We found that intraspecific and interspecific genetic divergence overlaps for 7 of 13 species. Five of these species are not monophyletic. Several factors may explain species non-monophyly (Funk and Omland 2003), but incomplete
lineage sorting and imperfect taxonomy are probably among the most important for Gomphostilbiain Thailand. Simulium
asakoae and S. doisaketense are not monophyletic. One sample of each forms another lineage with 100% bootstrap
support. Deep divergence of this clade from the others suggests that it is a genetically distinct species.Simulium kuvangkadilokae is not monophyletic because it includes the sister species S. chumpornense; yet, these two species are
clearly differentiated morphologically. The geographic distributions of these species would seem to exclude the possibility of hybridization.Simulium kuvangkadilokaeis found in northeastern Thailand, whereas S. chumpornenseoccurs
in southern and western Thailand. The most likely explanation, therefore, is incomplete lineage sorting. Nonetheless,
imperfect taxonomy cannot be excluded because three hap