Mosquito Biology
Utah has around 50 mosquito species, out of more than 3,700 worldwide. Mosquitoes go through four life stages: egg, larva, pupa, and adult. The first three stages take place in water, and development can happen in as little as 5–7 days. The four most common groups along the Wasatch Front are Aedes, Anopheles, Culex, and Culiseta.
Life Stages
Egg.
Some females, like Culex and Culiseta, lay eggs on the water's surface in clusters called "egg rafts" containing 100–300 eggs stuck together. Aedes and Anopheles lay eggs separately. Culex, Culiseta, and Anopheles lay on the water's surface, while Aedes lay on substrate that will later be flooded by water. Most eggs hatch within 48 hours of contacting water.
Larva.
Larvae, commonly called "wigglers" or "wrigglers," live in water and breathe air from the surface. Most use siphon tubes for breathing, though Anopheles larvae have no siphon and lie parallel to the water's surface. Larvae feed on micro-organisms and organic matter, shedding their skin four times and growing larger after each molt. The stages between molts are called instars. When the 4th instar molts, it becomes a pupa.
Pupa.
Pupae, called "tumblers," are lighter than water and float at the surface. They breathe through two tubes called "trumpets." When disturbed, they dive in a jerking, tumbling motion before floating back up. Pupae don't feed. This is when the mosquito transforms into an adult, which takes about two days. When development is complete, the pupal skin splits and the adult emerges.
Adult.
Newly emerged adults rest on the water's surface to dry and harden, allowing their wings to spread before flight. Only females bite. Males feed on plant juices. Depending on the species, females may prefer one type of host or feed on a variety. Females need a blood meal to develop eggs, though some species have evolved to lay viable eggs without one.
Flight and Lifespan
Flight habits vary by species. Most domestic species stay within a mile or two of where they emerged, but some have been recorded as far as 75 miles from their breeding source. Females typically fly farther than males.
Adult lifespan depends on species, temperature, humidity, gender, and time of year. Males are typically shorter-lived than females.
Local Species
Salt Lake City has around 15 mosquito species. Several are commonly collected in the district's surveillance traps:
- Culex tarsalis
- Aedes dorsalis
- Culex pipiens
- Aedes sierrensis
- Culiseta inornata
- Anopheles freeborni
Mosquito-Borne Diseases
The district tests for three main mosquito-borne diseases: West Nile virus (WNV), St. Louis encephalitis (SLE), and western equine encephalitis (WEE).
West Nile Virus (WNV)
West Nile virus is one of the most common mosquito-borne diseases and the leading cause of mosquito-borne disease in the contiguous United States. People get WNV through the bite of an infected mosquito, with Culex (house) mosquitoes as the main spreaders.
Symptoms
About 80% of infected people show no symptomsUp to 20% develop fever, headache, body aches, nausea, vomiting, or skin rashLess than 1% develop severe infection affecting the brain and/or nervous system, causing encephalitis or meningitisSevere symptoms can include confusion, seizures, speech problems, muscle weakness or paralysis, neck stiffness, and coma. These may last several weeks, and effects on the brain and nervous system may be permanent. WNV can be fatal.
Treatment
There is no vaccine for WNV and no specific treatment. Mild cases can be managed at home with over-the-counter pain medicine to reduce fever and relieve symptoms. Severe cases may require hospital care, including IV fluids, pain management, and nursing care.
While there is no human vaccine, one exists for horses. Horses and birds are also affected by WNV.
St. Louis Encephalitis Virus (SLE)
St. Louis encephalitis virus is spread to people through the bite of an infected mosquito. Most infected people show no symptoms. Those who do may experience fever, headache, nausea, vomiting, and tiredness.
Some develop a more severe neuroinvasive infection, such as encephalitis or meningitis. Death and long-term disability are possible but rare.
There are no vaccines or medicines to treat SLE. The best protection is preventing mosquito bites.
Western Equine Encephalitis Virus (WEE)
Western equine encephalitis is spread through the bite of an infected mosquito. No human cases have been reported in the United States since the late 1990s, but the district still tests for it in mosquito populations across the service area.
Most infected people don't feel sick, though some develop fever or severe neurologic disease. There is no vaccine for WEE, so bite prevention is the best way to protect yourself.
