The vertical distribution of flying mosquitoes (Diptera: Culicidae) near an area of irrigated rice-fields in the Gambia

Abstract

The vertical distribution of flying mosquitoes beside an area of dry-season irrigated rice-fields was investigated at Bansang in the Gambia. Suction traps were set up at seven levels (0·1, 0·25, 0·5, 1·0, 2·1, 3·9 and 7·9 m) over a dry open field. Vertical distribution profiles were of two types. In the first, mosquito density decreased progressively with height and 80% or more of the total were taken below 1 m. Mosquitoes token included Anopheles gambiae Giles s. l., A. pharoensis Theo., Culex antennatus (Becker), C. ethiopicus Edw., C. neavei Theo. and Mansonia spp. Although the largest catches of A. rufipes (Gough) were taken in the lowest traps, this species Showed a tendency to a bimodal vertical distribution profile during. the early part of the night. In the second type, in which mosquitoes were frequent at all heights, C. poicilipes (Theo.) was the sole example. For the more common species at least, flight altitude declined with increasing wind speed. For a few categories of mosquitoes, flight levels decreased as the night progressed, but the presence of moonlight, or its absence, had no demonstrable effect.