The vertical distribution of flying mosquitoes (diptera, culicidae) in west african savanna

Abstract

The vertical distribution of mosquitoes was investigated at Keneba in The Gambia, using flight traps and suction traps set up over open ground. Flight traps were used to sample three levels, ground to 1*37 m, 1-45-2-82 m, and 2-90-4-27 m. Suction traps were mounted in two series of experiments at three levels, 0-68, 2-13 and 3-51 m, and in a third series at four levels, 0-91, 3-05, 6-10 and 9-15 m. Most species, including Anopheles melas Theo., A. squamosus Theo., Aedes punctothoracis (Theo.), the Culex decens group, C. tritaeniorhynchus Giles, Mansonia africana (Theo.) and M. uniformis (Theo.), were most common near the ground, with catches declining progressively with height. C. thalassius Theo. was frequent at all levels, although the largest catches were taken at 9-15 m. Only C. neavei Theo. and C. weschei Edw. were more common in the higher traps. Although larger catches of A. melas and C. tritaeniorhynchus were taken during moonless periods, the numbers of other species were unaffected by lunar phase. In general, the presence or absence of moonlight had little effect on vertical distribution. However, C. thalassius and the C. decens group were shown to be more attracted to flight traps in moonlight, and it is concluded that visual responses were involved. A limited series of four-level, human-bait catches, with the catchers stationed at the same heights as the suction traps of the third series, produced results similar to those of the suction trap collections.

Evaluation of the efficiency of bird-baited traps for sampling potential West Nile Fever mosquito vectors (Diptera: Culicidae) in Senegal

“…among the factors explaining the vertical dynamic of the mosquito vectors, the habitat of their host is probably the most important. indeed, Snow (1975) investigated the vertical distribution of mosquitoes in The Gambia and observed that zoophagic mosquitoes were mainly collected near the ground, ornithophilic mosquitoes in the canopy and mosquitoes feeding on mammals and birds at all levels. Contrary to a study conducted in California, showing an attraction and a feeding preference of Culex mosquitoes on chickens rather than pigeons (Reisen et al, 1992), our results indicated the preference of mosquitoes for pigeons instead of chickens at least for species of the Cx.…”

“…neavei group, were frequently collected at all levels between 0 and 6 m over open farmland in The Gambia (Gillies & Wilkes, 1976), at the ground-level in irrigated rice fields (Snow, 1979) and beyond 3 m height over open ground (Snow, 1975), while at Niakha it was mainly collected at the canopylevel (~ 3 m). Similarly to the observations made by Snow (1975) in The Gambia, our study found that Cx. poicilipes was common at all levels.…”

Sampling Adults with Non-attractant Traps

“…However, in later experiments, there were reduced catches of Anopheles melas in suction traps on moonlit nights, suggesting trap avoidance (Snow, 1982). Although ramp traps have been used in The Gambia to study mosquito flight levels and direction (Snow, 1975(Snow, 1976(Snow, , 1977Snow & Wilkes, 1977), it seems that at least some species respond visually to the traps. For example, the Culex decens group and Culex thalassius were commonly caught in ramp traps, whereas Anopheles melas tended to avoid them.…”

“…To study the vertical distribution of mosquitoes in a coastal area of The Gambia, Snow (1975) used the ramp traps of Gillies (1969) and Gillies & Wilkes (1972), and also 22·9-cm diameter 'Vent-Axia' suction traps. In five trials the ramp traps were set at heights of ground level-I·37 m, 0·69-2·06 m, 1-45-2·82 m, 2·13-3·51 m and 2·90-4·27 m, (Fig.…”

“…They concluded that trap catches are influenced by these visible cues (Bidlingmayer & Hem, 1979Bidlingmayer et ai., 1985). Similarly Snow (1975) believed that some, but not all, species of mosquitoes tended to avoid the much smaller 'Vent-Axia' suction traps he used in The Gambia. Bidlingmayer also considered that even moderate winds reduced the numbers of mosquitoes caught in his suction traps (Bidlingmayer, 1974;Bidlingmayer & Hem, 1980;Bidlingmayer et ai., 1985).…”