hear it. A high-pitched whining near your ear and then – Ouch! After slapping the site of the sting, you see a spot of blood on your fingers. Soon you find yourself slapping and hopping – an amusing dance – as you defend yourself from a thirsty swarm of tiny, delicate insects determined to suck your blood. Like vampires, they leave their marks – hot, red, painful bites.

Long before Bram Stoker penned his now famous horror novel, "Dracula," a different type of blood-sucking creature, the mosquito, had been plaguing humankind. For 30 million years, mosquitoes have made mankind’s outdoor activities uncomfortable, no, downright painful. Much like Count Dracula, the mosquito prefers dusk, evening, and early dawn as prime hunting times to track down its next blood meal. Only the female mosquito drinks blood. She drinks to provide protein to her eggs. Her male counterpart is a vegetarian and only feeds on flower nectar and plant juices.

She may be small and fragile, but the female mosquito is very dangerous. Vampire lore mentions rats and diseases heralding the arrival of the vampire. Mosquitoes carry disease with them, spreading it from animal to human as she indiscriminately fills her belly with blood. Even if a mosquito does not carry a disease, her bite can cause allergic reactions producing hard, itchy welts that, if scratched too much, become infected.

Mosquito Species and Habitats
There are 3,100 species of mosquitoes in the world. Of that number, 2,700 species live in the United States, with 60 of those species biting the good citizens of Ohio. Most mosquitoes are no longer than 3/8 inch.

Mosquitoes live in all parts of the globe. Adults are common near woodlands, while larvae are found in any body of freshwater: rain-filled hollow tree stumps, ponds, lakes, and rivers.

Some of their habitats might surprise you. While you’d expect to find mosquitoes in warm or tropical climates, it might surprise you to know that they also reside in colder climates. For example, mosquitoes inhabit the Arctic during its short summer season. Dense swarms attack caribou, birds, and humans; literally any warm-blooded creature they can find during their short lifecycle.

Lifecycle of the Mosquito
Unlike the blood sucking fiends dreamed up by Mr. Stoker, mosquitoes do not have a chance at immortality. Their lifecycle usually lasts fewer than three weeks, but what a busy three weeks it is!

All mosquitoes lay their eggs on the surface of water, either singly or in groups of 30 to 400 eggs in a group that forms a floating raft. The eggs hatch into larvae or "wigglers." They live at the water’s surface, breathing through an air tube or siphon. Some species’ larvae are cannibalistic – they eat other mosquito larvae. Others simply feed on organic matter. Depending on the water temperature and mosquito species, larvae live from days to several weeks.

After four molts, the larvae become pupae, or "tumblers." Pupae live in the water from one to four days, floating at the surface and breathing through two small tubes or trumpets. They do not eat. At the end of the pupae stage, they encase themselves and transform into adult mosquitoes.

Adult mosquitoes immediately mate. Male mosquitoes have huge, feather-like antennae that function as ears and are sensitive to sound waves in the air. They listen for the high-pitched hum of a flying female mosquito, caused by her wings beating between 250 – 500 times per second. (She can fly up to three miles per hour.) The whining, droning sound that keeps you awake at night is music to the male mosquito’s "ears." He follows the female, catches her and strokes her body with his legs. If the taste receptors on his legs perceive a pheromone that identifies her as a member of his species, then he will mate with her.

Female mosquitoes have only one objective – to survive and reproduce. Blood meals are required each time they lay eggs. Females mate, feed, and lay eggs for days, even weeks. Males, however, only live a few days after mating.

Time for lunch
So, just how does that blood sucker find you? The female mosquito simply responds to a sequence of cues that begins when a searching female notices and then flies to a large, dark object that contrasts with the background. If it gives off heat and carbon dioxide, she will land on it. If the smell and taste suit her, she inserts her piercing-sucking mouthparts and sucks its blood through a channel formed by her elongated labrum and mandibles.

