Solano County Mosquito Abatement District

MOSQUITO NOTES
Type: Winter Mosquito
Scientific Name: Culiseta inornata

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

GENERAL INFORMATION
Culiseta inornata is commonly referred to as the “winter mosquito” and seldom breeds during warm weather.

Adults are large, light brown in color and appear to have wings without scales, which makes them easily distinguishable from other mosquitoes. The tip of the abdomen is blunt, with no inconspicuous patches or scales on the wings and the unscaled cross veins midway in the wing are nearly in line. The males of this species are noticeably smaller than the females and lack the bushy antennae of most other male mosquitoes. In addition, the males have long palpi on their heads, and “claspers” at the tip of their abdomen. This species is widely distributed through out the State.

This species occurs throughout most of North America from sea level to over 10,000 feet in altitude. Larvae are found in a wide variety of aquatic habitats from fresh water to salt marshes.

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 Culiseta (egg-larva-pupa) are spent in the water. The female Cs. inornata 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. Feeding may take place at the bottom or near the water surface. Breathing takes place at the water surface and is accomplished by means of orienting upside down with the tip of their tail (siphon) pointing up. The larval stage can last from 5 to 14 days, depending upon the temperature. Under optimum conditions, development from egg to adult takes about 7 days. 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 active only 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 from freshwater to moderate levels of salinity, alkalinity or organic pollution. Sunlit sources are preferred egg laying sites, but larvae may also be found in shaded sources. This species is generally found in ground pools but may occur in artificial containers. Some typical sources for these larvae are ditches, canals, duck club ponds, rain ponds and irrigation and tail water impoundments.

The periods of peak abundance are fall, winter and spring. This species is strongly attracted to light. In light trap collections, they are the first caught in the spring and the last in fall.

HABITS (ADULT BEHAVIOR)
Female Cs. inornata feed primarily on large domestic animals. Although humans are not bothered most of the year, active biting by this mosquito does occur in areas within the vicinity of brackish marshes during the fall and late winter months (dusk being the most common time). Adults will enter dwellings but not as frequently as some other species. 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.

Females are active fliers and can disperse 5-10 miles from their emergence site.

ECONOMIC AND MEDICAL IMPORTANCE
Cs. inornata has been found naturally infected with Western Equine Encephalitis virus (WEE) in Washington State. However, the combined factors of seasonal abundance, host feeding pattern and lack of presence in endemic areas of California makes it unlikely of being an important vector of disease.

CONTROL METHODS
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 either filling, dumping, or draining the source. Containers holding water around the home should be checked weekly or emptied or emptied (water vases, buckets, tubs, or tires).

BIOLOGICAL CONTROL
The most commonly used biological control agent in mosquito control is the mosquitofish (Gambusia affinis). Typically suitable sources for stocking mosquitofish are fishponds, watering troughs, sewage lagoons and ditches where water quality is good enough to support fish production.

CHEMICAL CONTROL
At times, it may become necessary to control populations of Cs. incidens 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.