Morphology and life cycle of mosquitoes

Mosquitoes are harmful insects found in hot and moist places generally common during monsoon and spring seasons.
They are generally active during the hours of darkness and hide in bushes, in cupboards, book racks, dark corners etc. during the day time.
Mosquitoes are harmful to human beings because they annoy us at night, their bite is painful and irritating and they also transmit various diseases like malaria, filarial, yellow fever etc.
Both the male and female mosquitoes feed on plant juice and nectar of flowers but the females also suck blood from warm blooded animals since they need proteins for energy to lay eggs after fertilization.
Culex, Anopheles, Aedes are major genera of mosquitoes prevalent in tropical climate that transmit many diseases like malaria, filaria, yellow fever.

Morphology and structure:

The body of mosquito is very soft, small and covered with scales and is divided into head, thorax and abdomen.

1.Head:

The head is round, small and highly mobile.
It bears a pair of kidney shaped compound eyes, a pair of antennae and mouthparts.
Each antenna is made up of 13 segments with whorls of hair.
The antennae of female are long and covered with soft hairs but are bushy or feathery in males.
The second segment of each antenna possesses the hearing organs called Johnston’s organs.
The mouth parts consist of palps and proboscis.
In females, the proboscis contains needle like structures for piercing and sucking blood from animals.

2.Thorax:

The thorax is slightly arched and consists of three parts;
- Prothorax (upper)
- Mesothorax (middle)
- Metathorax (lower)
The thorax bears three pairs of jointed legs and a single pair of wings.
The second pair of wings is reduced to a pair of rod like structures with knob at their tips called the halters.
Halters help in balancing the body during the flight.
The wings are larger in females than in males. The wings during the flight beat to produce a buzzing sound.
The legs are long and jointed present on the ventral side of the abdomen. All six legs are used in walking, but only the front four are used in standing.

3.Abdomen:

It is long and narrow and consists of 9 segments.
The eighth segment consists of an anal opening on its ventral side and genital opening is located ventrally on the last (ninth) segment.

Life cycle of mosquito:

The male and female mosquitoes mate during flights in the evening. The female takes a blood meal before laying eggs to have extra nourishment for this purpose.
In warm climates, the life cycle completes in about a week to 10 days.
The life cycle of mosquitoes completes in 4 stages; egg, larva, pupa and adult.
The adult mosquito lives on land but eggs, larva and pupal stages occur in water.

Female mosquitoes lay their eggs in stagnant water of ponds and ditches.
Female Anopheles lays about 40-100 eggs at a time which are separate (not attached) and lie horizontally on the water surface.
The eggs are spindle shaped having lateral air floats.
Culex lays about 200-300 eggs at a time which are cigar shaped and without air spaces. The eggs are glued together from side to form ‘rafts’. The rafts are vertical with heavier end downward.
The whole raft is concave and floats on the surface of water.
The eggs stage lasts for about 2-3 days.

The eggs hatch out into transparent, minute worm like larvae.
Its body consists of head, thorax and abdomen.
The head is broad and has two short bushy antennae on each side.
It has two compound eyes, and mouth is situated ventrally on the head.
A pair of long hair-like bristles called feeding brushes are present around the mouth which move rapidly to set up a current of water, carrying small food particles into the mouth.
The thorax is slightly broader than the head. It has three pairs of lateral tufts of hairs, which protect from being eaten by fish.
The abdomen is 9 segmented; each segment bears a pair of lateral tufts of hairs.
Dorsally, on the eighth segment, is located a long respiratory tube or siphon, which is thrusted above the water surface so that the larva can breathe.
They also consist of 4 small leaf-like tracheal gills in the last abdominal segments which help them take O₂dissolved in water.
The larva of Culex at rest hangs at an angle from the surface of water whereas the larva of an Anopheles lies parallel to the water surface.
The larva swims actively in water by wriggling movement and hence is also called a wriggler.
It is very active and feeds voraciously on microscopic algae and other creatures as it has mandibles and maxillae for biting and chewing.
The larva stage lasts for about 2 weeks during which it molts 3-4 times and then develops into a pupa.

Pupa has a comma shaped body and can be divided into two parts: the swollen anterior part called cephalothorax (fused head and thorax) and the posterior elongated hook like abdomen.
The pupa is enclosed in a transparent membrane called puparium.
The pupa of a mosquito is very active in comparison to the pupae of other insects. It swims vigorously by flicking its abdomen.
It doesn’t feed at all as it doesn’t possess the mouth parts.
They roll and tumble in water and hence are also called tumblers.
They respire through a pair of small trumpet-shaped tubes called respiratory trumpets.
The pupa stage lasts for 2-7 days during which the larval organs are broken down and the adult organs are formed.

After complete metamorphosis, the pupal skin splits along the cephalothorax and the pupa transforms into an adult called an imago (with well developed wings and legs).
The imago dries its wings by vibrating its wings for 5-10 minutes and then flies in air.
The male and female then mate in air and female lays fertilized eggs after having the blood meal.
The adults can live up to a month or more in captivity but not more than 1-2 weeks in nature.

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