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Principal specie of the genus

Culex

considered in the fight against biting insects and vectors of diseases

By Julien Baylet

Summary

The Culex is one of the most studied genus in North America because of its ability to pass on many harmful parasites and virus to humans during summer when temperatures rise above 40°C. These mosquitos are considered very active for two reasons. In the first place, they are extremely resistant to pollution and can develop in sewers and cesspools. Secondly, once they mature into adults, the reproducing females prey on birds and collect some of their infected blood before biting mammals such as humans and transmit pathogens.

Canada’s Culex are known to be potential carriers and transmitters of diseases such as the West Nile Virus, paludism, malaria and dengue. Although these diseases are rare in Canada, population booms of Culex can have a devastating impact on a whole country or a whole continent. This present document investigates the principal Culex species that can be observed in the south of Quebec as they are of particular interest to public health.

Morphology

The breathing siphon of Culex pipiens is fixed with 4 straight pairs of hairs with the exception of the third pair which is not aligned with the rest.

Habitat

Culex species are known for their resistance to polluted environments. They can be found in sceptic tanks, sewers, abandoned tires and stagnant water holes. Cesspools are of particular interest as they are constantly filled with organic nutrients, high in temperature and close to human habitats. It is important to note that birds such as crows are favoured by Culex mosquitos to complete their blood meals while humans remain a secondary option. As a vector to many diseases, the mosquito is not sick but serves as a carrier of the viruses that will be injected into human through an exchange of blood which can be lethal.

Les soies siphonales du Culex restuans sont éparpillées tout autour du siphon. Observer les siphons est le meilleur moyen de différencier les Culex pipiens des restuans.

 

Life Cycle

 

Culex species use diapause to survive winter as adults. Once summer begins, the female adults wake up fertile and ready to lay their eggs. The larvae then hatch and develop rapidly to become mature in about 2 weeks. They then restart the cycle and prey for bloodmeals to reproduce.

Efficient Population Control

Because it carries multiple diseases, Culex species are a danger to the health of Canadian populations. They are the main vector of the West Nile Virus which can be lethal to newborns, seniors and those with a weak immune system.

When controlling for this particular species, methoprene, an accepted chemical larvicide, is used in sewer systems and cesspools. This product stops the development of affected individuals during their nymph stage of life. It is active for up to a month after spread and has a notable ecological impact in the artificial environment. The use of methoprene is a great alternative to biological products as it requires less volume to attain the desired effect.

A second method used is Bti in a granular form which is deposed in the same sewer systems but which requires a higher frequency of spread as it only stays active in its environment for about a week.

For more information on biological treatment: Control of biting insects.
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Publication date: November 27, 2015

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