Behavioural and phenological studies of woodland mosquitoes in the Winnipeg area

Abstract

A study was carried out in the woodlands of Charleswood and Fort Whyte within Winnipeg, to determine whether these areas contribute to Winnipeg's pest mosquito populations. The species compositon, density and seasonal abundance of larvae were monitored throughout the 1973 season. Snow-melt flooding of woodland pools was minimal in 1973 which greatly reduced the spring, univoltine species production. Heavy precipitation throughout the season reflooded some of these pools and produced broods of multivoltine Aedes. The seasonal succession and abundance of woodland adult mosquitoes was monitored using weekly CO2-baited traps and 10 minute biting-counts, throughout the 1972 and 1973 mosquito seasons. During 1972, spring univoltine species accounted for the major annoyance during late May and early June. During 1973, maximum trap catches were recorded in mid-July and consisted almost entirely of Aedes vexans. The occurrence of multivoltine Aedes was found to be dependent on the intensity and duration of summer rainfall. Although few A. vexans were produced in the woodland areas this species does appear to seek shelter there during the day. Thermal fogging with 5% Malathion proved unsuccessful in reducing mosquito populations in a wooded area along the La Salle River. A. vexans was shown to display a crepuscular activity rhythm which is probably initiated by the changing light intensities at dusk and dawn. Temperature and wind were shown to limit the nocturnal activity of A. vexans.