Aedes grossbecki Dyar and Knab

by Wayne J. Crans, Rutgers University


Subgenus: Ochlerotatus

Type of Life Cycle: Univoltine Northern Aedes

Typical Habitat: Flooded Woodlands

Larvae Present: Early Spring

Head Hairs:

Upper: Triple (Occasionally 2 or 4 branched)

Lower : Double (Occasionally triple)

Antenna:

Length: Nearly half as long as head

Tuft: Inserted at middle of shaft

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

Comb Scales : Patch

Siphon:

Index: 3.5

Tuft: Large, multiple

Pecten: Evenly spaced

Anal Segment:

Saddle: Incomplete

Precratal tufts: 3-5

Other : Spiculated saddle

GEOGRAPHIC DISTRIBUTION: Aedes grossbecki is recognized as a mosquito of the southeastern United States, but the species is fairly well distributed in New Jersey. The mosquito occurs at low levels throughout the more southern counties of the state during the early Spring and larvae have been collected as far north as Morris County. Collection records from New York State show that the distribution of this species extends beyond the New Jersey border. In all probability, Ae. grossbecki exists at very low levels in all but the most northern counties of New Jersey.

SEASONAL DISTRIBUTION: Aedes grossbecki is one of the earliest mosquitoes to hatch from overwintering eggs. Development is rapid, considering the cold water that is present in the early Spring. In southern New Jersey, the larvae reach 3rd instar during the middle of March and pupate during the 1st or 2nd week of April. In the northern range of its distribution, the larvae hatch with Aedes excrucians where both species reach 3rd instar in early April and pupate during the 3rd week of the month. Aedes grossbecki is on the wing before most mosquito control agencies put out their light traps, however, the species persists until early summer and is usually represented in low numbers in trap collections during May and June.

LARVAL HABITAT: The larvae of Ae. grossbecki are most common in flooded woodlands where mature Red Maple, Sweet Gum Oak and Beech are the dominant trees. In southern New Jersey, Holly replaces Beech as an indicator and the larvae frequently occur in borrow pits where sand has been extracted for land fill. Cat Briar is a common plant at both latitudes. Decomposing leaves add tannins to the aquatic habitat and in most cases, habitat water is so dark that a white dipper submerged more than 2 ft below the surface cannot be clearly detected.

COMMON ASSOCIATE SPECIES: Ae. canadensis, Ae. sticticus, Ae. excrucians

LARVAL COLLECTION: Aedes grossbecki larvae are easy to locate in southern New Jersey where the only associate species in flooded woodlands are Aedes canadensis and Aedes sticticus. The Ae. grossbecki larvae are rarely numerous but stand out because of their larger size. Placing the dipper below the surface of the pool provides a white background to selectively capture the larger specimens. The obvious size difference provides near 100% accuracy in the selective collection of this species. In the more northern latitudes, Ae. grossbecki may be mixed with Ae. excrucians, a larva of similar size. Selective collection requires cursory examination of siphon length, a process that can demand considerable effort under field conditions. If the specimens are brought back to the laboratory and placed into a shallow pan, the species can easily be separated on the basis of behavior. Ae. excrucians larvae lie flat on the bottom when they are resting below the surface. Aedes grossbecki larvae stand on their heads with the air tube pointing straight up.

LARVAL IDENTIFICATION: The larvae of Ae. grossbecki can be confirmed in living specimens with minimal difficulty. The head hair formula of Upper (3) and Lower (2) is relatively constant and unlike other larvae collected during the early season. Both Ae. canadensis and Ae. sticticus possess multiple upper head hairs and do not approach the size of the larger Ae. grossbecki at this time of year. Confirmation of the identification can be made by examining the posterior margin of the saddle. Aedes grossbecki has a spiculate saddle and small teeth are quite apparent along the margin if the specimen is placed against a white background with the siphon directed nearly upright. The small teeth give the margin of the saddle a saw-toothed effect. The head hair formula and spiculated saddle separate Ae. grossbecki from all but aberrant Aedes stimulans, a species that could conceivably overlap Ae. grossbecki in the northernmost portion of its range.

REPRESENTATIVE COLLECTION RECORDS:

Northern New Jersey

Location: South Brunswick, Middlesex Co.

Date : April 8

Habitat : Flooded Woodland near intersection of

Broadway and Friendship off Rt. 130 South

Instar : Early 3rd

Southern New Jersey

Location: Villas, Cape May Co.

Date : April 7

Habitat : Deep Borrow Pit

Instar : 4th

IMPORTANCE: Aedes grossbecki has been described as a persistent biter but the species rarely occurs in high enough numbers to be considered a nuisance. Its spotty distribution in the state and early spring activity period render the mosquito as a minor pest species in New Jersey.

 


Center for Vector Biology