Aedes atropalpus (Coquillett)
by Wayne J. Crans, Rutgers University
(See also Morphological Comparisons of several Aedes/Ochlerotatus species)
Type of Life Cycle: Multivoltine Aedes
Typical Habitat: Discarded Tires in New Jersey, Rockpools in other geographic areas
Larvae Present: Early spring through fall
Lower : Single
Length: About 1/2 as long as head
Tuft: Double or triple, small, inserted near middle of shaft
Abdominal Hairs (Segments III-VI): 3-3-3-2
Comb Scales: Patch
Tuft: Multiple, inserted well within pecten
Pecten: Extending nearly to tip of siphon, last 2-4 teeth detached
Precratal tufts: None
Other: Gills long and pointed
GEOGRAPHIC DISTRIBUTION: Aedes atropalpus is found from Labrador south to the Florida border along the eastern seaboard of the United States. Its distribution extends west to Minnesota in the northern part of its range and westward through Tennessee and Mississippi in the south. Aedes atropalpus is commonly referred to as the rockpool mosquito because of its association with water filled depressions in shear rock. Larval populations have been reported from rockholes that form in outcroppings along the North Atlantic seacoast and in rockholes found along mountain streams in more inland areas. John B. Smith added Ae. atropalpus to New Jersey's checklist on the basis of adults collected in light traps. He predicted that larvae would eventually be found in typical habitat along the Delaware River in northwestern New Jersey but was never able to confirm his hypothesis. The larvae of Ae. atropalpus were not detected in New Jersey until 1986 when a breeding population was discovered in a tire pile in Warren County. Once the mosquito was known to breed in tires, larvae have been discovered a number of counties from Cape May in the south to Essex in the north Aedes atropalpus appears to be far more common in tires than in the typical habitat described for this species. Like Aedes albopictus, this mosquito has probably been spread via tires that are moved about for re-capping purposes. It is quite possible that the mosquito is now established in every county of New Jersey.
SEASONAL DISTRIBUTION: Aedes atropalpus is a multivoltine Aedes with a life cycle that resembles Aedes triseriatus in terms of larval habitat and overwintering mechanisms. The species overwinters in the egg stage but initiates its season earlier than other container breeding Aedes at our latitude. The eggs of the overwintering generation are deposited on the sides of the habitat and rely on rising water levels in spring to trigger hatch. In subsequent generations, the eggs are usually laid directly on the water's surface. Egg hatch begins in April and larvae are evident in suitable habitat well into the fall. In early spring, Ae. atropalpus larvae are mixed with Culex restuans, well before Ae. triseriatus larvae are evident. In the fall, Ae. atropalpus larvae can be collected as late as November.
LARVAL HABITAT: Most available literature on habitat preference indicates that Ae. atropalpus is most often associated with the rockpool habitats that coined its common name. The mosquito is known to breed in artificial containers but containers are normally listed as an atypical habitat. In New Jersey, the mosquito has never been found in rockpool habitats and many have looked. Its abundance in tires in so many different areas of the state suggests that New Jersey's strain has become well adapted to container habitats. The detection of Aedes albopictus in Monmouth County in 1995 resulted in widespread surveillance of container habitats in that area. Aedes atropalpus was found to be extremely common in a variety of artificial containers. Tires, however were most common and the species was found in discarded tires in open sunlight, tires that were awaiting re-capping at a commercial facility and tires that were displayed on racks for sale at gas stations. The only unique habitat where we found the species was in standing water that collected in boats stored in dry dock at local marinas. Available evidence strongly suggests that this mosquito is a container breeder in New Jersey that is rarely, if ever, found in the rockpool habitats described for the species.
COMMON ASSOCIATE SPECIES: Ae. triseriatus, Cx. restuans, Cx. pipiens, Ae. albopictus
LARVAL COLLECTION: Aedes atropalpus larvae occur in fairly large numbers in the tire habitats we have sampled and should pose no problem in terms of collection. The mosquito rarely is found in pure culture, however, which requires techniques to separate them from the more common species found in containers. We prefer using a soup ladle and white enamel pan. The ladle is small enough to remove water from the tire without rubbing against the sides and the white pan provides a clear background to discern gross larval characteristics. A tea strainer can be used in place of a dipper in tires that have a minimum of leaf litter and organic debris. Culex can be separated from mixed populations against the white background of the pan by their longer air tubes and prominent antennae. Aedes triseriatus can be separated by their characteristic undulating swimming motion, gray color and more elongate body shape. Aedes atropalpus, looks very much like Ae. albopictus, however, and we have not been able to satisfactorily separate these two species in the field.
LARVAL IDENTIFICATION: Aedes atropalpus larvae are easy to recognize under the microscope and accurate identification is possible even with living specimens at moderate magnification. This is the only mosquito with detached pecten teeth that breeds in containers at our latitude. Moreover, the pecten extend nearly to the tip of the siphon in this species and the siphonal tuft is inserted at the midpoint, well within the row of teeth. The comb scales of Ae. atropalpus are arranged in a patch in direct contrast to the single row found in other container breeding Aedes. As a result, the terminal segments provide a quick, accurate method of separating this mosquito from both Ae. triseriatus and Ae. albopictus. The long, pointed gills provide another diagnostic character that can be useful to help separate living specimens under the microscope. The gills in Aedes triseriatus are much shorter those of Ae. atropalpus and the paired gills of the treehole mosquito are of unequal length. Ae. albopictus has large, trailing globulate gills that are considerably thicker and rounded, rather than pointed, at the base.
REPRESENTATIVE COLLECTION RECORDS
Northern New Jersey
Location: Bellevidere, Warren Co.
Date : May 3
Habitat : Discarded Tires
Instar : 3rd & 4th
Central New Jersey
Location: Keyport, Monmouth Co.
Date :August 8
Habitat : Bucket, Tire, Hull of water filled boat
Instar : 1st - 4th & Pupae
Southern New Jersey
Location: Goshen, Cape May Co.
Date :August 17
Habitat : Discarded Tires
Instar : 1st - 2nd
IMPORTANCE: Aedes atropalpus is a mosquito that has been described as a persistent biter in areas close to its larval habitat. The New Jersey strain we colonized from Keyport is autogenous and there is strong evidence to suggest that there is a high incidence of autogeny in the wild. Because of its low abundance, limited flight range and It is doubtful that this mosquito has any real economic importance in New Jersey.