Age Composition and Vertical Distribution of Mosquito Populations in the Gambia, West Africa

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Abstract
The techniques of Polovodova and Detinova were used to determine the age composition of samples of Anopheles melas Theo. and Culex thalassius Theo. taken at different heights in savanna in the Gambia, West Africa. For both species the mean age of mosquitoes increased progressively with height. Similar trends were shown by flight and suction-trap collections of An. melas between ground level and 4.27 m, and by suctiontrap and biting catches up to 9.15 m for An. melas and Cx. thalassius . The age-grading data were combined with the results of vertical distribution studies with suction traps up to 9.15 m to estimate the relative numbers of mosquitoes in each age class at each height. It was concluded that the numbers of all age classes of An. melas declined with height, but this decrease was less marked for biparous and older insects, with the result that the proportion of older insects increased with height. A bimodal pattern of vertical distribution was shown by nulliparous and uniparous Cx. thalassius , with density maxima 0.91 and 9.15 m, while the absolute numbers of triparous and older insects increased with height.