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Mosquito Biology

 

     There over 3500 species of mosquitoes throughout the world with 150 of them residing in the United States.  In Illinois, there are over 55 species  with about 18 of them commonly caught in our of district. 

All mosquitoes found within the District's boundaries belong to one of two groups:  Floodwater mosquitoes or permanent and stagnant water mosquitoes.  Membership in one or the other group is dependent on the type of environment in which the female mosquito chooses to lay her eggs.

         FLOODWATER MOSQUITOES, such as Aedes vexans, lay their eggs on dry ground in areas that are subject to flooding following rainfall.  These eggs lay dormant until sufficient inundation occurs to initiate hatching.  Hatching is synchronized, and development from egg to a blood-feeding adult can occur within 7 to 10 days.  Areas within the District serving as production sources for such mosquitoes include swamp and marsh margins, roadside ditches, poorly maintained detention ponds and the floodplains of the Des Plaines River and associated creek systems.  Floodwater mosquito species are the most bothersome and prolific nuisance mosquitoes biting District residents during the daytime and nighttime.

        STAGNANT WATER MOSQUITOES lay their eggs directly on the water surface, either singly or in a cluster or raft.  The production sources are constantly replenished with the next generation's eggs, resulting in constant emergence of new adults during the course of the summer.  Human biting species occurring within the District include Coquillettidia perturbans, Anopheles punctipennis, and Anopheles quadrimaculatus.  More importantly, however, are species in the Culex pipiens complex, which are known to be competent vectors of Saint Louis Encephalitis, West Nile Virus and are believed to be responsible for both amplification of the virus in birds and transmission to man.  This District therefore places a high priority on the suppression of the members of this medically important group.

In order to survive all mosquitoes must have water to complete its life cycle.  Each species has its own preference for the type of water in needs.  Water quality can range from fresh rain water to sewage and mosquitoes will lay their eggs any where water is found (from plastic containers, tires to tree holes, edges of ponds & marshes).   Because they can exploit a variety of different aquatic habitats mosquitoes are very successful organisms.  Some are even adept at exploiting organically polluted water areas devoid of natural mosquito predators and parasites.

It is the female mosquito that bites humans and other animals (mammals, birds, reptiles and amphibians).  Males only feed on plant juices.  Females require a blood meal in order for her eggs to develop and be viable.  Some females prefer only one food source while others will feed on a variety food sources.

Mosquitoes undergo complete metamorphosis meaning they go through four stages (egg, larva, pupa, adult).  During the summer, mosquitoes typically go from egg to adult in 7-10 days but this will vary depending on temperature, humidity, and other environmental factors.  Males tend to live a very short time, usually about one week; and females live about one month again depending on environmental factors.  Below is a diagram of the mosquito life cycle with a description of life stage.                                                                                                         

Mosquito Morphology

Adult mosquitoes only have one pair of wings (forewings), the second pair of wings have been reduced to small organs called Halteres.  Halteres are used as balancing organs during flight.  The link below is diagram taken from Darsie and Ward, 1981.

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Adult anatomy

Mosquito larva and pupa complete their part of the life cycle in an aquatic environment.  They have adapted special structures to aid them.  The larvae have a siphon on their eighth segment which they use as a snorkel to gather air at the surface of the water.  The pupa have two structures coming off of the posterior region of the thorax called Trumpets.  These trumpets are used in the same manner as the siphons in the larval stage.  They also have "paddles" on the last segment of the abdomen which aid in swimming.

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Larval and pupal anatomy

The video below demonstrates the swimming behavior of larval mosquitoes.  It also shows two other invertebrates that might be mistaken for mosquito larva

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larva video

Mosquito Borne Diseases

One of the most important reasons for mosquito control is that mosquitoes are capable of transmitting diseases.  Diseases that are transmitted by insects and other arthropods are called Arboviruses.  These insects and arthropods that are capable of spreading diseases are called Vectors.  A few diseases that are transmitted by mosquitoes are listed below: 

Arboviruses

Worldwide

United States

Yellow Fever ~200,000 cases with 30,000 deaths each year rare in the United States
Dengue Fever 50-100 million cases each year.  Average case fatality rate is 5%                    100-200 cases each year - introduced to U.S. by travelers
St. Louis Encephalitis Worldwide distribution 4478 cases from 1964 - present - 3 to 30% fatality rate
Eastern Equine Encephalitis 200 cases from 1964 - present - 35% fatality rate
West Nile Virus ~9000 cases with 240 deaths in 2003

Non - Arboviruses

   
Malaria 300-500 million cases with more than 1 million deaths each year 1200 cases each year - most cases are immigrants and travelers from malaria risk areas
Dog Heartworm Worldwide distribution

Causes blockages in the heart and the vessels surrounding the heart in your dog and is treatable if diagnosed in time.

Occasssionally, heartworm can occur in humans with no known significance.  In the last 20 years, 80 cases have been reported from Florida.

You can find more in depth information about these diseases at the following website:

http://www.cdc.gov/ncidod/dvbid/