The vertical distribution of some West African mosquitoes (Diptera, Culicidae) over open farmland in a freshwater area of the Gambia

Abstract

Mosquitoes flying at low levels over open farmland were sampled by means of electrical suction traps. These were set up at nine levels from ground level up to 6 m. From the vertical profiles obtained it was possible to recognise three patterns of behaviour: (1) a low-flying group with relatively very high densities below 1 m, comprisingMansonia (Man-sonioides)spp.,Aedesspp. and some species ofAnopheles; (2) an intermediate group with densities rather evenly distributed at the lower levels but declining above 2–4 m, comprisingA. funestusGiles,A. gambiaeGiles andCulex neaveiTheo.; (3) a high-flying group with catches at 6 m greater, or much greater, than at 1 m, composed ofC. antennatus(Becker),C. thalassiusTheo. andC. poicilipes(Theo.). For all species, catches after 23.00 h showed an increase in the proportion of mosquitoes taken in traps at the lower levels, this being most marked at ground level and 0·5 m. No influence of either moonlight or wind speed could be detected to account for this. Biting catches on human baits showed a generally similar pattern to suction-trap catches, although differences between baits at 1-m intervals at the higher levels were less than with unbaited traps.