Anophèles

Most common species of mosquitoes

in the control of disease vectors

By Julien Baylet

Summary

Anopheles larva are the only type of mosquitoes that have an atrophied respiratory siphon which forces them to float horizontally on the surface of water and makes them easily identifiable when compared to similar species (Ochlerotatus and Culex). Because of its unique anatomy, the Anopheles larva floats at a shallower depth than other species and occupies a different ecological niche, feeding on different nutrients. When observed using a microscope, the larva will tend to create miniature currents around its body using its mandibles that will suck in floating debris used for feeding. It also has a rotatable head that can turn in 180° angle to pick up floating and underwater food. Anopheles are also notable as an important disease vector in the province of Quebec which will be further discussed in this article.

Introduction

Anopheles larva share similar characteristics to other targeted species and can therefore be controlled using similar techniques. In Quebec, the most notable Anopheles species are: An. earlei, punctipennis, quadrimacultus et walker.

Morphology

Anopheles larva are easily identifiable because of their atrophied respiratory siphon which is unique to this specie. This forces them to float horizontally on the water surface in order to breathe. This floating position favorizes filter feeding of drifting biological particles.

 

*Anopheles can also be differentiated when observing its unique mouth brush pattern (see figure 1).   

 

Habitat

Anopheles larva live in areas that are always submerged with water such as swamps and bogs because their eggs are vulnerable to desiccation. Using the hairs around its body, they are able to ‘’float’’ on the surface of water and filter feed by creating a current with their body.  They mostly feed on microalgae which gives them a greenish coloration during the last larval stage.

 

They are commonly found in flooded pits, filled barrels used to collect rainwater, swamps next to newly built districts or in water accumulating holes in forests.

Development Cycle

Anopheles survive winter as adults in diapause. As soon as outside temperatures are appropriate, the eggs hatch. Throughout spring and summer, many generations of Anopheles will develop and reproduce. When fall begins, individuals that are still at the larval stage will die while those at the pupal stage will rapidly transform into adults in order to survive the winter to come.

Adults come out of their diapause at the end of May and will feed on their host at that time to begin their oviposition. Once the laying of eggs is completed, a new generation will hatch in bodies of water at the end of June. This will be followed by two other generations until fall when surviving female adults will go into diapause. 

Efficient population control

Anopheles larvae are extremely sensible to Bacillus thuringiensis (israelensis) as the bacteria tends to float on water and contaminate the microparticles used as food.

The best way to avoid the development of this specie if through education as it is easy for individuals to empty sources of stagnant water such as barrels, pools and abandoned fountains.

As a final note, Anopheles species are not considered abundant but are notable for their capacity to transmit diseases through their bloodmeal. Making them an important vector that requires close study.

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

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