Molecular identification of blood meal sources in black flies (Diptera: Simuliidae) suspected as leucocytozoon vectors

Identification of the host blood meal of hematophagous insects can provide significant information regarding host preferences and the possibility of the transmission of disease agents. Currently, this knowledge is limited for black flies in the Oriental region. In this study, we used cytochrome b gene sequences for identification of blood meal sources of two black fly taxa, the Simulium asakoae complex and S. chumpornense Takaoka & Kuvangkadilok in Thailand. A total of 4,260 wild adult females were visually screened revealing 24 blood-engorged females from which cytochrome b was successfully amplified in 19 individuals. Comparisons in GenBank database revealed that all are closest to chicken (Gallus gallus) with sequence similarity of >98%. Therefore, these black fly species are feeding on chickens. We also molecularly investigated the hemosporidian blood protozoa genus Leucocytozoon in black flies and found 13 of 19 blood-engorged females positive for this protozoon. Sequence analysis revealed that this Leucocytozoon DNA could be assigned into two previously recognized groups, one with a Leucocytozoon reported from domestic chickens and black flies in Thailand, and another close to the L. schoutedeni. Our results indicate a high possibility that the S. asakoae complex and S. chumpornense are natural vectors of Leucocytozoon.

Molecular detection of Trypanosoma (Kinetoplastida: Trypanosomatidae) in black flies (Diptera: Simuliidae) from Thailand

Trypanosomes are parasitic flagellate protozoans that are important disease causing agents in humans and animals including economically significant livestock. Many blood-sucking insects are known to be vectors of trypanosomes but there is no data for the haematophagous black fly species in Asia. In this study, a molecular approach based on the small subunit ribosomal RNA (SSU rRNA) gene was used to detect trypanosomes in black flies from Thailand. A total of 470 wild-caught adult black flies representing nine morphological species were examined. Ten (2%) specimens of two ornithophilic black fly species, Simulium asakoae complex (n = 4) and S. chumpornense (n = 6), were positive for trypanosomes. The SSU rRNA sequences revealed that all trypanosome DNA found in black flies from Thailand is closely related to Trypanosoma avium with >99% sequence similarity. This is also supported by a phylogenetic analysis in which all trypanosomes from Thai black flies were resolved in the clade of T. avium. This is the first report for trypanosomes in Asian black flies and it is suspected that these insects are potential vectors of avian Trypanosoma.

A new species of black fly (Diptera: Simuliidae) in the Simulium (Simulium) multistriatum species-group from Thailand

A new black fly species of the Simulium multistriatum species-group of the subgenus Simulium Latreille is described from the mountainous area in northeastern Thailand, based on morphology and mitochondrial DNA sequences. The new species is morphologically similar to S. laui Takaoka and Sofian-Azirun and S. lacduongense Takaoka and Ya'cob originally described from Vietnam, S. fenestratum Edwards originally described from Indonesia and S. chaliowae Takaoka and Boonkemtong originally described from Thailand, but can be distinguished in the adult stage by the number of upper eye facets and globular shape of the spermatheca and in the pupal stage by the cocoon and shape of thoracic tubercles. Genetic distance and phylogenetic analyses of mitochondrial cytochrome c oxidase I sequences differentiated the new species from other members of S. multistriatum species-group. All specimens of the new species formed a monophyletic clade with strong support in all phylogenetic analyses. The minimum interspecific genetic distance of 4.9% is considerably greater than the new species maximum intraspecific genetic distance (2.7%).

DNA barcoding of human-biting black flies (Diptera: Simuliidae) in Thailand

Black flies (Diptera: Simuliidae) are important insect vectors and pests of humans and animals. Accurate identification, therefore, is important for control and management. In this study, we used mitochondrial cytochrome oxidase I (COI) barcoding sequences to test the efficiency of species identification for the human-biting black flies in Thailand. We used human-biting specimens because they enabled us to link information with previous studies involving the immature stages. Three black fly taxa, Simulium nodosum, S. nigrogilvum and S. doipuiense complex, were collected. The S. doipuiense complex was confirmed for the first time as having human-biting habits. The COI sequences revealed considerable genetic diversity in all three species. Comparisons to a COI sequence library of black flies in Thailand and in a public database indicated a high efficiency for specimen identification for S. nodosum and S. nigrogilvum, but this method was not successful for the S. doipuiense complex. Phylogenetic analyses revealed two divergent lineages in the S. doipuiense complex. Human-biting specimens formed a separate clade from other members of this complex. The results are consistent with the Barcoding Index Number System (BINs) analysis that found six BINs in the S. doipuiense complex. Further taxonomic work is needed to clarify the species status of these human-biting specimens.

Cytogenetic and Molecular Evidence of Additional Cryptic Diversity in High Elevation Black fly Simulium feuerborni (Diptera: Simuliidae) Populations in Southeast Asia

Simulium feuerborni Edwards is geographically widespread in Southeast Asia. Previous cytogenetic study in Thailand revealed that this species is a species complex composed of two cytoforms (A and B). In this study, we cytologically examined specimens obtained from the Cameron Highlands, Malaysia, and Puncak, Java, Indonesia. The results revealed two additional cytoforms (C and D) of S. feuerborni. Specimens from Malaysia represent cytoform C, differentiated from other cytoforms by a fixed chromosome inversion on the long arm of chromosome III (IIIL-5). High frequencies of the B chromosome (33-83%) were also observed in this cytoform. Specimens from Indonesia represent the cytoform D. This cytoform is differentiated from others by a fixed chromosome inversion difference on the long arm of chromosome II (IIL-4). Mitochondrial DNA sequences support genetic differentiation among cytoforms A, B, and C. The pairwise F(ST) values among these cytoforms were highly significantly consistent with the divergent lineages of the cytoforms in a median-joining haplotype network. However, a lack of the sympatric populations prevented us from testing the species status of the cytoforms.

Phylogeography of the black fly Simulium aureohirtum (Diptera: Simuliidae) in Thailand

The black fly Simulium aureohirtum Brunetti (Diptera: Simuliidae) is geographically widespread and utilizes diverse habitats. Previous studies revealed high genetic diversity, suggesting that this species could be a species complex. In this study, we used mitochondrial cytochrome c oxidase II sequences to examine genetic structure and demographic history of S. aureohirtum in Thailand. High level of genetic variation was observed due to the existence of genetically divergent lineages (A, B, and C). Lineages A and C were geographically widespread, while lineage B was geographically restricted to the eastern part of Thailand. The geographic localization of lineage B suggested limitations in gene flow, which is most likely a result of ecologically different habitats. Large genetic differences between individuals of lineages A and C, but geographically sympatric distributions of the members of these lineages, are considered to represent an admixture of the populations that have evolved allopatrically. Historical environmental change during the Pleistocene glaciations is possibly the factor that drove the lineage divergence. Population demographic history analyses revealed recent population expansions in the three lineages dating back to the last glaciations. These observations further highlight the significance of the Pleistocene climatic change on current genetic structure and diversity of living organisms of the Southeast Asian mainland.