Human individuals vary in attractiveness for host-seeking black flies (Diptera: Simuliidae) based on exhaled carbon...

The attractiveness of 5 male subjects was compared to determine if female black flies were attracted more readily by certain individuals and, if so, to determine the bases of such differences. During 2 yr, in experiments contrasting different groupings of the subjects, 1 subject was consistently the most attractive, whereas another was consistently the least attractive. Attractiveness of the remaining 3 subjects was intermediate. Removing exhaled breath resulted in a decrease of attractiveness to approximately 15% of previous levels and removed differences among subjects. Replacing breath exhalations with subject-specific CO2 levels restored subject attractiveness to approximately 90% of original levels. Exhaled breath from which CO2 had been removed with a soda-lime filter and then augmented with bottled CO2 was consistently more attractive than CO2 alone at the augmentation rate, indicating the role of other breath components. A human form plus breath odor was more attractive than a human form and a human form plus body odor. Results lend credibility to popular notions that some people are more attractive for black flies than are others and indicate that these differences may be accounted for by individual production rates of breath CO2.