Aedes vexans (Meigen) 

by Wayne J. Crans, Rutgers University

Subgenus: Aedimorphus
Type of Life Cycle : Model for Aedes vexansType
Multivoltine Aedes/Psorophora
Typical Habitat : Temporary Rainpools in open areas
Larvae Present : Late Spring through Fall following heavy rains
Head Hairs Upper: 3-5 branched  Lower: 2-3 branched
AntennaLength: Half as long as head Tuft: Inserted near middle of shaft
Abdominal Hairs (Segments III-VI) : Variable
Comb Scales : Irregular Single or Double Row
SiphonIndex  : 3.0 – 3.5 Tuft   : 3-6 branched, smallPecten : To middle or beyond, 1-3 Teeth Detached
Anal SegmentSaddle : Incomplete, extends well down the sides
Precratal tufts : 4 - 5 

GEOGRAPHIC DISTRIBUTION: Aedes vexans is found in every state in the United States including Alaska and Hawaii. The species has a distribution in the continental USA that extends from southern Florida to Quebec, on the east coast, and from southern California to Alaska in the west.  In Canada, the species is missing only from Newfoundland, Labrador and portions of the Northwest Territory.  Aedes vexans is on the checklist of every county in New Jersey and is considered common in every portion of the state. 

SEASONAL DISTRIBUTION: Aedes vexans larvae hatch from overwintering eggs during spring, appearing shortly after water temperatures reach 70^o F.  In the southern half of the state, larvae may appear in May.  In more northern areas, Ae. vexans may not be evident until June.  Seasonal distribution depends upon rainfall patterns as is typical with multivoltine species that depend upon rain to restore their breeding habitat.  Fall broods extend well into September and late season broods can be sizeable, particularly when hurricanes deposit extensive floodwater. 

LARVAL HABITAT: Virtually any transient water can support Ae. vexans larvae, but rainpools in unshaded areas produce the largest broods.  The species is most common in grassy pools that border wooded areas but specimens can be encountered in partially shaded woodland pools, roadside ditches, and vernal pools in open fields.  Dredge spoil holding areas along the Delaware River can produce tremendous broods when dredging operations flood sites that have dried down and fissured.  The cracked soil provides ideal oviposition substrate for this species and extensive dredging operations usually produce notable broods  During the early portion of its breeding season, the species is frequently mixed with Ae. canadensis, Ae. sticticus and Ae. cinereus.  During most of the summer, the species can share habitat with Ae. trivittatus, in the north, Ae. atlanticus, in the south, and Ps. columbiae and Ps. ferox throughout its range.  Ae. vexans is preyed upon by Ps. ciliata in open pools and Ps. howardii in areas where foliage provides shade.  Near the coast, the species occasionally is found with Ae. cantator in slightly brackish water along the edge of saltmarsh habitat.  Aedes vexans has a propensity to disperse and can cause nuisance far from its breeding habitat.

COMMON ASSOCIATE SPECIES: Ps. columbiae, Ps. ferox, Ae. cinereus, Ae. atlanticus, Ae. canadensis 

LARVAL COLLECTION: Aedes vexans larvae are so numerous in their habitat that no special collection techniques are needed to locate the species.  In most cases, floodwater habitats will be dominated by this abundant mid-season mosquito.  Rare floodwater species are frequently overlooked because of the repeated occurrence of this mosquito over a wide range of habitats after summer rains.  It pays to collect large numbers of larvae from typical habitat and place them in a white pan at the field site for sorting purposes.  Larvae that appear atypical because of size, color or behavior should be placed in separate vials for closer examination in the laboratory.  

LARVAL IDENTIFICATION: Aedes vexans larvae are relatively easy to identify by the combination of separated pecten teeth, exceptionally small siphonal tuft, nearly complete saddle and characteristic comb scales.  The only species it might be confused with is Ae. cinereus, a species that shares many of the same larval characters. Most keys separate Ae. cinereus by the orientation of head hairs, with upper, lower and preantennal aligned in an even row.  The head hairs on Ae. vexans do not line up, and the character is useful for cursory screening purposes.  Most mis-identifications of this species is the result of keying out specimens that have not reached the 4^th instar.  Third instar Ae. vexans key out as Ae. riparius in some keys, due primarily to early instar variation in head hair and saddle characteristics. 

REPRESENTATIVE COLLECTION RECORDS:
Northern New Jersey
Location: Wantage, Sussex Co.
Date:  July 20
Habitat: Airport Floodwater
Instar: 3rd & 4th 

Southern New Jersey
Location: Chatsworth, Burlington Co.
Date:  August 12
Habitat: Tire ruts in open grass
Instar: 3rd & 4th 

IMPORTANCE: Aedes vexans is recognized as New Jersey’s most serious pest mosquito due to its abundance, widespread distribution and breeding potential in floodwater habitats.  The mosquito probably does not reach the nuisance levels of Aedes sollicitans in coastal areas but causes annoyance over a much broader range of the state.   The mosquito has not definitely been documented as a vector of disease but has been implicated as a secondary vector of eastern equine encephalitis and dog heartworm.