The effect of a reduction in expired carbon dioxide on the attractiveness of human subjects to mosquitoes

Abstract

The attractiveness, to mosquitoes, of human subjects breathing normally and wearing a breathing apparatus which removed 95·5% of expired carbon dioxide were compared in the field. Significantly fewer mosquitoes approached the subject with a reduced carbon-dioxide output. Species differences were apparent in the degree of reduction of mosquitoes at the bait, as measured by the ratio of numbers attracted to subjects without and with the breathing apparatus. From the results of trials in the Gambia, West Africa, this ratio gave values of 0·67 for Mansonioides spp., 0·46 for Anopheles gambiae Giles/A. melas Theo. and 0·19 for Culex thalassius Theo., while complementary work in southern England gave a value of 0·34 for Aedes cantans (Mg.)/Ae. annulipes (Mg.). A reduced carbon-dioxide output had no effect on the proportion of mosquitoes attempting to feed once within close range of the host. These findings confirm that carbon dioxide is a long- or medium-range attractant.