Mosquito Biology
Larvae
All mosquitoes start their life cycle in the water. Some species prefer salt or brackish water as found in our local coastal saltmarshes while others prefer fresh water derived from rainfall or agricultural irrigation. Mosquitoes do not develop in running water or in deep waters such as our Indian River Lagoon, lakes, or ponds.
The mosquito life cycle begins with an egg. After maturing for a few days, a mosquito egg may enter a “waiting period” where it is metabolically inactive. Some eggs may wait for a year or more for ideal hatching conditions, though most hatch within days or weeks. This “reserve” of unhatched eggs means that simply killing all the mosquito larvae in an area does not guarantee that it will not produce larvae again. This is particularly true of our local saltmarsh species.
Some freshwater mosquitoes lay their eggs in a floating mass called a “raft” on the surface of the water. Others may place their eggs singly at the water line in small containers. Our saltmarsh mosquitoes lay their eggs one at a time on the damp soil of the marsh, not on the water itself. By keeping these marshes covered with a thin layer of water, their life cycle can be interrupted. See our section on salt marshes for more about “source reduction”.
Mosquito eggs hatch when they are exposed to water. In citrus groves, different species may lay their eggs at different levels within the irrigation swales. A little rain which floods only the bottom of the swale will hatch one species while a heavy rain or flood irrigation event which completely fills the swales will hatch all species. The Psorophora howardii mosquito lays its eggs high in the swales. Once they hatch, the larvae actually eat those of other mosquito species. This is not a mosquito control answer in itself since P. howardii is itself a very large and annoying mosquito.
In the high salt marshes, rainfall or an unusually high tide will flood the area. Most mosquito eggs waiting in the soil will hatch quickly, some within minutes.
Larval Development
All mosquitoes have a six-part development in the water (egg, 4 larval stages, pupal stage). After the egg hatches, the larvae begin to feed on suspended organic matter. Each larva will go through four distinct moltings called “instars” where it sheds its outer covering and emerges larger and more mature. During the summer months, each instar takes about one day. Cool weather can lengthen the time of larval development though it will take near freezing temperatures to actually kill the larvae once they have hatched. The final aquatic stage is a pupae. It is in this stage that the mosquito metamorphizes into the adult, flying form. The pupal stage can take two days or less.
The threat to mosquito larvae is that their aquatic habitat will dry out before they can complete this part of their life cycle. It is assumed that female mosquitoes can detect which spots are likely to stay wet for a week or so and lay their eggs in these locations.
Mosquito larvae breath air. Some, as in the image above, have a special breathing tube which they thrust through the surface layer of the water. Other species lack the specialized tube and must lie parallel to the water surface to breath. When disturbed or when seeking food, the larvae may sink briefly to the bottom of the water, but they must soon rise again for air.
After a couple of days as a pupa, the pupal case splits open and a fully developed adult mosquito emerges.
See our section on mosquito larvicides for larval control information.
Adult Mosquitoes
The male mosquitoes typically emerge before the females. Newly emerged mosquitoes will rest for several hours, allowing their wings to inflate into shape and harden. Soon after, they mate. Only the female mosquito bites using blood protein for the development of eggs. Depending on the mosquito species, humans and other mammals, reptiles, and birds are hosts, serving as sources of blood. The female is capable of producing hundreds of fertile eggs. Some mosquito species can lay a limited number of eggs without needing blood. This is called “autogeny” and this mechanism allows the species to survive even under adverse conditions.
The males are not as large or as hardy as the females and in the wild will die within a few days to a week. During their brief life, nectar is their only food source. Female mosquitoes also use nectar for their energy needs.
How Mosquitoes Find You
Mosquitoes find a host by several mechanisms. The primary attractants for mosquitoes are the carbon dioxide and lactic acid produced by animals. It appears that at least some species can also identify various hosts by visual means. Other chemical vapors also interest mosquitoes, such as octanol found in the breath of cows.
There have been claims that eating particular foods may make humans more attractive or less attractive to mosquitoes. Studies have not proven these claims to be true, so hold the garlic …
Sounds do not seem to have any relevance when it comes to seeking a host for blood-feeding … regardless of the advertised claims of “ultrasonic mosquito repeller” devices. Studies have not found “bug zapper” products to significantly reduce mosquito numbers.
Mosquito Repellants
The chemical-detection methods of mosquitoes can be confused by repellants. Many commercial mosquito repellants contain “DEET” in various concentrations. Other repellants on the market include those with picaridin and oil of eucalyptus.
Regardless of the repellant used, always follow the label directions.