pdf, 57.71Mb - Entomological Society of Canada

Pest Status
Background
Chapter 6
Culex pipiens L., Northern House
Mosquito (Diptera: Culicidae)
1.A. GEORGE
The northern house mosquito, or rain barrel mosquito, Culex pipiens L., has long been
known to live in close proximity to humans in southern Ontario (Wood el al. 1979).
Larvae occur most commonly in stagnant water polluted to some degree with varying
amounts of decaying organic matter such as vegetation or sewage. C. pipiens larvae
are usually associated with, or follow the earlier occurring larvae of Culex resluans
Theobald. Adult populations of C. pipiens reach a peak in August, and though
breeding continues until October, females begin entering diapause in late August and
will not take a blood meal until the following spring (Madder el al. 1980, Madder 1981).
Mated females spend the winter in any protected shelter available to them. About mid­
May females seek their first blood meal and deposit the first egg rafts during the third
week of May at Guelph (Madder el al. 1980). Thoughfemales prefer the blood of birds
to that of mammals (Hayes 1961), they will, when abundant, invade homes and feed on
humans.
C. pipiens has been implicated in the spread of St. Louis encephalitis (SLE) and it,
along with Culex resluans (Madder el al. 1980), is assumed to be the vector of this
virus in eastern North America (Wood el al. 1979). The first recorded epidemic of SLE
occurred in southern Ontario in 1974-75 and stimulated investigations on surveillance
for,and abatement of this insect (Mahdy el al. 1979, Helson el al. 1980).
Four years (1977 -80) of identifying mosquito larvae by the author for the Middlesex­
London District Health Unit, London, Ontario survey crews, has helped to establish
catch basins, designed to drain away surface water, as major breeding sites for C.
pipiens in this area. In 1979 catch basins accounted for 96% of all breeding sites found
by the survey crew (Pringle el al. 1978). Moreover, on randomly selected streets in
Brampton, Clarkson, Streetsville, and Port Credit, 70% of the catch basins examined
contained Culex larvae (Hill, 1978, personal communication).
Catch basins not only provide water high in organic matter throughout the summer,
but, in addition, the underground pipes into which they drain provide ideal protected
sites for the females to spend the winter months. In addition, the street locations of
most catch basins puts them in close proximity to human dwellings. Finally, some
catch basins form a part of many farm drainage systems. These also support Culex
larvae. Thus, the drainage systems, established throughout southern Ontario to
remove surface water, provide ideal breeding conditions for C. pipiens and C.
resluans, the suspected vectors of SLE.
The planarian flatworm, Dugesia ligrina (Girard) (Tricladida, Turbellaria), has been
known to be a predator of mosquitoes since Lischetti (1919) reported it to consume
mosquito larvae (Jenkins 1964). A larger species, Dugesia dorolocephala (Woodworth),
has recently been shown also to act as an effective predator of mosquito eggs, larvae,
and pupae in California (Legner & Medved 1972, 1974, Medved & Legner 1974, Yu &
Legner 1976). Small Merosloma species, under 1 mm in length, of planaria in the order
Rhabdocoelida, kill mosquito larvae in the rice fields of California (Case & Washino
1979).
19