by Wayne J. Crans, Rutgers University
Subgenus : Culex
Type of Life Cycle : Culex pipiens Type
Model for multivoltine Culex with pollution tolerance
Typical Habitat :Stagnant pools of ground water, artificial containers, catch basins, sewage seepage; tolerates water that ranges from high in organic content to grossly polluted.
Larvae Present : Spring through fall
Upper: 5-8 branched
Lower : 5-8 branched
Length: Shorter than head, constricted beyond antennal tuft
Tuft: Multiple, inserted at constriction point
Abdominal Hairs (Segments III-VI) : 2-2-2-2
Comb Scales : Patch
Tufts: Typically 4 pairs of double or triple tufts inserted beyond the pecten
Pecten: Evenly spaced on basal 1/3 of siphon
Saddle: Complete ring
Precratal tufts: None
GEOGRAPHIC DISTRIBUTION: Culex pipiens, the Northern House Mosquito, has a distribution that roughly includes the northern half of the United States. This species’ range begins just north of Maine, along the Atlantic seaboard, and extends to the state of Washington in the west with some extension into southern British Columbia. The range along the Pacific coast extends into northern California and then east on a relatively straight line to North Carolina. The species is replaced by Culex quinquefasciatus, the Southern House Mosquito, in the southern United States with limited overlap in portions of the mid-west. Culex pipiens is widespread in New Jersey and is considered common in every county of the state.
SEASONAL DISTRIBUTION: Culex pipiens provides the life cycle model for most of the domestic Culex in temperate areas. Inseminated adult females from the last generation of the season, build fat body by feeding on carbohydrates and enter hibernation in fall. The females pass the winter in diapause and do not become active during periods of warm winter weather. Hibernating females are common in basements, outbuildings and subterranean enclosures. Like Culex restuans, the females congregate near moisture and move their resting location during the winter to remain in a humid atmosphere. Mortality can be extensive during periods of winter drought. Females emerge from hibernation during May and begin depositing egg rafts in suitable habitat. Populations of this mosquito usually peak during August but breeding continues well into September. The adults from the last generation of the season lose all interest in blood meal hosts but will move in and out of overwintering sites during periods of mild fall weather. Larvae rarely persist in breeding habitats after females have entered hibernation.
LARVAL HABITAT: Culex pipiens can be found in a fairly wide range of larval habitats but are generally associated with water that has a high organic content. The species utilizes temporary ground water that ranges from mildly to grossly polluted. The species also deposits its eggs in artificial containers including tin cans, tires and any refuse that allows stagnant water to puddle. The species is decidedly urban and reaches greatest numbers in large urban centers. Catch basins and storm drains provide ideal habitat for Cx. pipiens. The species becomes particularly abundant in areas where raw sewage leaks into subterranean drainage systems. Meat packing plants and slaughter house drainage ponds support hugh populations of this species. Culex pipiens can always be collected in the effluent from sewage treatment plants.
COMMON ASSOCIATE SPECIES: Cx. restuans, Cs. inornata, An. punctipennis
LARVAL COLLECTION: No special techniques are required to collect Cx. pipiens larvae. This species is common in urban settings and can usually be found in significant numbers in a variety of habitats where stagnant water collects. Culex pipiens will oviposit readily in buckets containing prepared straw infusions. Most piles of discarded tires contain a mixture of Cx. pipiens and Cx. restuans in addition to the tire breeding Aedes.
LARVAL IDENTIFICATION: Polluted habitats do not generally support a very wide variety of species. Most larval samples from polluted water sources consist mainly of Cx. pipiens and Cx restuans. Culex pipiens larvae are easily distinguished from Cx. restuans by the length and shape of the antennae. The characteristic antennal shape is difficult to see in the dipper but the slightly longer, constricted antennae and prominent antennal tufts can be discerned with practice. The multiple hair tufts on the siphon can be used as a diagnostic character under the microscope. Culex salinarius is a closely related species that is easily distinguished by the longer, more slender siphon.
REPRESENTATIVE COLLECTION RECORDS
Northern New Jersey
Location: Parsippany, Morris Co.
Date: July 12
Habitat: Sewage Effluent
Instar: 1st - 4th & Pupae
Southern New Jersey
Location: Cape May Court House, Cape May Co.
Date: August 3
Habitat : Catch Basin
Instar: : 1st - 4th & Pupae
IMPORTANCE: Culex pipiens occurs in 2 behavioral forms that cannot easily be distinguished morphologically. The true “pipiens” form is primarily a bird feeder and does not appear to be a major biting pest. The “molestus” form is autogenous for its first batch of eggs but reverts to blood feeding to produce additional egg batches. The “molestus” form readily accepts blood from mammalian hosts, including humans. Urban Culex pipiens tend to be biting pests while rural Culex pipiens seem to be bird feeders. It is not clear whether the behavioral differences represent “pipiens” vs. “molestus” in all cases. It has also been suggested that many of the biting populations from urban areas may be Culex restuans, a species that can easily be confused with Cx. pipiens in the adult stage. Culex pipiens is recognized as the primary vector of St. Louis encephalitis in the northern United States. Sizeable outbreaks of this disease take place in urban settings with peridomestic birds functioning as the primary urban reservoirs. It is not clear whether the “pipiens” form or the “molestus” form poses the greatest risk to human health. Either form could be responsible for the transfer of virus from bird to human.