Mosquito and its life cycle

  • Mosquitoes are two-winged flying insects that suck blood from humans and other animals.
  • They are found all over the world but are mostly common in humid and temperate climate.
  • They are generally found in the dark places such as bushes, holes in the trunk of the trees, corners of the room, bookcase, near ponds and ditches.
  • Nowadays they are also found at the higher altitudes than the mild hilly regions due to climate change.
  • They are carriers of a number of diseases, mostly in the tropics, causing illness and death on a large scale.
  • They are nocturnal in feeding habit but in day time biting also occurs.
  • Some species prefer biting at certain hours, at dusk and dawn or in the middle of the night.
  • Female generally feeds on blood of humans and animals and male feeds on fruits and flower juices.
  • For that reason female mosquitoes are only responsible for causing diseases not the male.
  • Female mosquito has piercing and sucking type of mouth parts while male has only sucking type of the mouthparts.
  • They can fly a long distance in a single day, about 20-30 km in a night and about 2 to 3 hours continuously without rest.
  • Culex tarsalis and Anopheles freeborni are the two main types of mosquitoes which are common in Nepal.

A)External morphology

  • They have a small, soft, slender body, long jointed legs, needle shaped piercing and sucking mouth parts and body covered with minute scales.
  • It measures about 3-4mm in length and the body is grayish-black in colour.
  • The body is divided into three regions: head, thorax and abdomen.
  • The head of the mosquito is very small and almost spherical which is connected to the thorax by means of short and narrow segment or neck.
  • It bears a pair of kidney shaped compound eyes, a pair of antennae and the mouth parts called the palps and the proboscis.
  • The eyes are comparatively big in proportion to the head.
  • Each of the antennae is made up of 13 segments with whorls of hairs.
  • The second segment of each antenna possesses the hearing organs called Johnston’s organs.
  • Male has long hairs as compared to female on their antenna.
  • The thorax consists of three regions: very small prothorax, large mesothorax and small metathorax.
  • Each segments of thorax consists of a pair of long jointed legs and mesothorax consists of a pair of wings with halters or balancers.
  • The wings are larger in the female than in the male.
  • The vibration of wings results in buzzing sound.
  • The abdomen is slender and made up of 9 segments.
  • An anal opening and a genital opening is present in abdomen.
  • The 9th segment of male bears an anal style that helps in copulation.

B)Life-cycle

  • Mosquitoes have four distinct phases in their life cycle: egg, larvae, pupae and an adult.
  • They show complete metamorphosis in their life-cycle as they have all phases.
  • The two sexes copulate during flight in the evening where the male gets attracted to the female by her high-pitched whine.
  • The female usually mates only once but produces eggs at intervals throughout their life.
  • In order to be able to do so, female requires blood meal.

 

Image result for life cycle of anopheles mosquitoImage result for life cycle of culex mosquito

 

 

a)Eggs

  • A female mosquito lay about 30-300 eggs depending upon the species at a time.
  • The female anopheles lay about 30-100 eggs at a time which are laid separately and horizontally on the surface of water.
  • The eggs are spindle shaped having lateral air floats.
  • Similarly, a Culex lays about 200-300 eggs at a time which are glued together to form a small floating raft.
  • The eggs of Culex are cigar-shapede. their upper end is narrow and pointed while the other end is broad and rounded.

 

Image result for eggs of culex                                              Image result for eggs of anopheles

 

b)Larvae

  • The eggs are hatched into larvae within 2-3 days under suitable condition.
  • These are transparent and emerge from the lower end of each egg.
  • They show caterpillar-like movement so they are also called wrigller.
  • The body of larva is divided into head, thorax and abdomen.
  • The head bears of a pair of compound eyes and mouthparts.
  • The front part of the mouth possesses feeding brushes which help to feed.
  • The thorax is broad, un-segmented and has no appendages.
  • On the lateral sides, three pairs of tufts of hairs are present.
  • The abdomen is made up of nine segments each of which bears bristles.
  • The dorsal side of eighth segment possesses a siphon which bears a pair of
  • Spiracles help in respiration.
  • Tracheal gills are present in ninth segment around the anus.
  • This stage lasts for about 2 weeks during which it moults three to four times enlarging its size with each moulting.
  • 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 surface of water.
  • The fully grown larva lives in water and develops into pupa.

 

Image result for larvae of culex                   Image result for larvae of anopheles mosquito

larvae of Culex                                                                   larvae of Anopheles

 

c)Pupa

  • Commonly known as tumbler.
  • Body is comma shaped and can be divided into anterior swollen part called cephalothorax and the posterior elongated hook-like abdomen.
  • The pupa is enclosed in transparent membrane called puparium.
  • Pupa of mosquito is very active as compared to other insects.
  • It always swims with the help of its paddle.
  • Mouthparts are absent so it does not feed on anything.
  • It respires with the help of respiratory trumpets.
  • It lasts for about 2-7 days during which the adult organs are developed.

 

Image result for pupae of culex mosquito                    Image result for pupae of anopheles mosquito

pupa of Culex                                                                                            pupa of Anopheles

 

d)Adult

  • The pupal stage lasts for short duration.
  • The pupa develops the body organs inside it after the completion of the metamorphosis.
  • Thus, a perfect adult insect, an imago is formed.
  • The mosquito is completely young in this stage which emerges when the pupal skin splits.
  • The wings get dried by vibrating after which the mosquito flies in air within 5-10 minutes.
  • The male and female mates and the female gets ready to lay eggs again.
  • In this way the life cycle of mosquito continues.

 

Image result for adult culex                   Image result for adult anopheles

adult Culex                                                                                                      adult Anopheles

 

Mosquito and its life cycle

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