Number of generations, egg production, and developmental time of Culex pipiens and Culex restauns (Diptera: Culicidae) in southern Ontario.

Abstract

Culex pipiens and Cidex restuans each had 3 major generations per year during 1978, 1979, and 1980 in southern Ontario, Canada. Eggs of the 1st generation were laid from mid-May to mid-June, the 2nd from mid-June to mid-July, and the 3rd from mid-July to early August. A small 4th generation occurred during August. The 3rd generation of Cx. pipiens and the 2nd of Cx. restuans were usually the largest. Overwintered females of Cx. pipiens and Cx. restuans produced fewer eggs per raft than females of the summer generations, although egg production declined in late summer. Temperature during ovarian development did not affect egg production; however, the development of Cx. pipiens larvae at high densities reduced egg production. The rates of embryonic, larval and pupal development were correlated positively with temperature, although larval and pupal development was negatively correlated with larval density. Water temperature was more important than density in influencing the developmental rate of Cx. pipiens larvae, although the opposite was true with Cx. restuans . Survival of larvae and pupae of each species was similar and depended on larval density and not temperature. Based on biological and epidemiological factors, the most efficient procedure to reduce the possibility of an outbreak of St. Louis encephalitis in Ontario is larval control from late May through July.