DNA barcoding of tropical black flies (Diptera: Simuliidae) in Thailand: One decade of progress.

Black flies (Diptera: Simuliidae) are important blood sucking insects because they are the vectors of disease agents transmitted to human and other animals. Rapid and correct species identifications are necessary for all aspects of the study of black flies. DNA barcodes based on mitochondrial cytochrome c oxidase I (COI) have been effectively used for the determination of black fly species. However, the success of this method requires a large and reliable COI sequence library. In this study, 171 DNA barcoding sequences from 17 black fly species were added to NCBI GenBank database, six of these species were reported for the first time. Efficacy of DNA barcodes for species identification was examined using 1,286 sequences representing 89 nominal species of black flies in Thailand. A considerable level of success (90%) was achieved but efficiency of COI sequences for species identification was very low in the following species-groups; Simulium asakoae, S. feuerborni, S. multistriatum and S. striatum. Incomplete lineage sorting or inadequate variation of this genetic marker for differentiation of recently diverged species are the more likely explanations, and thus, more variable genetic markers are needed. Other reasons for unsuccessful DNA barcoding are imperfect taxonomy and the misidentification of sources of reference sequences. Because many new black fly species in Thailand were described recently, a reassessment of the COI sequences reported previously is necessary.