Sampling Adults with Carbon Dioxide Traps, Light-Traps, Visual Attraction Traps and Sound Traps

Abstract

As early as 1922 Rudolfs reported that carbon dioxide was an attractant for mosquitoes, and that carbon dioxide produced by breathing was an important factor in attracting mosquitoes to their hosts. Since then there have been differences of opinion as to whether carbon dioxide activates or orientates mosquitoes to hosts (Brown, 1951; Brown et al., 1951; Daykin et al., 1965; Hocking, 1963; Kahn & Maibach, 1966; Willis, 1947, etc.). Field trials by Gillies & Wilkes (1969, 1970, 1972, 1974) support the idea that carbon dioxide is an attractant. It is now generally accepted that carbon dioxide is, in concert with other olfactory cues, an attractant to virtually all haematophagous flies. In most of the West African species they studied, carbon dioxide was a middle range factor in host orientation, activating and attracting mosquitoes from about 15--30 m, but the actual distance depended on the species (Gillies & Wilkes, 1969). Ornithophagic species, however, appeared to be little attracted by carbon dioxide (Gillies & Wilkes, 1972). In later trials Gillies & Wilkes (1974), using ramp traps, found that whereas birds attracted Anopheles melas and Culex thalassius from at least 7 m, carbon dioxide (50 ml/min) attracted these ornithophagic species from up to only 4 m. But in Uganda Henderson et al. (1972) caught large numbers of ornithophagic mosquitoes in CDC light-traps when they were supplemented by dry ice, seemingly indicating that carbon dioxide was an important attractant. Different types of animals release different amounts of carbon dioxide. Roberts (1972) cited some interesting unpublished data supplied by P. W. Moe and H. F. Tyrrell on the rate of carbon dioxide produced by cattle. Fasted dairy cows produced an average of 1617 litres/24 hr, while lactating cows produced 5005 litres, `beef heifers' growing slowly 1727 litres and those on `full feed' 2639 litres carbon dioxide/24 hr. In contrast five small chickens released about 72 litres/ 24 hr (Gillies & Wilkes, 1974).