There are approximately 159 species of mosquitoes in Sri Lanka, 52 of which belong to the Aedes (Meigen) genus. Among these Aedes species, Aedes aegypti and Aedes albopictus are the vectors that transmit the dengue virus to humans. These two types of mosquitoes can be easily differentiated by the unique markings on their bodies.

Life Cycle

The life cycle has 4 distinct stages, namely; egg, larva, pupa and adult (Fig1). The first three stages are aquatic and the adult is terrestrial. The time taken to complete the life cycle is usually 7-10 days depending on the environmental factors.

Eggs

The female mosquito lays eggs (oviposit) singly on damp inner surface of wet containers above the water level, preferably with clear water. The eggs are smooth, long, ovoid shaped and about 1mm long. When first laid, the eggs appear white but within minutes they turn shiny black.

Within about 2 -3 days, the eggs hatch to larvae. The eggs can withstand dry weather conditions and retain viability for up to six months or longer.

Larva

The larval stage consists of 4 stages, namely, 1st, 2nd, 3rd and 4th instar larvae (Fig 1). Larvae feed on organic matter contained in the water except late 4th instar. All the larval instar stages are mobile with a characteristic “s” shape movement of the body. At the end of larval period of 4 - 5 days, the 4th instar larva develops in to a pupa. The mosquito larval body consists of three major parts; head, thorax and abdomen (Fig.1).

Pupa

The pupa is comma shaped and mobile. This stage is the final aquatic stage of the mosquito’s life cycle and it develops into adult mosquito within 1-2 days. Pupa is a non-feeding stage. Pupal body consists of cephalothorax and abdomen (Fig 1). The density of pupae is a crude proxy to the adult mosquito density.

Adult

Adult mosquitoes are small to medium-sized (approximately 4 -7 mm), dark with white markings/ bands on the body (Fig. 1). The adult life span (longevity) can range from 02 - 04 weeks depending on environmental conditions such as temperature and humidity.