Culiseta incidens is commonly referred to as the “cool weather mosquito.” This species seldom breeds during the summer except in coastal areas.
Adults are large and dark brown to black in color. The tip of the abdomen is blunt, with white cross bands present on all abdominal segments when viewed from above.
This species occurs from Alaska to the Southern California border, primarily west of the Rocky Mountains. In California it occurs from below sea level to at least 9,500 feet elevation and has been recorded in every county.
Mosquitoes have four distinct life stages: egg, larval, pupal, and adult as seen in the illustration at the bottom. The first three stages of Culiseta (egg-pupa-larva) are spent in the water. The female Cs. incidens lays about 150-200 eggs in clusters called rafts, which float on the surface of the water until they hatch in about two days.
The eggs hatch into larvae (wigglers), which then feed on small organic particles and microorganisms suspended in the water. The larval stage usually lasts about 10 days, depending upon the temperature. Molting takes place after the completion of the larval stage, giving rise to the pupa (tumbler). This is the resting stage and feeding does not take place as the larval form is being transformed into an adult. The pupa is only active if disturbed. When the transformation is completed (this usually takes 2 days), the new adult splits the pupal skin and emerges.
Larvae are found in a wide variety of standing water sources including creeks, fish ponds, abandoned pools, stagnant and polluted waters, log ponds, reservoirs, snow pools, brackish water, horse troughs, artificial containers, and discarded automobile tires.
Under optimum conditions development from egg to adult takes about two to three weeks. All mosquito developmental times are dependent on the temperature and food values of the water in which they develop.
HABITS (ADULT BEHAVIOR)
Female Cs. incidens feed primarily on fowl and domestic animals but on occasion will bite man. Due to the limited flight range of this mosquito, most breeding sites are located near the area of complaints. Females are capable of flights up to 5 miles. Males do not bite, instead they feed on nectar and plant juices. Females may also feed on plant juices, but must obtain a blood meal in order to develop their eggs.
ECONOMIC AND MEDICAL IMPORTANCE
Cs. incidens is primarily a domestic nuisance and in some regions is considered relatively unimportant as a human pest. Successful laboratory transmission of St. Louis Encephalitis (SLE), Western Equine Encephalitis (WEE) and Japanese Encephalitis (JBE) virus does not indicate a potential medical importance for this mosquito.
PREVENTION AND CORRECTION
Whenever possible, sources of standing water should be eliminated in order to prevent egg deposition in the first place. This can be accomplished by filling, dumping, draining or ditching. Ornamental ponds and watering troughs are common sources. Containers holding water around the home should be checked weekly or emptied.
The most commonly used biological control agent in mosquito control is the mosquitofish (Gambusia affinis). Cs. incidens mosquitoes can often be controlled within a source by stocking it with fish.
At times, it may become necessary to control populations of Cs. incidens with chemicals when other methods of control have failed. Only trained mosquito and vector control personnel should apply chemical control agents. Control agencies have knowledge of the proper compounds and application techniques to assure minimal environmental side effects.
It is important to remember that chemical control provides only temporary relief and should only be used until longer lasting measures can be implemented.
Insect repellents may be useful if it is necessary to be in an area where large numbers of these adults are present. Always read and follow the directions on the label carefully when using a repellent.