Mosquitoes

Le 23 March 2020

Mosquitoes are a family of insects called Culicidae. 

Source of nuisance by bites, they are the most important group of vectors of pathogenic agents transmissible to humans: the plasmodium (causing malaria), wired (parasitic worms)

They are present as soon as a surface of fresh or brackish water, even reduced or temporary, is available.

Morphology of the various stages of development

Mosquitoes are holometabolous insects going through 4 stages of development: egg, larva, nymph and adults. The first three are aquatic, the last aerial. The total duration of this development, strongly influenced by the temperature, is 10 to 15 days for the tropical zones of the world which gather the highest densities of species.

Life expectancy can vary from two to three weeks for some species, to several months for others. In diapause, the life expectancy of some mosquitoes can reach several months

Ecosystem services

The mosquito plays a role in many food chains. Both male and female adults participate in pollinating plants by feeding on their nectar.

Mosquitoes have a rhythmic, seasonal and nycthemeral activity.

For mating, males and females form a swarm, shortly after sunset, a few meters from the ground. Each female will be fertilized once for her entire life. The humming characteristic of mosquitoes is only emitted by females. It allows males to spot them, each species having its own characteristic frequency.

The females are blood-sucking, the blood meal being essential for the laying. For blood-sucking species, blood supply is necessary for spawning. The adult female bites the animals to collect their blood, which contains the proteins necessary for eggs to mature.

During the bite, the female injects anticoagulant saliva which, in humans, causes a more or less significant allergic inflammatory reaction depending on the individual: it is the formation of an "itch". The amount of blood collected varies from 4 to 10 mm3 in 1 to 2 minutes.

Behaviour

Forty-eight hours after taking the blood meal, the fertilized females lay their eggs, depending on the species: on the surface of permanent or temporary water, stagnant or running, in natural or artificial receptacles or on floodplains (swamp , rice field…). The total fertility of a female varies according to the species from 500 to 2000 eggs. These eggs develop in one to two days and hatch, giving birth to first-stage aquatic larvae which have a respiratory siphon in contact with air at the end of the abdomen

The duration of the larval stage is approximately seven days (if the external conditions are favorable: water quality, temperature and food mainly). Adults live according to conditions and species for 15 to 40 days, except for certain species whose females can overwinter.

The larvae feed and remain at rest below the surface of the water, breathing through their spiracles which are flush with the surface. Finally, some genera of Culicinae have their larvae immersed, breathing through the stem of a plant in which they insert their siphon (Coquillettidia, mansonia, some species of the genus Mymomyia). The larvae go through four larval stages, resulting in an increase in their size, and metamorphose into a pupa.

The nymph is aquatic and breathes atmospheric air using these two respiratory trumpets. The abdominal end of the pupa is flattened in paddles or fins. The nymph does not feed. It is a stage of transition to the adult during which the insect undergoes profound physiological and morphological changes.

From the pupa the flying adult will emerge after two to five days.

The bite and its treatment

The bites can be completely painless but can go as far as causing more serious allergies, going exceptionally to anaphylactic shock. 

Various remedies are more or less effective depending on the person and the time of application. Marseille soap has a calming effect (rub in the place of the bite). 

Direct application of a cloth soaked in very hot but not boiling water can block the release of histamine around the bite for a few hours. Finally, any cortisone-based cream is effective given their anti-inflammatory effect.

Main diseases transmitted to humans by mosquitoes:

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