Aedes thibaulti Dyar & Knab

Aedes thibaulti Dyar & Knab

by Wayne J. Crans, Rutgers University


Subgenus: Ochlerotatus

Type of Life Cycle: Univoltine, Northern Aedes

Typical Habitat: Dark recesses under up-rooted trees

Larvae Present: Very Early Spring

Head Hairs:

Upper: Multiple (5-8 Branches), Large

Lower: Multiple (6 Branches), Large

Antenna:

Length: Nearly as long as head, slender

Tuft: Inserted near middle of shaft

Abdominal Hairs (Segments III-VI): 2-2-2-2

Comb Scales: Patch

Siphon:

Index: 4.5-5.0

Tuft: 4-8 Hairs

Pecten: Evenly spaced

Anal Segment:

Saddle: Incomplete

Precratal tufts: 2-3

Other: Saddle spiculate

GEOGRAPHIC DISTRIBUTIONAe. thibaulti is a mosquito with a very spotty geographic distribution. Most records come from the southern portion of the United States, but isolated collections have been reported as far north as Ontario, Canada. The restricted larval habitat may limit distribution within its range and the secretive larval behavior exhibited by this species undoubtedly minimizes collection in areas where it does occur. The species was not detected in New Jersey until 1983 when Jim McNelly found larvae in the southern portion of Cape May County. Since that time, adults have been identified from light trap collections in Burlington and Gloucester counties and larvae have been located in Burlington and Atlantic counties. In all probability, the species will eventually be detected in some of the more northern counties of New Jersey where suitable larval habitat is present.

SEASONAL DISTRIBUTION: Aedes thibaulti is an exceptionally early season mosquito species and fourth instar larvae can frequently be collected as early as the 3rd week of March. Larval instars are mixed during the early season, however, and in some years specimens can be taken from suitable habitat into the month of May. During the earliest portion of the season, Ae. thibaulti appears to be the only species present within the crypts that characteristically hold larvae. As the season advances, Cs. melanura becomes an associate species. In some areas, Ae. canadensis becomes common in the surrounding swamp habitat and occasional specimens sometimes enter the recesses where Ae. thibaulti are found.

LARVAL HABITAT: The larvae of Ae. thibaulti are nearly subterranean in their distribution and congregate in crypts that have little exposure to light. Collections in New Jersey have been most common from dark recesses provided by uprooted trees. The type habitat located by McNelly in New Jersey, was a deeply flooded woodland where numerous mature red maple trees had become uprooted. Erosion had cut a deep recess into the root mat and water from the surrounding swamp filled the cavity created by the fallen tree. Secondary growth had become established on the soil covering the undercut portion, creating a high dome over the larval habitat. Erosion through the dome created several holes large enough to admit a dipper. The water level was several feet below the opening and larvae were detected, in large numbers, in the darkest portions of the habitat. Collections have since been made from a number of similar situations involving uprooted trees in maple swamp habitats. Large cavities appear to hold the greatest numbers of larvae but specimens can be collected from smaller recesses in areas where large breeding populations occur.

COMMON ASSOCIATE SPECIES: Cs. melanuraAe. canadensis

LARVAL COLLECTION: The larvae of Ae. thibaulti congregate in the darkest portions of their subterranean habitat. If an access hole can be found from above, the recesses can be dipped without causing undue disturbance of the water. Larvae tend to remain close to the sides of the root mat, thus, the dipper should be placed as close to the wall of the habitat as possible. If no access hole is available from above, it is possible to wade into the cavity and reach as far back as possible before taking the dip. Wading, however, causes the larvae to sound and striking the roof or sides of the cavity creates further disturbance.Ae. thibaulti is a species that must be collected with slow, deliberate sampling of suspected habitat. Finding the larvae in a new area is the hardest part of the task. Once the species is located, collection is relatively simple.

LARVAL IDENTIFICATION: The larvae of Ae. thibaulti are quite striking and can usually be tentatively identified in the dipper. The species has a relatively long air tube and the abdomen looks as though someone had outlined the individual segments with a very fine dark pen. Most mosquito larvae are brown in color but this species has a definite gray tone. The darkened bands that appear on the abdomen further accentuate the gray coloration. The color exhibited by Ae. thibaulti larvae resembles that of Ae. triseriatus, another species that appears gray in color when first taken from the larval habitat. Under the microscope, the species has densely multiple head hairs and a longer than normal siphon for most Aedes. If the saddle is viewed against a white background with the air tube pointing nearly straight up, the spicules along the posterior margin of the spiculated saddle stand out like little teeth.

REPRESENTATIVE COLLECTION RECORDS

Northern New Jersey

None Collected

Southern New Jersey

Location: Villas, Cape May Co.

Date: April 7

Habitat: Red Maple Swamp

Under covered root mat of fallen tree

Instar: 2nd - 4th

Southern New Jersey

Location: Estelle Manor, Atlantic Co.

Date: April 1

Habitat: Recess of fallen tree

Instar: All instars

IMPORTANCE: Aedes thibaulti is thought to be a mammalian feeding mosquito but nothing is known of its blood meal preference range in southern New Jersey. Its spotty distribution and restricted larval habitat make the species extremely rare in our state. As a result, Ae. thibaulti has no known pest significance or medical importance and, at this time, merely represents an interesting scientific curiosity among New Jersey's mosquito fauna.

 

 


Center for Vector Biology