Our objective is to study the life cycle of a mosquito.
The mosquitoes are a family of small, midge-like flies. Like all flies, mosquitoes go through four stages in their life - egg, larva, pupa, and adult. We call this as the life cycle. Each of these stages is morphologically different from the other, with even the habitat of each stage differing. The first three stages - egg, larva and pupa are largely aquatic, whereas the adult stage is aerial.
We will now look at the four distinct stages of development in the life cycle of a mosquito.
The eggs are laid one at a time and they float on the surface of the water. Normally the eggs are white when first deposited, then darken to near black within a day. They hatch in one to three days depending on the temperature. Eggs left on moist soil can last for up to a year, until the ground is flooded again, before hatching.
In the case of Culex and Culiseta species, 200-300 eggs are stuck together in rafts. Anopheles and Aedes species do not make egg rafts but lay their eggs separately. Culex, Culiseta, and Anopheles lay their eggs on water while Aedes lay their eggs on damp mud. The eggs generally do not hatch until the place is flooded. Most eggs hatch into larvae within 48 hours. When the larvae are ready to hatch, they use a small temporary ‘tooth’ on their head to break open the egg along a suture that was made by it.
Mosquito larvae, commonly called ‘wigglers’ or ‘wrigglers’, live in water from 7 to 14 days depending on the water temperature. Larvae swim either through propulsion with their mouth brushes, or by jerky movements of their entire bodies, giving them the common name of ‘wigglers’. The larva begins to feed on bacteria and decaying organic matter on the water surface, soon after they hatch out of eggs. They spend most of their time hanging upside down at the surface, sucking in oxygen through the siphon. The siphon is located at the base of their abdomen and is similar to a snorkel. Brushes that are located in front of their mouths collect the food. Anopheles larvae do not have a siphon and they lay parallel to the water surface. The larval stage lasts for a few days to a few weeks, during which the larvae shed several layers of their outer skin, called moulting. This allows further growth.
After the larvae have completed moulting, they become pupae. This is the stage in which they undergo metamorphosis to become an adult mosquito. The pupal stage is a resting, non-feeding stage. Mosquito pupae are commonly called ‘tumblers’. The pupa is lighter than water and therefore floats at the surface. The mosquito pupa is comma-shaped. The head and thorax are merged into a cephalothorax, with the abdomen curving around underneath. At one end of these curved bodies is the large head and at the other end is the flippers used for swimming. They must take in oxygen from time to time through two breathing tubes known as ‘trumpets’. After a few days or longer, depending on the temperature and other circumstances, the pupa rises to the water surface, the dorsal surface of its cephalothorax splits, and the adult mosquito emerges.
The newly emerged adult rests on the surface of the water for a short time to allow itself to dry and harden its parts. Also, the wings have to spread out and dry properly before it can fly.
Adult mosquitoes have a head with two large compound eyes, a thorax, a pair of scaled wings and six jointed legs. They also have antennae and a proboscis. Adult mosquitoes mate within the first few days after emerging from the pupal stage.
It is the carbon dioxide that we exhale, and the lactic acid from our sweat that combine to make us smell like a mosquito buffet. Mosquitoes can pick up these smells from 100 feet, and they can also feel our body heat and notice movements.
Only female mosquitoes have the mouth parts necessary for sucking blood. When biting with their proboscis, they stab two tubes into the skin, one is an anti-coagulant to keep the blood flowing and is a mild painkiller that helps them escape detection, the other helps to suck blood. They use the blood not for their own nourishment but as a source of protein for their eggs. For food, both males and females eat nectar and other plant sugars.
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