Mosquitoes (Order Diptera, Family Culicidae) are some of the most adaptable
and successful insects on earth and are found in some extraordinary places.
Virtually any natural or man-made collection of water can support mosquito
production. They've been discovered in mines nearly a mile below the surface,
and on mountain peaks at 14,000 feet, and if you know where to look, there is a
good possibility that there are mosquitoes breeding in your own backyard. Not
every species of mosquito causes problems for man, but many have profound
effects. Mosquitoes can be distinguished easily from other flies by the fact
that they have both a long, piercing proboscis and scales on the veins of their
wings. Approximately 167 species of mosquitoes belonging to 13 genera are found
in the United States, with only about 50 different species found in
Colorado. Only a few of these are important as carriers of disease, but many
more are important as nuisances.
There are approximately forty two different species of mosquitoes found in
the State of Colorado, and of all of the different types, around 90% of the
adult mosquito population along the Front Range is made up of two species,
depending upon habitat. The first, and most vicious biter, is the
"floodwater" mosquito, Aedes vexans. This mosquito and other closely
related floodwater species are responsible for nearly all severe outdoor
annoyance in Colorado. The second, an important disease vector, is Culex tarsalis. These two
species, although very different in their life-styles, have one thing in common,
and with all mosquito species. They must have water for their early stages, and
all undergo the same four-stage life cycle: egg, larva, pupa, and adult. The
larval and pupal stages are always aquatic.
Depending on the particular species, the female mosquito lays
her eggs either individually or in attached groups called rafts. The eggs are
placed either directly on the surface of still water, along its edges, in
treeholes, or other areas that are prone to flooding from rain, irrigation or
overflow. In some species, the eggs may hatch within a few days of being laid,
with the exact amount of time dependent on temperature. But if the egg is laid
out of water and is subject to intermittent flooding, the embryo may lay dormant
for several years until the ideal natural hatching conditions are met.
Mosquitoes frequently overwinter in the egg stage, but may also overwinter as
larvae or adults.
|The Larval Stage
Once the egg hatches, the larval stage begins. The larvae of most mosquito
species hang suspended from the water surface. An air tube extends from the
larva's posterior to the water surface and acts as a snorkel. The larvae
filter-feed on aquatic microorganisms near the surface. As a defense mechanism,
when alarmed, the larvae can dive deeper into the water by swimming in a
characteristic "S" motion. As they feed, larvae outgrow their exterior
covering and form a new larger skin, casting off the old ones. The stages
between these molts are called instars. The larval stage has four instars. The
length of the larval stage ranges from 4 to 14 days, varying with species, water
temperature, and food availability.
In the pupal stage, no feeding occurs. But like the larva, the pupa is sensitive to light, shadows and other water disturbances. Pupae are also
physically active and employ a tumbling action to escape to deeper water. The
pupal stage lasts from 1 1/2 to 4 days, after which the pupa's skin splits along
the back allowing the newly formed adult to slowly emerge and rest on the water
The male mosquito will usually emerge first and will linger
near the breeding site, waiting for the females. Mating occurs quickly after
emergence due to high adult mortality rates. As much as 30% of the adult
population can die per day. The females compensate for this high rate by laying
large numbers of eggs to assure the continuation of the species. Male mosquitoes
will live only 6 or 7 days on average, feeding primarily on plant nectars.
Females with an adequate food supply can live up to 5 months, while the average
female survives about 6 weeks. To nourish and develop her eggs, the female
usually must take a blood meal in addition to plant nectars. She locates her
victims by the carbon dioxide and other trace chemicals exhaled, and the
temperature patterns they produce. Mosquitoes are highly sensitive to several
chemicals including carbon dioxide, amino acids, and octenol. The average female
mosquitoes flight range is normally between 1 and 10 miles, but some species can
travel up to 40 miles before taking a blood meal. After each blood meal, the
female will oviposit (lay) her eggs, completing the life cycle. Several
ovipositions per female are possible.
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