by Wayne J. Crans, Rutgers University
(See also Morphological Comparisons of several Aedes/Ochlerotatus species)
Subgenus: Stegomyia
Type of Life Cycle: Multivoltine Aedes, Ae. triseriatus Type
Typical Habitat: Artificial Container
Larvae Present: All Season
Head Hairs:
Upper: Single
Lower : Single
Antenna:
Length: Much shorter than head
Tuft: Single, very short, inserted at middle of shaft
Abdominal Hairs (Segments III-VI): 2-2-2-1
Comb Scales: Single Row
Siphon:
Index: 2.5
Tuft: 2-3 Short, Sparse Hairs
Pecten: Evenly Spaced
Anal Segment:
Saddle: Nearly a complete ring
Precratal tufts: None
Other: Dorsal brush of anal segment consisting of 4 long single hairs (Similar to that seen in Ae. abserratus)
GEOGRAPHIC DISTRIBUTION: The Asian Tiger Mosquito, Ae. albopictus, was first detected in New Jersey at Keyport, a coastal town on Raritan Bay in Monmouth Co. A report from Florida indicated that Ae. albopictus was also present in the southern portion of the state. Further surveillance revealed that breeding populations were established in Salem and Cumberland Counties. The Keyport record is of particular interest because it represents the most northern collection site for this species on the eastern seaboard. Aedes albopictus was first collected in the United States at a tire dump near Houston, TX in 1985. The species spread rapidly through the southern United States and has been documented in 25 states over the last decade. Although isolated records of Ae. albopictus have been reported as far north as Chicago in the midwest, the mosquito has been slow to expand its range northward along the Atlantic coast. The 0° C daily mean January isotherm has been used as a conservative estimate for the northern limit of this mosquito's overwintering range in North America. Keyport, NJ is just 30 mi. South of that theoretical barrier, thus, the mosquito may be very close to the geographical limits that allow for successful overwintering in egg diapause.
Aedes albopictus spread rapidly up the eastern seaboard after its initial detection in the southern United States. The mosquito was found in Baltimore, MD in 1987 and at a site near Milford, DE during the same year. The Delaware collection site was less than 30 mi. from the tip of Cape May Co. and it seemed only a matter of time before the species would be found in New Jersey. No further northward movement, however, was detected until 1993 when Ae. albopictus eggs were recovered from an ovitrap at a military base near Harrisburg, PA. The Harrisburg site is well inland and falls slightly North of the 0° C daily mean January isotherm. Ovitrap surveillance conducted at the Pennsylvania military base the following year failed to collect additional specimens, implying that the mosquito might not have been able to overwinter successfully and establish a breeding population in the Harrisburg area. In 1994, a specimen was collected at the University of Delaware campus at Newark, DE, a location that is less than 10 mi. from the Delaware Memorial Bridge. The collections from Salem and Cumberland counties confirm that the mosquito has successfully colonized portions of southwestern New Jersey and will probably expand over much of the remaining area of our state in the next year or two.
SEASONAL DISTRIBUTION: Aedes albopictus is a multi-voltine species and should have a seasonal distribution in New Jersey similar to that of Aedes triseriatus. If this is the case, larvae should be evident in suitable breeding habitat during May or early June. If the species behaves like Ae. triseriatus, late season flooding could produce larvae into the month of October. We are not certain which strain of Ae. albopictus was introduced to the Keyport area and its ability to enter diapause is still very much in question. If the introduction came from southern Florida, the mosquito will probably not be able to survive New Jersey's winters. If the introduction is an expansion of the strain found in North Carolina, Maryland and Delaware, the mosquito may be very near its critical limit for overwintering. If the Keyport strain was imported from Asia, any number of possibilities exist regarding its ability to respond to photoperiod and survive in egg diapause. The population discovered in southern New Jersey is likely an expansion of the populations from Delaware which have been overwintering successfully for at least 8 years less than 50 miles to the south.
