Principal specie of the Mansonia genus
Insectes piqueurs, vecteurs de maladies, lutte biologique
Auteur: Julien Baylet
The mosquito specie Coquillettidia perturbans has an intriguing larval stage because of its specialised breathing technique which gives it the ability to survive in lower depths of up to 80 cm underwater. Their short breathing siphon (which is as large as it is long) has a unique deformation at its extremity and looks like a black robust tooth. The larva uses this specialised appendage to pierce through the trunk of specific aquatic plants in order to breathe the air circulating through it. This strategy gives the larva a chance to hide between the dense root system of aquatic plants and hide from potential predators. As they live in unique habitats different from all other mosquito species, they are not as sensible to normal products normally used in anti-mosquito operations. This is why Bacillus sphaericus is favoured when dealing with this specific specie. The bacteria in this product will develop in larva corpses and thrive in the environment for up to a month following spreading. As a final note, this specie is an important and aggressive vector of transmissible diseases. It is therefore prioritized in population control operations as the larvae are a challenge to detect in their environment.
When identifying mosquitos during their larval stage, the main morphological feature to observe is the respiratory siphon. For most species this appendage is used to breathe air directly from the surface of water but in the case of Coquillettidia perturbans, their siphon is small and deformed like as claw to pierce through aquatic vegetation. With this strategy it can camouflage in hard to get areas of swamps to avoid predators and gain access to regular food sources.
Because of its ability to live underwater, Coquillettidia perturbans lives in aquatic areas at a depth of 40 to 80 cm underwater populated by plants such phragmite, reed, cane and water lily.
Because the larvae survive at such deep depths, they have to deal with lower thermal conditions. The cold water slows the natural development of the larvae. At the end of June, beginning of July, the eggs hatch and develop until they attain stage 3 or 4. They then go into a diapause where all their vital systems decelerate to survive the extreme weathers of winter. The following year, during the month of May, they morph into fully developed adults.
Efficient Population Control
When dealing with Coquillettidia perturbans, the main goal is to get the larvicide deep inside the body of water. For many decades already, Bacillus sphaericus has been used as the main controlling agent for two important reasons. First, these bacteria do not float and will sink at the bottom of swamps. Secondly, they can thrive and duplicate for up to a month after treatments by surviving inside larvae corpses until they come into contact with a live larva to predate.
If the targeted area is artificial or small scale such as a private garden or an old pool transforming into a swamp, it is possible to avoid using any larvicide. The larvae can be eliminated simply by removing the aquatic plants or draining some of the water to make it shallower. This will make it more difficult for larvae to breathe properly and will eradicate a majority of the population.
By having a long-term planning of population control operations for Coquillettidia perturbans, it is possible to gradually lower the number of individuals each year. This means that less and less product needs to be used which will have a positive impact on the targeted ecosystems. This gradual approach is favoured as a permanent solution at CFR.
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Publication date: November 27, 2015