This species occurs throughout the Province from coastal islands to high mountains and from the 49th to 60th parallel. Hearle (1927c) thought he had found a new species, pacificensis, when he collected it on Discovery Island, noting a thick column of males swarming on a thinly wooded ridge near a salt marsh. Not very common in the Fraser Valley, it is one of the predominant species of the dry interior grasslands. Hearle (1932) found it, with campestris, the main pest in the Chilcotin. Most commonly it breeds in open grassy snow melt pools, but is also found in forests and is very abundant in river flood pools in the Rocky Mountain foothills. It is a strong flier, bites in broad daylight and is aggressive. Hearle observed it near Kamloops attacking livestock in some numbers in May and noted that cataphylla was a very productive breeder. This impression was verified by studies of Carpenter & Nielsen (1965) who found that one female could mature 5 batches of eggs in one season.
Controlling mosquitoes in pasture has always been a problem. Organchloride insecticides tend to accumulate in milk and fat, and carbamates and organophosphates, although not cumulative, are toxic to mammals. New bacterial insecticides, which are selective for mosquitoes, may prove to be an acceptable means of controlling larvae. Cattle can be protected from the adults with repellents and selectively toxic insecticides.
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