LARVAL HABITAT: Aedes albopictus is an opportunistic container breeder that is capable of utilizing natural as well as artificial container habitats. Although the mosquito is most often associated with discarded tires in this country, it has the ability to adapt to an exceptionally wide range of confined water sources. The mosquito is known for its ability to survive in very small collections of water, requiring only 1/4" of depth to complete its life cycle. The larval habitats of the population discovered in the Keyport area included: airplane tires, truck tires, automobile tires, a wheel barrow tire, a 50 gal. drum, plastic buckets of various sizes, a dish pan, a plastic drink cup and a crushed aluminum beverage can. The mosquito was detected during a period where New Jersey went for more than a month without any rainfall. Shortly after one brief shower at the collection site, larvae were found in the holes of a socket-set case that had been discarded at one of the local marinas.
COMMON ASSOCIATE SPECIES: In New Jersey, Ae. albopictus has been found in container habitats with: Aedes triseriatus, Aedes atropalpus, Culex pipiens & Culex restuans. More than likely, the mosquito will eventually be found breeding with each of the remaining container breeding mosquito species in New Jersey, which include: Anopheles barberi, Orthopodomyia signifera, Orthopodomyia alba& Toxorhynchites rutilus septentrionalis.
LARVAL IDENTIFICATION: Aedes albopictus larvae are relatively easy to separate from associate species collected from artificial containers. The Culex species are easily recognized and can be separated in the dipper by their longer air tubes. Aedes triseriatus larvae have a darker coloration, a characteristic serpentine motion and an elongate body shape which are useful in screening field collections but should not be relied upon for separation of early instars. Aedes atropalpus (which are becoming extremely common in tires) closely resemble Ae. albopictus in general body shape but are easily separated under the microscope by their detached pecten teeth.
There are several useful characteristics to quickly isolate the Ae. albopictus larvae from field populations of Ae. triseriatus. The air tube of Ae. albopictus has a slightly inflated appearance and is much lighter in color than that of Ae. triseriatus. The anal gills of Ae. albopictus are much longer than the saddle and are equal in size. Aedes triseriatus has much smaller gills and the ventral pair is considerably shorter than the dorsal pair. Be aware, however, that gills frequently break off in preserved specimens. As a result, gill characteristics are most useful when observing living specimens. Aedes triseriatus has a single row of comb scales that are arranged in an extremely irregular fashion. The comb scales of Ae. albopictus are set in a concise single row and are, perhaps, the most diagnostic character for a quick species check in preserved specimens. The anal saddle of Ae. albopictus is nearly complete and requires turning the preserved specimen to observe the gap.. The anal saddle of Ae. triseriatus wraps approximately 3/4 of the way around the anal segment as it does in most 4th instar Aedes that have an incomplete saddle. A particularly useful characteristic is the fact that the nearly complete saddle is found in early instar specimens of Ae. albopictus as well as late instar larvae. The lateral hairs on the saddle are useful because they can be observed in living specimens without special orientation. The lateral hairs are double in Ae. albopictus and 5-7 branched in Ae. triseriatus. The 4 long caudal hairs of the dorsal brush in Ae. albopictus are a useful characteristic because they can be discerned at very low power but should not be used as the only characteristic to separate out this species.
IMPORTANCE: It is too early to assess the true importance of the introduction of Ae. albopictus to New Jersey. The mosquito is known to be an efficient vector of dengue fever but it is extremely unlikely that dengue could ever become a public health problem in New Jersey. Preliminary findings point to Ae. albopictus as an efficient vector of eastern equine encephalitis virus (EEEV) which could become an important health issue once the mosquito becomes established on the coastal plain where EEEV is most prevalent. This mosquito could provide an important link between people and virus because of its domestic breeding habits and acceptance of avian blood meal hosts.
Aedes albopictus, has been proven to be a severe nuisance species and will certainly become an unwanted pest once it becomes firmly established in New Jersey. Some of the local residents in areas where the mosquito has been established complained of severe mosquito annoyance this summer and were able to accurately describe the characteristic markings of Ae. albopictus with considerable detail. A private citizen that read an article about the Asian Tiger Mosquito in the local newspaper decided that the mosquitoes that had been pestering her all summer were most certainly this exotic species. When she heard we were conducting a survey in the area she went into her backyard and captured a perfect adult female Ae. albopictus for us to identify. The mosquito is a pest that New Jersey mosquito control workers will have to deal with in the future.