Biting activity of black flies in Guatemala: parity rates and differences between localities and habitats.

Host-seeking activity of anthropophilic black flies at 4 localities in Guatemala with different prevalence rates of onchocerciasis was assessed using human attractants and semimonthly catches over one year. Density of host-seeking Simulium ochraceum was greatest at the locality with the highest incidence of onchocerciasis and very reduced at the 2 localities with low levels of human infection. The overall percentage of parous host-seeking S. ochraceum at the 4 localities ranged from 41%-49%. Host-seeking activity appeared to be concentrated near streams containing immature stages, and few females dispersed as far as 3 km away. S. metallicum was the second most frequently captured species; however, at the locality with the highest prevalence of onchocerciasis, its host-seeking density was much less than that of S. ochraceum. For S. metallicum, the overall percentage of parous females ranged from 28%-34% at the 4 localities. S. metallicum were consistently taken in much greater numbers in coffee cultivation areas than in housing areas. Host-seeking S. callidum and S. gonzalezi also were captured.