HUMAN INDIVIDUALS VARY IN ATTRACTIVENESS FOR HOST-SEEKING BLACK FLIES(DIPTERA, SIMULIIDAE) BASED ON EXHALED CARBON-DIOXIDE

The attractiveness of 5 male subjects was compared to determine if fem ale black flies were attracted more readily by certain individuals and , if so, to determine the bases of such differences. During 2 yr, in e xperiments 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 attrac tiveness to approximate to 15% of previous levels and removed differen ces among subjects. Replacing breath exhalations with subject-specific CO2 levels restored subject attractiveness to approximate to 90% of o riginal 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 th e role of other breath components. A human form plus breath odor was m ore attractive than a human form and a human form plus body odor. Resu lts lend credibility to popular notions that some people are more attr active for black flies than are others and indicate that these differe nces may be accounted for by individual production rates of breath CO2 .