NATURAL INFECTIONS WITH FILARIAL LARVAE IN TWO SPECIES OF BLACK FLIES (DIPTERA : SIMULIIDAE) IN NORTHERN THAILAND

To find out the natural infection with filarial larvae, female adult black flies were collected on a human attractant in December, 2001 at Tambol Ban Laung (altitude 750 m), Doi Inthanon National Park, in northern Thailand. The total number of females collected was 823 : of which 557 (67.7%) were identified as Simulium asakoae Takaoka et Davies, 144 (17.5%) as S. nigrogilvum Summers, 97 (11.8%) as S. nakhonense Takaoka et Suzuki and 25 (3%) as other six simuliid species. By dissections, eight third-and one second-stage larvae of unidentified filarial species were found in one of 138 S. nigrogilvum and one of 484 S. asakoae, respectively. Non-filarial nematodes were found in 1.03% (5/484) of S. asakoae. This is the first report of natural infections of two black-fly species, S. nigrogilvum and S. asakoae, with a filarial larva.