Culiseta morsitans

Culiseta morsitans is a species of mosquito in the family Culicidae, widely distributed in temperate regions of North America and Eurasia. It is univoltine, producing one generation per year, with a life cycle adapted to colder climates. This species is recognized as a secondary vector for the Eastern equine encephalitis virus (EEEV), primarily affecting birds but occasionally transmitting the virus to humans and horses.^[1]

Culiseta morsitans
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Diptera
Family:	Culicidae
Genus:	Culiseta
Species:	C. morsitans
Binomial name
Culiseta morsitans Theobald, 1901

Description

The larvae of Culiseta morsitans are identifiable by distinct morphological traits: upper head hairs have 4–6 branches, while lower head hairs are double and notably long. The antenna matches the head's length, is curved, and features a tuft of hairs on its outer quarter extending beyond the tip. The siphon, a respiratory structure, has an index (length-to-width ratio) of 6.0–7.0, with a tuft of 4–5 large hairs near its base within the pecten.^[2] Adult mosquitoes are characterized by an entirely dark tarsomere 4 on the hindleg—distinguishing them from related species like Culiseta fumipennis—and palpi with scattered pale scales, mostly at the apex. The scutum (dorsal thorax) lacks prominent patterns, and prespiracular setae are present while postspiracular setae are absent.^[2]

Life cycle

Culiseta morsitans is univoltine, completing one generation annually. Females lay an average of 109 eggs in rafts on damp soil or leaf litter, a less common trait among mosquitoes, and these eggs overwinter, remaining viable for months under high humidity.^[3] Larvae hatch in early spring, typically by mid-April, and develop slowly in cold water habitats.^[4] Pupation occurs by late April to early May, with adults emerging in early May and remaining active until September or October.^[5] Females are long-lived, often appearing in light trap collections well into summer.^[3]

Distribution

Culiseta morsitans has a Holarctic distribution. In North America, it is common in the northern United States, including New England, upper New York State, and as far south as Delaware. It extends across Canada, from Alberta, British Columbia, Manitoba, and Nova Scotia to the Yukon Territory and Alaska.^[5][6] In Eurasia, it ranges from Northern and Central Europe to Siberia, becoming less frequent in southern regions, where it may be replaced by Culiseta litorea.^[7] Its prevalence in colder climates reflects its cold-adapted biology.

Habitat

This species breeds in semi-permanent woodland swamps, shallow cattail swamps, and root mats in acidic water, often in densely wooded areas with sedge grasses (Carex) or mosses.^[2] Larvae thrive in fresh or slightly brackish waters rich in detritus, including temporary pools, peat bogs, and undercut root systems.^[4] Adults are woodland-dwellers with a limited flight range, typically resting in shaded areas near breeding sites.^[5]

Ecology

Culiseta morsitans primarily feeds on birds, contributing to the enzootic cycle of Eastern equine encephalitis virus, with 94.2% of blood meals from avian hosts, 0.8% from mammals, and 5.0% mixed.^[1] Larvae feed on organic detritus in water, supporting their role as decomposers in wetland ecosystems.^[2] The species is an indicator of wetland health, and its presence is tied to specific environmental conditions like acidic, detritus-rich waters.^[7]

Medical importance

Adult females are blood-feeders, predominantly targeting avian hosts but occasionally biting mammals, including humans.^[1] Culiseta morsitans is a secondary vector for Eastern equine encephalitis virus, a severe arbovirus affecting birds, horses, and humans. It has been detected with Eastern equine encephalitis virus in surveillance programs, notably in New York from 1993–2012.^[8] Its potential to overwinter Eastern equine encephalitis virus in eggs adds to its epidemiological significance, though this requires further study.^[2]