Anthropophilic black flies (Diptera:simuliidae) in the Amazon National Park (Tapajos) and their effects on man

Abstract

Six two-week excursions into the Amazon National Park (Tapajos) were made between August 1978 and August 1979 to study the biting patterns and seasonal abundance of anthropophilic black flies, as well as the flies' effects on the human population within the park. The only two man-biting species observed during this study were Simulium guianense and S. sanguineum s.l. Both species bite throughout the year in a bimodal pattern. That is, a morning peak is followed by a late-morning to mid-afternoon decline in biting activity, which in turn is followed by a second peak in late afternoon. The largest numbers of biting S. guianense were recorded at the height of the rainy season. Host-seeking S. sanguineum s.l., on the other hand, were most numerous at the beginning of the dry season. Of the various habitats studied, biting activity was most intense in partially cleared areas inhabited by humans near waterways, especially where streams and the Transamazon Highway intersected. These areas are probably attractive to the flies by virtue of their proximity to breeding sites and flyways. The presence of humans is not necessary, but it enhances the attractiveness of the areas to host-seeking Simulium. Biting activity was least intense in dense vegetation. Various allergic reactions were observed in individuals who had recently arrived at the park. Long-term residents, however, were extremely tolerant of numerous bites. Protective clothing and repellents are suggested for allergic individuals. The possibility of introducing Simulium-vectored filariases into currently unaffected areas, because of increased access to foci in other parts of Brazil, should not be overlooked.