Solano County Mosquito Abatement District

MOSQUITO NOTES
Type: Foul Water Mosquito
Scientific Name: Culex stigmatosoma

General Information
Life Cycle
Habits (Adult Behavior)
Economic and Medical Importance
Control Methods

GENERAL INFORMATION
Culex stigmatosoma is commonly referred to as a “foul water” mosquito because of its association with polluted water.

Cx. stigmatosoma is a dark bodied, medium sized mosquito with a prominent white band on its’ proboscis (beak) and white bands on the tarsi (feet). It is further characterized by black scales, which form dots ”...” along the underside of the blunt-tipped abdomen.

This mosquito is found throughout the Western United States from Washington south to Mexico, Central America and Northern South America.

LIFE CYCLE
Mosquitoes have four distinct life stages: egg, larval, pupal, and adult as seen in the illustration at the bottom. The first three stages of Culex (egg-larva-pupa) are spent in the water. An adult female lays about 150-200 eggs in clusters called rafts, which float on the surface of the water until they hatch, in about two days. Females usually prefer to lay eggs in standing, polluted water such as sewage, street drainage, industrial wastes and backyard sources that include swimming pools, ornamental ponds, cooler drain-water and fouled water in containers. A wide variety of other water sources may also be infested with the aquatic stages of this common mosquito.

The eggs hatch into larvae (wigglers), which then feed on small organic particles and microorganisms in the water. Culex larvae may hang from the tip of their tail (siphon) when they feed or they may feed along the bottom, but they must return to the water surface to breathe. At the end of the larval stage, the mosquito molts and becomes the aquatic pupa (tumbler). The pupa is active only if disturbed, for this is the “resting stage” where the larval form is transformed into the adult. This may take about two days during which time feeding does not occur. When the transformation is completed, the new adult splits the pupal skin and emerges. Under optimum conditions, development from egg to adult takes about a week. However, all mosquito developmental times are dependent on the temperature and nutrients of the water in which they mature.

These mosquitoes may live for two or three weeks in summer, but under cooler conditions the females may live for several months. In areas of moderate climate, larvae may be found in every month of the year, but in areas with cold winters this species usually passes the winter as hibernating females in protected natural or artificial shelters such as cellars, outbuildings, wood piles, caves, culverts etc.

HABITS (ADULT BEHAVIOR)
Female Cx. stigmatosoma seem to prefer to feed on birds, but occasionally feed on livestock and rarely on humans. This species is capable of traveling 1-2 miles to seek a host, but is most commonly found near its’ aquatic habitat. 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
This species occasionally creates domestic, industrial and agricultural pest problems. Although Western Equine Encephalitis (WEE) has been isolated from natural populations of these mosquitoes; their reluctance to bite humans reduces their efficiency as disease carriers. This species has been identified as a carrier of West Nile virus.

CONTROL METHODS
PREVENTION AND CORRECTION:
Where possible, the best approach is to prevent mosquitoes from breeding by eliminating or modifying breeding sites. Any containers around the home that can hold rain or sprinkler water should be emptied on a weekly basis, modified not to hold water or covered to exclude mosquitoes.

BIOLOGICAL CONTROL
The most commonly used biological control agent in mosquito control is the mosquitofish (Gambusia affinis). The stocking of mosquitofish is often effective in controlling foul water mosquitoes sources such as fishponds, pools, watering troughs and sewage lagoons where water is not too polluted for fish survival. Other biological control measures are currently being investigated.

CHEMICAL CONTROL
At times, it may become necessary to control populations of Cx. stigmatosoma 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.