Principal specie of the genus
Ochlerotatus et Aedes
considered in the fight against biting insects and vectors of diseases
By Julien Baylet
Mosquitos of the Ochlerotatus genus come to life during spring. This means that reproducing adults appear and are a problem from March to June. Many species eggs come out of their diapause and hatch in melting snow water. Others prefer to wait for important rains to flood specific areas where they can grow from egg to adult within three to five days, as is the case for Aedes vexans. The Ochlerotatus genus is rich in its number of species and has a large spectrum of physiologic particularities and specific behaviours to survive in various habitats. This document will look at the principal Ochlerotatus species that inhabit the south of Quebec and are subject to population control.
The Ochlerotatus genus is composed of species that are of particular interest to population control operations as they are susceptible to carrying dangerous human diseases.
Aedes vexans is a remarkable species as it is able to develop from egg to adult in less than a week.
Without the use of a microscope, it is impossible to identify larvae of this specie. With the use of a zooming device it is becomes easy to do so. As with most mosquito larvae, the observation of its respiratory siphon is the best indicator.
To identify an Aedes vexans you must note the bands of scales at the base of each tergite (the backplate of an arthropod) which is not totally straight but has a “ ^ “ shape in its center where the scales are shorter.
The rapid development of Aedes vexans can be explained by its habitat. Egg laying females are able to spot areas that are prone to regular water accumulations. They place their eggs in humid soils which are inundated as soon as rain falls. Larvae hatch in tiny amounts of water and on flat terrains where the sun heats the liquid. The most common areas where they develop are puddles, pools, gutters, pots and so on.
Eggs are present on the ground all year long and can stay active for up to 7 years. They stay in a state of diapause in humid areas and hatch when conditions such as heavy rains and high temperature are met.
During the month of September, before the cold season begins, female adults lay eggs and transmit a chemical message that keeps them in a state of diapause until the next year.
Efficient Population Control
As with most mosquito larvae, Aedes vexans can easily be eliminated using Bacillus thuringiensis (variété israelensis), a biological larvicide which is specific to some dipteran genus. Many scientific studies have been completed on the product by the MDDELCC and each treatment requires their approbation and special permits.
This is the first mosquito species to emerge in the spring. During that time, they represent one of the most important population in number of individuals during the month and a half of their mating season. For this reason, they are extremely aggressive towards humans until the end of May. This species prefers forested areas and can fly up to one kilometer from their point of emergence.
When identifying an Ochlerotatus abserratus larva, the taxonomist must consider two important regions, the head and the anus. Specific pairs of hairs known as 5C, 6C and 7C can be observed on the head while two other pairs of anal hairs known as 2-X and 3-X can be identified. When looking at the image, the arrow points towards the saddle which is completely enveloped in an anal segment during the fourth larval stage.
When it comes to other morphological characteristics, they are not necessary to identify an Ochlerotatus abserratus.
Ochlerotatus abserratus grows in natural habitats, usually in forest areas. It is captured in peat bogs and riparian strips that crisscross certain remote residential areas or semi-rural areas.
Everything goes very fast for Ochlerotatus abserratus as they start their development once snow is melting. After 2 months as larvae, they emerge and female adults have 2 months to reproduce and lay eggs at the end of July.
Efficient Population Control
Bacillus thuringiensis (israelensis) is the best adapted biological larvicide to prevent and kill Ochlerotatus abserratus.
Because of their early arrival, water holes temperatures are low, usually under 5°C, which lessens the rate of success of Bti. Knowing this, CFR is able to adapt its spreading operations to take into account this reality.
Les particuliers ne peuvent pas vraiment solutionner ce problème, car les terrains sont généralement publiques, privés, sécurisés ou protégés. De ce fait, le particulier ne peut que signaler le problème à la municipalité qui envisagera alors de nous engager pour traiter le secteur.
During its fourth larval stage, Ochlerotatus canadiensis is one of the largest species because of the high density of its exoskeleton. When identifying a larva of this specie, the taxonomist must observe its pairs of hairs on its breathing siphon.
Ochlerotatus canadiensis is different from other Ochlerotatus because of….
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Publication date: November 27, 2015