Chapters 1 - U.S. Fish and Wildlife Service

Refuge Resources
Culex tarsalis: This species is considered by most mosquito biologists to be the principal
encephalitis vector throughout much of its range in North America. It is Orange County’s
primary vector of western equine encephalitis and primary/secondary vector of St. Louis
encephalitis virus. Adults are active during the spring, winter, and fall. Though more common
in rural areas, the species has been found breeding throughout the county in association with
most types of clean, standing water sources.
Culex stigmatosoma: This close relative of Culex tarsalis breeds in stagnant or polluted
waters. Females are present throughout the County from spring to early fall. Although this
species seldom bites humans, it is an efficient vector of St. Louis encephalitis virus, and
therefore represents an important link in the maintenance of the disease in the area’s wildlife
populations.
Culex erythrothorax: The species has a distinctive reddish-color and is associated with coastal
and inland permanent wetlands. Though females do not disperse far (less than 1/4 mile) from
breeding sources to bite, their painful bite is usually followed by a severe local reaction. This
species has been found naturally infected with western equine encephalitis virus and St. Louis
encephalitis virus, but is considered an incompetent vector of either of these mosquito-borne
diseases. Laboratory tests have demonstrated this species to be an efficient vector of West
Nile virus.
Anopheles hermsi: This spring, summer, and fall mosquito is found sporadically throughout
the County in association with breeding sources containing floating mats of filamentous algae.
It is rarely found in salt marsh habitat. Although not a problem in Orange County at this time,
this species is known as a competent vector of malaria when the disease is present in an area.
Anopheles franciscanus: This species is rarely found in salt marsh habitat and only occurs in
limited numbers in Orange County. When present, it can be active during the spring, summer,
and fall. It breeds in water sources supporting abundant algal-growths and floating mats of
vegetation. This species seldom bites humans and does not experimentally transmit human
malaria in the laboratory.
Culiseta particeps: This species usually breeds during the cooler months of the year in shaded
algae-laden pools along foothill streams both inland and near the coast. This species is rarely
found in salt marsh habitat.
Ochlerotatus washinoi (formerly Oc. increpitus): This species occurs along the coast and
sporadically inland where it can be locally annoying to residents following wet winters. Larvae
develop in the upland portions of salt marshes and in floodwater sections of coastal and inland
streams. An annoying day biter, this species is more of a nuisance than a disease vector.
Culiseta inornata: This large, rust-colored winter mosquito is the most commonly
encountered mosquito during the cooler months of the year. Larvae develop in all types of
natural and man-made sources. Abundant larval populations occur in association with Aedes
squamiger in salt marsh habitats. At times, this species, which is known elsewhere to be a
vector for a number of mosquito-borne encephalitides viruses, can be locally annoying to
coastal residents.
Culiseta incidens: This cool weather species is most often encountered from February
through March and is found throughout the county in association with rainwater pools,
Draft Comprehensive Conservation Plan/Environmental Assessment 4-53