A female mosquito’s abdomen is elegantly engineered so that as she feeds, her abdomen becomes bloated with blood. Her abdominal segments are joined to each other by membranes that allow each segment to telescope into the preceding segment. The hard upper and lower walls of each segment are joined by membranous side walls. These membranes unfold so her abdomen can expand both in length and width. That is why you’ll find blood on your hand after smacking a feeding mosquito.

Treating a Mosquito Bite
Some of the mosquito’s saliva remains in the wound after she bites you. As a result, your body initiates an immune response that causes the area to swell and itch, which remains until your immune cells break down the saliva proteins.

Wash mosquito bites with mild soap and water. Anti-itch medicines, such as cortisone or Benadryl creams, or calamine lotion, will relieve the itching. If you feel dizzy or nauseated, see your doctor.

Potential Diseases
Female mosquitoes of many species carry bacteria, parasites or viruses that cause serious diseases in animals and humans. These diseases include: Malaria, Yellow Fever, Encephalitis, and Dengue Fever. The human immunodeficiency virus (HIV) is not transmitted from one person to another through mosquito bites because the virus cannot survive in a mosquito.

Today in Ohio, catching Malaria, Yellow Fever, or Dengue Fever is next to impossible. This is changing, however, with the emergence of West Nile virus. Encephalitis, however, is present in the United States and has been contracted by Ohioans. Several types of encephalitis can be transmitted by the Aedes or Culiseta mosquitoes, including St. Louis, Western Equine, Eastern Equine, La Crosse, and West Nile. Symptoms include high fever, stiff neck, headache, confusion and sleepiness. If you’ve been bitten by mosquitoes and have these symptoms, immediately see your doctor.

Because mosquitoes are capable of transmitting diseases ranging from mild to life-threatening, controlling mosquito population growth continues to be a concern for public health officials.

Preventing Mosquito Bites
While you cannot completely avoid mosquitoes, you can reduce the number of bites and still enjoy the outdoors. You can prevent mosquito bites by:

Wearing dark clothing that covers most of your body
Applying mosquito repellents that contains NN-diethyl-meta-toluamide (DEET) or Permethrin, which is for use on clothing only
Using head nets when in heavily-infested areas, such as salt marshes
Maintaining window and door screens to keep them "bug tight"
Burning citronella oil or candles
Staying indoors during the evening when mosquitoes are most active, especially when there is a mosquito-borne disease warning

Anyone with a low resistance to infections, especially people taking immunosuppressive drugs, needs to avoid mosquito bites. According to Dr. Roger S. Nasci, a mosquito expert at the Fort Collins, Colorado, U.S. Centers for Disease Control and Prevention facility, immuno-compromised persons should use EPA-registered repellents.

Controlling Mosquito Populations
You can control the mosquito population by:

Eliminating sources of standing water in your yard – empty standing water in old tires, buckets, plastic covers, toys, or other containers.
Emptying and changing water in bird baths, fountains, wading pools, and plant trays at least once a week.
Unclogging gutters.
Treating swimming pools.
Stocking garden ponds with fish to eat the mosquito larvae. (The Ohio Department of Natural Resources discourages the use of fish that are not indigenous to Ohio.)
Using yellow outdoor lights.

If you have questions about mosquitoes and their control, call your local mosquito control district or health department.

Resources:

Mosquitoes and Disease by John McKenzie 8/6/04 ABCNEWS.com
EPA: Pesticides – Mosquitoes: How to Control Them
Ohio State University Extension Fact Sheet: Mosquitoes, by William F. Lyon, Richard L. Berry, Michael F. Collart (http://ohioline.osu.edu/hyg-fact/2000/2058.html)
How Mosquitoes Work by Craig C. Freudenrich, Ph.D. (http://science.howstuffworks.com/mosquito.htm)
When Mosquitoes Bite, flick ‘em, don’t smack ‘em by Michael Woods, Pittsburgh Post-Gazette National Bureau (http://www.postgazette.com/pg/04201/348501.stm)
The Handy Bug Answer Book, by Dr. Gilbert Waldbauer
Insects Through the Seasons by Gilbert Waldbauer
Insects: Spiders and Other Terrestrial Arthropods by George C. McGavin