Asian Tiger Mosquito

The Asian Tiger Mosquito (Aedes albopictus) is one of the most widespread and medically significant mosquito species in the world. Recognised by its distinctive black-and-white striped body and legs, it is an aggressive daytime biter and an efficient vector of several arboviral diseases, including dengue fever, chikungunya, and Zika virus. Originally native to the tropical and subtropical forests of Southeast Asia, the species has spread globally over the past few decades, largely through human activities such as international trade and travel. Its adaptability to urban environments and temperate climates has made it one of the most invasive mosquito species worldwide.

Taxonomy and Classification

The Asian Tiger Mosquito belongs to the genus Aedes, family Culicidae, order Diptera, and class Insecta. Its scientific classification is as follows:

• Kingdom: Animalia
• Phylum: Arthropoda
• Class: Insecta
• Order: Diptera
• Family: Culicidae
• Genus: Aedes
• Species: Aedes albopictus (Skuse, 1894)

It is closely related to Aedes aegypti (the Yellow Fever Mosquito), but differs in its ecology, climatic tolerance, and geographical spread.

Physical Characteristics

The Asian Tiger Mosquito is easily identifiable due to its striking appearance.

• Colouration: Shiny black body with distinct white bands on the legs and a single white stripe running down the centre of the thorax.
• Size: Small to medium-sized, about 2 to 10 millimetres in length.
• Proboscis: Long, needle-like, adapted for piercing skin and sucking blood.
• Wings: Narrow, with fine scales and no white markings.
• Resting posture: The body is held parallel to the surface, with hind legs lifted slightly, typical of Aedes mosquitoes.

These visual traits have earned it the name “Tiger Mosquito” due to its striped, tiger-like appearance.

Habitat and Breeding Behaviour

The Asian Tiger Mosquito is highly adaptable, breeding in a wide variety of natural and artificial water containers. Unlike some other mosquitoes that prefer polluted or large water bodies, Aedes albopictus breeds primarily in small, clean, stagnant water sources such as:

• Tree holes and bamboo stumps
• Flower pots, buckets, tyres, and discarded containers
• Overhead tanks, gutters, and coconut shells
• Water accumulated in leaf axils or rock crevices

The species is strongly synanthropic—it thrives in close association with human settlements—and is most active during early morning and late afternoon.
Female mosquitoes lay eggs on damp surfaces just above the waterline. These eggs are remarkably resistant to drying and can survive for months in dry conditions, hatching when re-immersed in water.

Life Cycle

The life cycle of Aedes albopictus comprises four distinct stages—egg, larva, pupa, and adult—which can be completed within 7–10 days under favourable conditions.

1. Egg Stage: Females lay eggs singly on moist surfaces near water. These eggs can withstand desiccation, allowing the species to survive dry seasons.
2. Larval Stage: The larvae, known as wrigglers, live in water and feed on organic matter and microorganisms. They undergo four moults over 4–5 days.
3. Pupal Stage: The pupae (tumblers) are aquatic and mobile but do not feed. They metamorphose into adults within 1–2 days.
4. Adult Stage: Adults emerge, dry their wings, and become capable of flight within hours. Females typically live for 2–4 weeks and require blood meals for egg development, while males feed exclusively on nectar.

Geographic Distribution and Global Spread

Originally restricted to Southeast Asia, Aedes albopictus has now spread to all continents except Antarctica. Its expansion began in the late 20th century, primarily through the global trade of used tyres and ornamental plants, which provide ideal breeding habitats.
Major regions where the Asian Tiger Mosquito is now established include:

• Asia: India, China, Japan, Indonesia, Thailand, and Sri Lanka
• Europe: Italy, France, Spain, Greece, Germany, and parts of Eastern Europe
• Americas: United States, Brazil, Mexico, Argentina, and the Caribbean islands
• Africa: Coastal and equatorial regions
• Oceania: Pacific islands and parts of Australia

Its ability to tolerate colder temperatures has facilitated colonisation even in temperate zones, unlike Aedes aegypti, which remains largely tropical.

Behavioural Traits

The Asian Tiger Mosquito is known for:

• Aggressive daytime biting: Active mainly in the early morning and late afternoon.
• Short flight range: Typically less than 200 metres from its breeding site.
• Preference for humans and mammals: Females are strongly anthropophilic but can also feed on other warm-blooded animals.
• Resting sites: Shady areas such as vegetation, indoor corners, and beneath furniture.

These behavioural traits, combined with its adaptability, make it a persistent pest in urban and rural environments alike.

Public Health Importance

Aedes albopictus is a vector of numerous viral diseases, collectively known as arboviruses (arthropod-borne viruses). Though historically considered a secondary vector compared to Aedes aegypti, it has emerged as a major threat due to its expanding range and vector competence.

Major Diseases Transmitted

1. Dengue Fever:
   • Transmits dengue virus (DEN-1 to DEN-4).
   • Causes fever, headache, muscle pain, and, in severe cases, dengue haemorrhagic fever or shock syndrome.
2. Chikungunya:
   • Characterised by fever and severe joint pain.
   • Major outbreaks have been linked to Aedes albopictus in Asia, Africa, and Europe.
3. Zika Virus:
   • Causes mild fever, rash, and conjunctivitis but is associated with microcephaly and congenital defects in newborns.
4. Yellow Fever (secondary vector):
   • While Aedes aegypti is the main vector, A. albopictus can play a secondary role in transmission under suitable conditions.
5. Other Arboviruses:
   • Includes Ross River virus, Mayaro virus, and West Nile virus in certain regions.

Environmental and Climatic Adaptability

The success of Aedes albopictus as an invasive species is due to its ecological flexibility.

• Egg resilience: Ability to survive desiccation and cold temperatures.
• Overwintering capability: In temperate regions, eggs enter diapause (dormancy) during winter and hatch in spring.
• Rapid adaptation: Ability to exploit new habitats and climates.
• Urban tolerance: Thrives in cities, suburban areas, and even rural settings with human activity.

Climate change, with increasing temperatures and altered rainfall patterns, is expected to expand the mosquito’s range further into new territories.

Control and Prevention

Control of Aedes albopictus requires integrated vector management combining environmental, chemical, and biological methods.
1. Environmental Management

• Elimination of breeding sites such as tyres, buckets, and flower pots.
• Covering and cleaning of water storage containers.
• Regular inspection of domestic and public spaces.

2. Chemical Control

• Use of larvicides (e.g., temephos, pyriproxyfen) in breeding sites.
• Space spraying and fogging during outbreaks using pyrethroid-based adulticides.

3. Biological Control

• Introduction of larvivorous fish (Gambusia affinis).
• Use of Bacillus thuringiensis israelensis (BTI), a bacteria that targets mosquito larvae.
• Genetic control methods, such as releasing sterile or Wolbachia-infected mosquitoes to reduce breeding success.

4. Personal Protection

• Wearing long-sleeved clothing and using repellents containing DEET, picaridin, or lemon eucalyptus oil.
• Installing window screens and mosquito traps.
• Community participation in vector control programmes.

Ecological Role and Impact

Although primarily regarded as a pest, Aedes albopictus also plays a minor ecological role as part of the food web. Its larvae serve as prey for aquatic organisms such as fish and dragonfly nymphs. However, its invasive nature disrupts native ecosystems by outcompeting indigenous mosquito species, sometimes reducing local biodiversity.

Overall Perspective

The Asian Tiger Mosquito (Aedes albopictus) epitomises the challenges of managing disease vectors in a globalised and changing world. Its combination of ecological adaptability, egg resilience, and aggressive biting behaviour has allowed it to spread across continents, turning it into one of the most notorious invasive insect species.