Culex pipiens pipiens and Culex pipiens quinquefasciatus are so similar that they will be treated here as one. They are commonly referred to as “house” mosquitoes because of their often-close relationship with humans and their habit of entering into houses and sometimes even breeding in containers indoors.
Cx. pipiens is a light brown, medium sized mosquito with a blunt-tipped abdomen. There are narrow white bands on the abdominal segments but none on the legs or proboscis (beak). Males resemble females except they have bushy antennae and long palpi on their head and “claspers” on the tip of their abdomen.
This is the most widely distributed mosquito species in the World. They are also widespread throughout the U.S. and California.
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, somewhat polluted water such as sewage, street drainage, septic tanks and cesspools, industrial wastes, and such backyard sources as unused swimming pools, fouled ornamental ponds, cooler drainwater 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. pipiens readily bite humans, but birds and other mammals are considered the primary hosts. This species bites under low light intensity or in the dark, tending to seek entry into homes and resting in darkened areas when the light is bright. Children and babies are most susceptible, often covered with numbers of reddened marks for many days following the biting period. To adults, their humming at night is an added irritant to the bite and sleepless night.
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.
Small populations of these mosquitoes tend to remain in a localized area (a block or two), which is more common. Large populations (as from oxidation ponds) may move 3-5 miles seeking a host.
ECONOMIC AND MEDICAL IMPORTANCE
Cx. pipiens is primarily a domestic nuisance, by may affect industrial and agricultural production in certain situations.
This species is considered a secondary vector of Western Equine Encephalitis (WEE) and St. Louis Encephalitis (SLE) viruses in California. They were found to be infected with West Nile virus in southern California during 2004 and are considered important vectors.
The organisms that cause bird malaria, fowl pox and heartworm of dogs can also be transmitted by house mosquitoes.
PREVENTION AND CORRECTION
Where possible, the best approach is to prevent mosquitoes from breeding by eliminating or modifying breeding sites. This may be accomplished by such actions as filing, dumping, ditching, or otherwise draining the source. Often this is not feasible with sources such as septic tanks, cesspools and rainwater barrels. These types of sources should be tightly covered or screened to prevent mosquitoes from gaining access to the area to lay eggs. Temporary containers around the home should be checked weekly to remove standing water as in buckets, flower vases, tubs, or even tires. Underground drains or cleanouts should also be checked. Check for broken or leaking pipes under the house.
The most commonly used biological control agent in mosquito control is the mosquitofish (Gambusia affinis). The stocking of mosquitofish is often an effective control measure in 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.
At times, it may become necessary to control populations of Cs. pipiens 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.