World Mosquito Day 2020

Lisa Stalknecht
11 August 2020

Today is world mosquito day. Mosquitoes, who doesn’t know them? The name mosquito comes from the Spanish word which means ‘Little fly’. Mosquitoes are very infamous for their character trait to suck our blood on leave an itchy bump. But, why are they biting humans?

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Figure 1: Common house mosquito (Source: GOV.il)

Mosquito

Mosquitoes are all over the world. There are more than 3000 mosquito species. With all slightly different habitats and habits they are categorized in 39 genera. Of all the mosquito species, around 113 species live in South-Africa. The diet of mosquitoes exists of nectar from flowering plants. However, when the females are ready to mate, they need proteins and lipids. They need this to lay eggs. And this is when mosquitoes start to bite mammals. The males however do not need blood and are satisfied with their nectar. The females hunt at night and rest during the day or after they had their blood meal. Their preys include of course, humans but also birds like robins, jays and sparrow and waterfowl such as geese and ducks. Not only birds are on their menu; they also feed on small mammals for example racoons and even snakes, lizards and some species of fish. In South Africa the most common types of mosquitoes are the black and white striped mosquito (Aedes albopictus) and the common house mosquito (Culex pipiens). Both species do not transmit malaria, but the black and white-striped mosquito can transmit the dengue virus.

Life-cycle

To lay their eggs female mosquitoes need stagnant water. This water can be in a bucket, in a creek or even in car tire as long as there is water in it. The cycle of a mosquito exists of four stages: egg, larva, pupa and adult. When the female lays her eggs, she lays around 100 eggs at a time. The black eggs are robust and can survive for up to 8 months without drying out.  They stick to the walls and hatch when the level rises and covers the eggs. The larvae live off organic and vegetative materials they find in the water. The larvae molts three times and after that the larva turns into a pupa. The pupa develops until the mosquito, is an adult then the mosquito is ready to crawl out of pupal skin and leave the water. The females mate and then search for a blood meal to repeat the whole life-cycle again. The life-cycle of a mosquito, from egg to adult, can take up to five days. In some cases, it takes longer, around 10 to 14 days.

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Figure 2: Life cycle of a mosquito. (Source: megacatch.com)

Diseases

Mosquitoes are feared due to the fact that they are vectors of diseases. They are especially feared because they can transmit the plasmodium parasite, which causes malaria. Malaria is the most common disease transmitted by mosquitoes. The mosquito that is responsible for the spreading of this parasite is the female Anopheles mosquito. The plasmodium parasites enter the body during a mosquito bite. Although there are many different types of the plasmodium parasite, only 5 of them causes malaria. The most common type of plasmodium is the Plasmodium falciparum - this type is responsible for the most malaria deaths worldwide and is mainly found in Africa.

Another disease transmitted by mosquitoes is dengue. The mosquitoes that transmits dengue are the Aedes mosquito, which include the black and white-striped mosquito (Aedes albopictus) and theyellow fever mosquito (Aedes aegypti). The Aedes family is also responsible for transmitting other diseases like yellow fever and the zika virus but, do not worry; the dengue virus, the zika virus and yellow fever are not transmitted in South-Africa. Dengue is caused by the dengue virus (DENV). There are four serotypes of DENV, this means that it is possible to be infected four times. All four serotypes cause Dengue and are related to the Flaviviridae family. The serotypes are distinct from each other, but closely related. When infected by one the serotypes (DENV1, DENV2, DENV 3 or DENV4) you will get a lifelong immunity against that specific serotype. Throughout the tropics the virus is widespread. Many DENV infections are not lethal and produce mild illness. When infected, only one of four people will get sick. However, when you are sick and having an acute flu-like illness caused by DENV this can develop, in some cases, to severe dengue. Severe dengue is dangerous and needs to be treated immediately when you have symptoms.

Predators

Mosquitoes have various predators which can reduce mosquito populations. Some predators eat the larvae of mosquito and others feed on adult mosquitoes. The dragon fly, for example, feeds on both. When flying out of their aquatic habitat, dragonflies can easily catch the adult mosquitoes. Other animals that eat mosquitoes are some bird species, such as the yellow warbler and swallows. Nighthawks, (also called, mosquito hawk) and various other bird species that have mosquitoes on their menu. Fish are the most effective natural predators of mosquitoes.  It is believed that the mosquito fish is the most effective mosquito hunter and have been introduced in many water courses the world over, even here in the Groot River in Nature’s Valley. Mosquito larvae are their primary food source and they can eat hundreds of larvae on a day. Sadly, mosquito larvae are not their only food source and they also feed on larvae of other invertebrates. and can also have severe impacts on local fish species, through direct competition for food and habitat.

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