Type: California Salt Marsh Mosquito
Scientific Name: Ochlerotatus
Habits (Adult Behavior)
Economic and Medical Importance
Ochlerotatus squamiger is commonly referred to as the California
Salt Marsh Mosquito because it breeds exclusively in the salt and brackish
marshes along the California coast. It is medium to large in size with a
grayish or black coloration. The end segments of the legs have broad white
bands. The mixture of dark and light scales on the wings gives them a
“salt and pepper” appearance.
This species breeds in
marsh waters following extra high tides or rains. It occurs only along the
Pacific Coast from Sonoma County to Baja California. It has been one of
the major problem mosquito species in the San Francisco Bay area within
the recorded history of the area.
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Mosquitoes have four distinct life stages: egg, larval, pupal, and adult
as seen in the illustration at the bottom. The female Oc. squamiger
deposits its eggs singly (up to 150) on the mud along the edge of receding
tide pools. The eggs remain unhatched until the next late fall or winter
rains and high tides. Eggs can remain viable for several years and not all
will hatch with the next flooding. After such marsh flooding, most eggs
may hatch into larvae (wigglers) within a short period of coming into
contact with water.
The larvae feed on small
organic particles and microorganisms suspended in the water. Feeding takes
place either at the bottom or near the water surface. Breathing takes
place at the water surface and is accomplished by means of orienting
upside-down with the tip of the tail (siphon) pointing up. At the end of
the larval stage, the mosquito molts and becomes a pupa (tumbler). The
pupa is active only if disturbed, for this is the “resting stage” when the
transformation from the larval stage to winged adult takes place. After
this transformation has been completed, the adult splits the pupal skin
Oc. squamiger is
usually single brooded, but two broods may occur under unusual climatic
conditions (i.e. El Nino conditions). The larval stage usually matures
during the winter and adults emerge from mid February to May. Adult
females may live up to three months.
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HABITS (ADULT BEHAVIOR)
Female Oc. squamiger are vicious biters, attacking man and other
mammals at any time of day, but maximum biting activity occurs at
twilight. They may bite actively at night indoors under lights, but
normally only bite outdoors. The females are strong fliers, migrating long
distances (up to 20 miles or more) in large numbers. Males do not bite,
instead they feed on nectar and plant juices. Females may also feed on
plant juices, but must obtain a blood meal in order to develop their eggs.
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ECONOMIC AND MEDICAL IMPORTANCE
This species has not been known to be commonly involved as a natural
vector of disease producing organisms in California. A limited number of
this species was found to be infected with West Nile virus during 2004.
The vicious biting habits of this species can render areas where it is
present virtually uninhabitable for man. Livestock can become agitated,
resulting in reduction in feeding and possible injury to frantic animals
attempting to escape severe attacks.
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PREVENTION AND CORRECTION:
The most important method of controlling salt marsh mosquitoes is to
eliminate or modify the specific areas in the salt marshes where the
larvae occur. This may be accomplished by circulation ditching, which
permits the water from very high tides or rains to flow back into the bay
The most commonly used biological control agent in mosquito control is the
mosquitofish (Gambusia affinis). Due to the salinity variance and
shallowness of many of the breeding sources for this mosquito, the use of
mosquitofish has not been feasible, and other biological control methods
have not been developed.
Problems with drainage or prevention may develop which can make it
necessary to use chemical control. Only trained mosquito and vector
control personnel should apply chemical control agents. Control agencies
have knowledge of the proper compounds and application techniques to
assure minimal environmental side effects.
It is important to remember
that chemical control provides only temporary relief and is used by
mosquito control agencies until other measures can be implemented.
Insect repellents may be
useful if it is necessary to be in an area where large numbers of these
adults are present. Always read and follow the directions on the label
carefully when using a repellent.
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