but does not always distinguish morphologically uniform species (Ilmonen et al. 2009). Our objective, therefore, is to assess the utility of DNA barcoding for Oriental black flies of the subgenus Gomphostilbia in Thailand. Simulium (Gomphostilbia) includes nearly 200 nominal species, about 10% of all described species of the Simuliidae (Adler and Crosskey 2010). In Thailand, 29 species of Gomphostilbia are known, with 24 formally named species and another 5 that are probably good species but undescribed. The species in Thailand are assigned to three species groups (batoense,
ceylonicum, and varicorne groups). One nominal species, Simulium siamense, is a complex of seven cytoforms, some
of which are probably valid species (Kuvangkadilok et al. 2008; Pramual and Wongpakam, unpublished data).