Understanding Mosquitoes

Life Cycle

Mosquitoes are well known vectors of several diseases including West Nile Virus. The mosquito life cycle is made up of 4 stages. Egg rafts are laid on standing water and are very hardy. Some species lay eggs in the fall which survive through the winter to hatch in the spring. When conditions are right, larvae hatch from the eggs and begin feeding on organic matter in the water. The larvae require the water to be stagnant as a result of their methods of breathing and eating. Larvae progress through several stages of growth and transform in pupa, which are also reliant on standing water. Adults emerge from the pupa and rest on the water’s surface before taking flight. After mating, which takes place approximately one day after emergence; female mosquitoes begin to seek a blood meal. Contrary to popular belief mosquitoes do not take blood for their own nourishment. Instead, mosquitoes feed on plant sugars. It is only the adult females that take a blood meal that is used for the development of eggs. Adult males do not take blood. The cycle begins again when the female deposits her eggs on standing water. The entire cycle can take anywhere from 7 to 14 days. Higher temperatures tend to decrease the required time for development.

Habitat

Mosquitoes are usually found in shaded areas with varying amounts of vegetation. A common factor to all mosquito environments is a source of standing water in which to breed. Different species have different preferences for breeding sites. Natural breeding sites for mosquitoes include small water filled depressions, swamps, tree holes, and sheltered areas of larger bodies of water. Many common human products present excellent alternatives to these natural mosquito nurseries, such as pool covers, bird baths, unused toys, and old tires.

Grey Bruce Mosquito Species   

There are approximately 75 mosquito species in Canada, of which 57 are found in Ontario. In 2005, trapping throughout Grey Bruce revealed a total of 27 species. However, since trapping could not be carried out in all areas and the traps used do not target all species, it is quite likely that there are more than 27 species of mosquitoes in Grey Bruce. Only female mosquitoes were identified due to the fact that males are not attracted to traps and present no risk of transmission since they do not bite.

Male Mosquito

easily distinguished from a female mosquito based on the bushy appearance of the antennae (photos are taken from Grey Bruce Health Unit samples)

The 5 most abundant groups of mosquitoes trapped in Grey Bruce during 2005 were:

1. Ochlerotatus spp.

The Ochlerotatus genus represented 46% of mosquitoes trapped in 2005. Ochlerotatus is a very diverse grouping of mosquitoes. Species such as Ochlerotatus triseriatus and Ochlerotatus canadensis are known WNV vectors. Ochlerotatus mosquitoes are among the first groups of mosquitoes to appear each season in Grey Bruce. Eggs are laid in a variety of locations depending on the species. Some larvae develop in tree holes and artificial containers while others are found in sheltered ponds. 

Ochlerotatus triseriatus

Ochlerotatus canadensis

2. Coquillettidia perturbans

The Coquillettidia perturbans species of mosquito made up 35% of mosquitoes trapped in the summer of 2005. It is a known WNV bridge vector meaning that it can transmit the virus from the bird population to humans. Coquillettidia perturbans is a night biter but will bite in the shade during the day if disturbed. It is a strong flier that will fly several kilometers in search of a host. Eggs are laid on permanent water bodies with emergent vegetation, such as cattails. The Cq. perturbans larvae attach themselves to the vegetation from which they draw oxygen; however; they can also surface to breathe.

Coquillettidia perturbans

3. Aedes vexans

Approximately 10% of mosquitoes trapped during the summer of 2005 were the Aedes vexans species of mosquitoes. Aedes vexans are West Nile Virus bridge vectors that will feed in shady areas during the day but are most active at dusk. Breeding sites include artificial containers, storm sewers, drainage ditches, marshes, streams, and a variety of other sites.

Aedes vexans

4. Culex pipiens/retuans

The Culex pipiens and restuans species of mosquitoes made up 7% of mosquitoes trapped in Grey Bruce during the 2005 season. Culex pipiens/restuans primarily bite birds but will bite humans more frequently when bird numbers begin to decline towards the end of the summer. Culex mosquitoes are the WNV vectors of greatest concern since they can spread the virus to high levels within the bird population and then transmit it to humans. They breed in a variety of water containers and are often found around the home. Culex pipiens/restuans prefer water with high organic content, such as leaves, sticks and sewage effluent. Culex are most active at night and do not travel far from their breeding sites.

Culex pipiens

5. Anopheles

Of the mosquitoes trapped in Grey Bruce during the 2005 season, 1% were Anopheles punctipennis. Members of the Anopheles genus are known WNV vectors. They are vicious biters that most commonly breed in marshes with sufficient vegetation.

Anopheles punctipennis

Sources: Rutgers Entomology, South Dakota State University, Centers for Disease Control