Culex tarsalis

Geographic Range

Culex tarsalis is a North American species of mosquito that occupies a large swath of territory between northern Mexico and southern Canada, spreading from the Pacific to the Atlantic coast. It is most commonly seen in California, at elevations ranging as high as 3000 meters. The species is much less abundant in areas east of the Mississippi River, although there have been several reported cases of C. tarsalis occurrences as far as New Jersey, which were found exploiting freshwater impoundments constructed to eliminate the salt marsh species Aedes sollicitans .

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

This species can be found in almost every environment in the U.S. The spread of C. tarsalis across the U.S. has been facilitated by human activity, with irrigation making formerly inhospitable arid regions available for breeding, which can occur in any sunlit standing freshwater. The species has been found at elevations ranging from sea level to over 3000 meters. Larval habitats are often shared with Culiseta inornata , Culex quinquefasciatus , Culex salinarius , Culex pipiens , and Culex stigmatosoma , as well as a number of species of Aedes and Anopheles . Although a widespread and hardy species, C. tarsalis was not able to establish a large presence in the Northeast due to competition from C. salinarius .

• Habitat Regions
• temperate temperate
• terrestrial terrestrial
• freshwater freshwater

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• forest forest
• mountains mountains

• Aquatic Biomes
• lakes and ponds

• Other Habitat Features
• agricultural agricultural

Physical Description

Culex tarsalis is a black mosquito distinguished by a white band on its proboscis, as well as white bands on its tarsal joints. It also has white longitudinal stripes extending along the middle and hind legs, and dark chevron patterns along the underside of its abdominal segments.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

Development

Developmental periods range from 7 days to almost four weeks, depending upon temperature and food availability. Larvea and pupae live in the water, and emerge as adults into the air.

• Development - Life Cycle
• metamorphosis metamorphosis

Reproduction

Females oviposit egg rafts conataining an avaerage of about 190 eggs in newly flooded, freshwater substrates, larvae exploiting microfloral blooms produced by the release of nutrients from decomposing vegetation. It was found that larval populations declined markedly 2-3 weeks after habitat flooding due to a reduction in these blooms. Typical developmental sites vary in size from small man-made containers to large ponds. In general, C. tarsalis will breed in water in any sunny location, and will tolerate a wide range of water conditions. Developmental periods range from 7 days to almost four weeks, depending upon temperature and food availability. Females spend the winter carrying inseminated nullipars (undeveloped eggs) which require a blood meal to mature in the spring. However, in a phenomenon termed autogeny, some females are able to mature their initial egg batch without a blood meal, and oviposit 4-5 days after emergence.

Females lay eggs in a "raft" that floats on top of the water. Each raft contains about 190 eggs. Females prefer to lay their eggs in newly flooded areas, so nutrients are available for larvae to eat. Females will lay their eggs in all types of wet areas, from small containers of standing water to large ponds. Females spend the winter carrying undeveloped eggs. Once they feed on blood the next spring, their eggs can finish developing, and can be laid.

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous

Beyond developing eggs, and laying them in an appropriate habitat, females do not provide parental care.

• Parental Investment
• pre-fertilization
  • provisioning

Behavior

Culex tarsalis is most active in the few hours after sunset, parasitizing both bird and mammal hosts. Host specificity is quite catholic, and adjusts to changes in host availability. During the daytime, adults can be found resting in shaded areas such as tree cavities and animal burrows. Culex tarsalis has been recorded to disperse up to 27 kilometers on host-seeking flights, averaging about 90 meters per day.

• Key Behaviors
• flies
• nocturnal nocturnal
• parasite parasite
• motile motile
• hibernation hibernation

Communication and Perception

These mosquitoes find hosts by detecting the sweat and carbon dioxide exhaled by mammamls or birds.

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

Culex tarsalis exhibits relatively generalized (catholic) blood feeding patterns, feeding on both birds and mammals, depending on host availability and distribution. When populations are low in the spring, most females tend to feed on birds . In the late summer when abundances are higher, birds will learn to avoid these mosquitoes, causing C. tarsalis to seek mammalian hosts, including rabbits , horses , cattle , and humans . This seasonal shift may be a significant factor in zoonotic viral transmission. In general, C. tarsalis shows a preference for bird hosts over mammals at a ratio of approximately 3:1.

