In the life history of mosquito there are four stages namely—egg, larva, pupa and imago or adult.
After sexual union the female mosquito lays about 200-400 fertilised eggs in shallow stagnant water. The eggs of Anopheles and Aedes float separately in the water, but the eggs of Culex remain together and float as a single unit.
The individual egg of Anopheles is provided with two central extensions known as air floats which are attached laterally. The eggs float horizontally on the water surface separately. After 2 or 3 days the eggs hatch into larvae.
The larvae are very much active and they feed on algae, micro-organisms etc. The body of a larva is elongated which is divisible into head, thorax and abdomen. The head bears a pair of compound eyes, a pair of antennae and a pair of feeding brush.
The un-segmented thorax bears clusters of bristles and the abdomen is provided with respiratory siphons. The larva moves to the surface of water for respiration. After about 7-10 days the larva is metamorphosed into pupa.
The pupal stage of mosquito is not stationary like other insects. The pupa moves in water but they do not feed on anything as they have no mouth aperture. It is comma (,) like structure and the head region is comparatively larger. The dorsal siphon remains above the surface of water for respiration. The pupal stage continues for 2 days.
(d) Adult or image:
After two days there is a metamorphosis in the pupa and the imago or adult is formed. The adult comes out by breaking of the pupal shell and the adult mosquito remains sometime over the shell and flies away when its wings harden.
The life cycle of a mosquito is usually completed in 15 days and the adult usually lives for about one month. (Table 15.2 and Fig. 15.3).