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A large mosquito with conspicuously spotted wings and indistinct pale bands on the tarsomeres; wing length 5.5-6 mm.
Proboscis and palps dark with scattered white scales. Pedicels brown, white-scaled on median surface. Scutum with several alternating dark and pale-scaled stripes in median area and with distinct middorsocentral spots of pale scales bordered by sparsely scaled posterior half-stripes. Abdominal tergites dark with basal bands of yellowish scales. Tarsomeres with very narrow basal and apical bands, indistinct on forelegs. Wing scales dark, aggregated into distinctive clusters on vein Rs and at bases of R2, R3, M1 and M2. Crossveins bare, in line with each other.
Antennae short, with few spicules. Head seta 5-C 5 or more branched and shorter than the 2 to 4-branched 6-C. More than 40 slipper-shaped comb scales in a patch. Siphon 3 x 1, a short pecten is followed by a row of setae reaching apical ¼. 1-S many-branched, inserted basally within pecten. Saddle surrounding anal segment. 1-X fine, shorter than saddle.
Culiseta, a feminine diminutive of the masculine Culex (ancient Romans did not sex their mosquitoes) was used to separate the species we now know as impatiens from the genus Culex. The name, Theobaldia, was used by several authors until it was found to be invalid having already been used for a genus of Molluscs.
Culiseta females have short palps and a trilobed scutellum and the blunt abdomen resembles that of Anopheles, Culex and Mansonia. Some of our species have patches of dark scales on the wings similar to those of anophelines. Dubious specimens will have to be examined for the presence of prespiracular and absence of postspircular setae.
The single pair of branched setae (1-S) at the base of the siphon characterizes larvae of this genus.
The pupae are difficult to distinguish with certainty from those of other genera. Most collectors will keep them until the adults emerge.
Most Culiseta species in our Province lay their eggs in rafts on water surfaces. Cs. morsitans, however, lays egg rafts on vegetation at the margin of its breeding sites. If the eggs are washed down into the water some may hatch and larvae may overwinter in the benthic debris. If not washed down, the eggs probably overwinter and hatch like those of aedines when flooded in the spring. Most Culiseta species overwinter as fertilized, and probably blood-fed, females and at least some species can produce several generations each year.
In 1932, Hearle wrote "This is the most widespread and commonest species in B.C." It is a domestic mosquito and in the 1920s almost every rain water barrel in the Lower Mainland was teeming with its larvae throughout the summer (Hearle 1921). Its larvae are still found in artificial containers, ditches, garden, woodland and polluted pools and in brackish coastal pools where they are often associated with Ae. togoi and occasionally with Ae. dorsalis larvae. The females hibernate, reappearing in early spring, when partly on account of their large size, they cause consternation out of all proportion to their importance. For reasons that are not clear at present, populations of this species are greater in spring and fall than at the height of summer, although there are several broods each season. Females are not usually aggressive biters and take blood from large mammals more often than from man. I have, however, noticed a temperature effect in the Lower Mainland where this species readily bites humans on warm evenings (above 20°C).
"This species is our commonest mosquito with many generations a year and [is] very well adapted to domestic sites. It has recently been found with West Nile Virus (WNv) (CDC 2005) and in laboratory tests it transmitted WNv and several other viruses (Reisen et al. 2006)" (Belton 2007, with permission). Although it can transmit WNv, it is not a highly competent vector (Belton 2007).
Belton, Peter. 2007.British Columbia mosquitoes as vectors of West Nile virus.Peter Belton web site. Simon Fraser University.
Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2021. E-Fauna BC:
Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab
for Advanced Spatial Analysis, Department of Geography, University of British
Columbia, Vancouver. [Accessed:
2022-01-16 8:32:04 PM]
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