Both sexes also feed on nectar and plant fluids.

• Primary Diet
• carnivore carnivore
  • sanguivore sanguivore
• herbivore herbivore
  • nectarivore nectarivore

• Animal Foods
• blood

• Plant Foods
• nectar
• sap or other plant fluids

Predation

Bats and birds are known to eat mosquitoes.

Ecosystem Roles

These mosquitoes transmit St. Louis Encephalitis and Western Equine Encephalitis. They are a nuisance to many species of birds and mammals. They also may be prey for birds and bats. Because adults eat nectar, they may pollinate some plant species.

• Ecosystem Impact
• pollinates
• parasite parasite

Economic Importance for Humans: Negative

Culex tarsalis is one of the most important vectors of arboviruses in North America, most noted for the transmission of St. Louis Encephalitis (SLE) and Western Equine Encephalitis (WEE). Both are zoonotic diseases maintained in natural bird reservoirs. Some mammals, particularly jackrabbits , may be involved in transmission cycles in certain areas. SLE, sometimes called "sleeping sickness" or "summer flu," is associated with aseptic meningitis and inflammation of brain tissue and can be fatal in humans, usually among children or the elderly, with a mortality rate of up to 23%. WEE is less virulent in humans, with a mortality rate of about 4%; however, it is a serious disease in horses and can impose a heavy economic cost in lost livestock and vaccination and mosquito control programs. Human infections are most common in the warmer months, especially toward the end of summer as C. tarsalis begins to seek mammalian hosts. Transmission rates are also affected by temperature.

Culex tarsalis has also been observed to be a vector for the Llano Seco, Turlock, Gay Lodge, and Hart Park viruses, as well as several species of avian malaria. In laboratory experiments, C. tarsalis was found to be a competent vector of Japanese and Venezuelan Equine Encephalitis viruses.

• Negative Impacts
• injures humans
  • carries human disease
• causes or carries domestic animal disease causes or carries domestic animal disease

Conservation Status

This species is extremely abundant in many places and in no need of special protections.

Additional Links

Encyclopedia of Life

Contributors

Matthew Wund (editor), University of Michigan-Ann Arbor.

Raymond Pahk (author), University of Michigan-Ann Arbor, Solomon David (editor), University of Michigan-Ann Arbor.

References

Crans, W., L. McCuiston. 1987. Rare New Jersey mosquito species collected in 1986. Proc. N. J. Mosquito Control Assoc. , p: 89-94.

Noden, B., C. Pumpuni, J. Vaughan, J. Beier. 1995. Noninfectious sporozoites in the salivary glands of a minimally susceptible anopheline mosquito. Journal of Parasitology , 81: 912-915.

Reisen, W., R. Meyer, S. Presser, J. Hardy. 1993. Effect of temperature on the transmission of western equine encephalomyelitis and St. Louis encephalitis viruses by Culex tarsalis (Diptera: Culicidae). Journal of Medical Entomology , 30, no. 1: 151-160.

Reisen, W. 1993. The Western Encephalitis mosquito, Culex tarsalis. Wing Beats , 4 (2): 16.

Rejmankova, E., M. Rejmanek, M. Pitcairn, R. Washino. 1988. Aquatic vegetation in rice fields as a habitat for Culex tarsalis and Anopheles freeborni. Proceedings and papers of the annual conference of the California Mosquito and Vector Control Association , 56: 160-163.

Walton, W., N. Tietze, M. Mulla. 1990. Ecology of Culex tarsalis (Diptera: Culicidae): factors influencing larval abundance in mesocosms in southern California. Journal of Medical Entomology , 27: 57-67.

Wekesa, J., B. Yuval, R. Washino, A. Vasquez. 1997. Blood feeding patterns of Anopheles freeborni and Culex tarsalis (Diptera: Culicidae): effects of habitat and host abundance. Bulletin of Entomological Research , 87: 633-641.