Culiseta morsitans (Theobald)

by Wayne J. Crans, Rutgers University

Subgenus: Culicella

Type of Life Cycle: Univoltine Northern Aedes

Typical Habitat: Semi-permanent woodland swamps containing tussocks of sedge grasses

Larvae Present: Early Spring

Head Hairs:

Upper: 4-6

Lower : Double, very long

Antenna:

Length: As long as head, distinctly curved

Tuft: Inserted on outer 1/4 of shaft, extending well beyond tip

Abdominal Hairs (Segments III-VI): 1-1-1-1

Comb Scales: Large patch

Siphon:

Index: 6.0 - 7.0

Tuft: 4-5 Hairs, Large, inserted within pecten near base of siphon

Pecten: At base of siphon with 1-2 teeth detached

Anal Segment:

Saddle: Complete ring

Precratal tufts: 6-7, piercing the saddle

Other : Anal segment exceptionally long

GEOGRAPHIC DISTRIBUTION: Culiseta morsitans is a mosquito of the northern United States with a distribution that extends through Canadian Yukon Territory into Alaska. The mosquito is fairly common in New England and upper New York state. Records from the Atlantic coast region indicate that the species has been collected as far south as Delaware. Collection records from New Jersey indicate that the species is relatively common in the northern 1/3 of the state with localized concentrations in some areas of Sussex, Passaic, Bergen, Warren and Morris counties. Collections from the southern 2/3 of the state are sparse and little is known of its distribution and behavior in the Pine Barrens region or on the inner coastal plain.

SEASONAL DISTRIBUTION: Culiseta morsitans has a life cycle similar to that of the northern Aedes group of mosquitoes. The species is considered univoltine but females are long lived and frequently appear in light trap collections well into the summer. Unlike most members of the Genus Culiseta, the egg rafts are deposited on damp earth, probably deep within the Carex tussocks that are so common in their breeding habitat. The species overwinters in the egg stage and early instar Cs. morsitans larvae can usually be collected by the 2nd or 3rd week of April. Development is relatively slow in the cold water habitats where the species is most common and egg hatch extends over a period of many weeks. Pupae usually appear by late April but some larvae remain in the habitat until late-May. Adults have been collected as late as October, suggesting that the species may have a late season generation similar to that seen in Aedes canadensis and Aedes cinereus. Studies from other parts of the country suggest that females on the wing in fall are remnants of the spring hatch. To date, no larval information has been gathered to document a late summer generation.

LARVAL HABITAT: Culiseta morsitans has been collected from a variety of early season bog habitats but is most common in semi- permanent swamps in densely wooded areas. Mature stands of red maple that grow in 12-18" of early spring ground water provide typical habitat in northern New Jersey. Uprooted trees are common in many of the swamps that support this species and tussocks of Carex serve as indicators of the semi-permanent nature of the habitat. Culiseta morsitans is less common in more open swampland, but collections have been made from shallow cat tail swamps, particularly those with dense patches of emergent grasses and a very soft substrate. In the extreme northern portions of Sussex Co., Cs. morsitans has also been collected from deep cavities in the root mats of fallen trees, in acid water situations together with Culiseta melanura larvae.

COMMON ASSOCIATE SPECIES: Ae. cinereus, Ae. fitchii, An. walkeri, Cx. territans, Cs. melanura

LARVAL COLLECTION: Culiseta morsitans larvae congregate in dense vegetation during most of their developmental period. Carex appears to be an indicator plant and fairly large numbers of larvae can be collected by placing the dipper close to a Carex tussock and drawing the water from the dead blades surrounding the plant. The larvae can also be found among the grasses and mosses that grow on the root mats of the younger trees in the swamp. Placing the dipper close to an undercut root system will frequently collect larvae. Dipping in the deepest recesses of any of the trees that have been uprooted can also be productive. Culiseta morsitans larvae appear to remain close to stands of aquatic vegetation and have a tendency to gather in the darker portions of the habitat. Dipping should be restricted to edge zones within the habitat because this species will rarely be found in any of the open water within the swamp.

LARVAL IDENTIFICATION: Culiseta morsitans larvae occur with a variety of associate species that possess long air tubes and prominent antennae. As a result, identification of specimens in the dipper is difficult with this species and microscopic examination of collections from suspected habitats is essential. It is relatively easy to recognize this mosquito as a member of the Genus Culiseta under the microscope because of the large, basal tufts on the siphon. Workers that are used to examining Culiseta melanura for basal tufts will find the enlarged tufts of this species a refreshing change of pace. The species also possesses a long, thin air tube that is devoid of the smaller tufts that are found in Cs. melanura and most Culex species. Culiseta morsitans, however, closely resembles Culiseta minnesotae and care must be taken to confirm which species has actually been collected. The later species is normally separated on the basis of 7 or more branches in the upper head hairs, but the characters do overlap and some specimens should be reared to the adult stage for confirmation.

REPRESENTATIVE COLLECTION RECORDS

Northern New Jersey

Location: Byram, Sussex Co.

Date : April 21

Habitat : Semi-permanent Swamps

Off Rt. 206 near Cranberry Lake

Instar : 2rd & 3rd

Northern New Jersey

Location: High Point State Forest

Date : May 17

Habitat : Beaver Swamps

Numerous locations along Saw Mill Road

Instar : 4th & Pupae

IMPORTANCE: Culiseta morsitans is a woodland species with a limited flight range. The species is primarily an avian feeder and has little or no affinity for humans. The species may function as a secondary vector of eastern equine encephalitis virus (EEEV) in some parts of its range. The overwintering egg stage has been suggested as a possible overwintering mechanism for EEEV but no field data have been gathered to support that hypothesis.

This webpage was begun on 7 July 1996 and last updated on 1 June 2010