Mosquitoes are harmful insects that belong to class Tresecta of phylum Arthropoda. They not only suck blood from humans and other vertebrates but also transmit various diseases like malaria, filariasis, encephalitis, dengue, yellow fever, etc. from infected person to another. Therefore, mosquitoes are considered harmful insects. Nearly about 3000 species of mosquitoes are found throughout the world. Among them, about 100 species of mosquitoes transmit various diseases. Culex, Anopheles and Aedes are the most common species of mosquitoes found throughout tropical and sub-tropical regions.
Mosquitoes become active during night. They are found in damp and many places of tropical and sub-tropical countries. Female mosquitoes suck blood from humans and other vertebrates but male mosquitoes do not suck blood. They live on nectar of plants, Because of blood-sucking habit, female mosquitoes are important than males, because female mosquitoes are the vectors of various diseases like malaria, encephalitis, meningitis, dengue, yellow fever, filariasis, etc. Generally, mosquitoes live in dark place and comers of room, bushes, etc. Mosquitoes lay eggs in water where they complete their life cycle.
The body of an adult mosquito can be divided into three distinct parts they are head, thorax and abdomen. The body is small, slender and about 3-4 mm long. The grayish-black body of mosquito remains covered with tiny scales. The head is small and spherical in shape. It consists of a pair of compound eyes, a pair of jointed antennae and piercing and sucking type of mouthparts. The mouthparts of mosquitoes consist of a needle-like proboscis which is used for sucking blood.
The middle part of the body is called thorax. It can be divided into three parts, viz. prothorax, mesothorax and metathorax. Each part of thorax consists of a pair of long jointed legs. The mesothorax consists of pair thin, narrow and membranous wings. The wings of female mosquitoes are larger than that of male mosquitoes. The metathorax consists of a pair of rudimentary wings called halters or balancers which vibrate and produce the characteristic sound of mosquitoes.
The abdomen of mosquitoes is small and cylindrical. It consists of nine segments. The ninth abdominal segment contains anus. Mosquitoes show complete metamorphosis in their life cycle. It means that the life cycle of mosquitoes completes in four distinct stages. They are (i) Egg (ii) Larva (iii) Pupa and (iv) Adult. Mosquitoes are found in gardens, crop-fields, near sewage, etc. but they need water to reproduce. Out of four stages of the life cycle, first three stages, i.e. egg, larva and pupa develop in water.
In mosquitoes, mating takes place in the air while flying. The female mosquito takes a blood meal after mating and then lays eggs in stagnant water of puddles, ditches, and pools. After mating, a female mosquito lays eggs in water. Some mosquitoes lay eggs in clean water and others lay in dirty water. A female Anopheles mosquito lays 40 - 100 eggs at a time in clean resting water. The eggs contain lateral air floats and are laid separately. A female Culex mosquito lays 200-400 eggs at a time in dirty water. The eggs are narrow and elongated without air floats. The eggs of Culex mosquito are cigar-shaped. Which remain attached together forming a raft. The raft floats on water like a boat.
Larva is the second stage of the life cycle. In favorable condition, the egg hatches into a tiny larva within 2-3 days. The larva is small and transparent. The larva of a mosquito moves in water by wriggling movement. Therefore, it is called a wriggler.
The body of a larva can be divided into the head, thorax and abdomen. The head consists of a pair of compound eyes, a pair of antennae and chewing types of mouthparts. The thorax of larva is wider than the head. It consists of three pairs of lateral tufts of hairs. Legs are absent in thorax.
The abdomen of larva is elongated having nine- segments. A respiratory siphon is present on the 8" segment and four tracheal gills are attached to the segment each abdominal segment bears a pair of bristles
When at rest, the larva of Anopheles remain parallel to the surface of water but the larva of Culex hangs with its head downwards at an angle of 45 to the surface of water.The respiratory siphon of the larva of Anopheles is shorter than that of Culex. The larva of mosquito moults 3-4 times. At the last moult, the larva changes into a pupa within two weeks.
Papa is the third stage of the life cycle. In favorable condition, each larva develops into a comma-shaped pupa within two weeks. The body of a pupa can be divided into two parts, viz. cephalothorax and abdomen. The cephalothorax is the fused form of head and thorax. It consists of a pair of compound eyes, a pair of antennae and a pair of respiratory trumpets. The abdomen is nine segmented and the last abdominal segment consists of a pair of large swimming paddles,
Unlike other insect's pupae, the pupa of a mosquito is quite active. It swims actively in water. The pupa does not eat as there is no mouth but breathes through respiratory trumpets. The pupa changes into an imago within 2-7 days in favorable condition.
On favorable condition, each pupa changes into an imago within 2-7 days. A newly emerged adult is called an imago. The imago emerges out by tearing the puparium that is the cover of pupa. The imago dries its wings for some time before flying
Malaria is the most common disease transmitted by mosquitoes. It is transmitted by female Anopheles mosquitoes and caused by a protozoan parasite called Plasmodium. This disease is common in tropical and sub-tropical regions.
When a female Anopheles mosquito bites a person suffering from malaria, it takes numerous Plasmodium parasites along with blood. These parasites complete a part of their life cycle in the body wall of mosquitoes and finally come in the salivary gland of the mosquito. When the mosquito containing infective stages of Plasmodium in the salivary gland, bites a healthy person, the person acquires infection. Then these parasites enter the liver through blood stream and complete a part of their life cycle and finally infect red blood cells. The symptoms of malaria occur when Plasmodium parasites infect and destroy red blood cells.