The biting midge Culicoides peregrinus Kieffer is a significant pest and vector species, and knowledge of its genetic diversity and genetic structure is critically important for designing an effective control program. However, such information is limited to only small sample-size DNA barcoding studies. Therefore, in this study, we used mitochondrial cytochrome c oxidase I (COI) to examine genetic structure and diversity of C. peregrinus from northeastern Thailand. In addition, we also inferred genetic relationships between C. peregrinus from Thailand and those reported from other countries across the geographic range of the species. Maximum intraspecific genetic divergence (3.83%) within Thai specimens was relatively high compared to other Culicoides species. Genetic structure analysis revealed that 71% (32 from 45) of population comparisons were highly significantly different. A high level of genetic structure among populations, even between those in close geographic proximity (22 km geographic distance) suggested that there has been little or no movement between local populations. This is possibly due to the ability to exploit diverse types of breeding site and a generalist feeding habit which enables C. peregrinus to complete its life cycle within cattle pens. Genetic relationships between Thai C. peregrinus and those reported from other countries revealed three genetically divergent lineages (A, B and C) associated with geographic origins. Specimens from Thailand + China formed lineage A, those from Australia formed lineage B and India + Bangladesh belonged to lineage C. These genetically divergent lineages also agree with morphological variation of the wing pale marking spots. Further investigation using independent genetic loci from nuclear genes will be very useful to resolve taxonomic status of these divergent lineages.
The deer fly (Diptera, Tabanidae), Chrysops dispar Fabricius is a common and widespread pest and vector species transmitting pathogens to animals including economically significant livestock. However, there is only limited information on genetic diversity, which crucial for understanding disease epidemiology. In this study, we examined genetic diversity of C. dispar collected from northeastern Thailand and compared with Indian material, from where this species was originally described. A molecular approach was used to screen for trypanosome. High genetic diversity was found within Thai C. dispar specimens with maximum 3.10% intraspecific genetic divergence due to the existence of two cryptic genetic lineages. Because these lineages coexist geographically, this indicates some degree of isolation, or the early stage of speciation. Phylogenetic analyses between Thai and Indian C. dispar populations revealed that they are genetically clearly distinct with minimum genetic divergence of 2.59%. A molecular species delimitation analysis supported that they belong to different species. Molecular screening of trypanosomes revealed that 20 of 90 specimens were positive and 16 of these were successfully sequenced. Based on sequence similarity, all were belonging to Trypanosoma theileri complex detected in cattle, the first report of this parasite in C. dispar. Phylogenetic analyses revealed that they belonged to two lineages (TthI and TthII) of this protozoa, corresponding to the occurrence of this parasite found in cattle in Thailand.
Mitochondrial cytochrome oxidase I (COI) sequences were used to determine the genetic diversity and species identification efficacy of Culicoides from Malaysia. In total, 100 COI sequences were obtained from 13 morphologically identified species. Intraspecific genetic divergence varied from 0.48 % in C. parahumeralis to 14.88 % in C. palpifer. However, most (8 of 13) had low (<3 %) intraspecific genetic divergence. Identification of these species based on best match (BM) and best close match (BCM) methods revealed a high efficiency of the COI sequences with 100 % and 99 % success for BM and BCM, respectively. Identification in the BOLD database revealed that 10 species were successfully determined and agreed with morphological identifications. There remained three taxa which were ambiguous (C. jacobsoni) or had no species level identity match (C. palpifer and C. flavescens). Phylogenetic analyses found that all Malaysian specimens were clustered with conspecifics except C. palpifer. Specimens of this taxon separated into two divergent clades, one with members of a BIN (BOLD:ADT9601) of C. palpifer whereas the other formed a novel genetic lineage. Molecular species delimitation identified the morphologically identified species of the Malaysian Culicoides in the respective species. The exceptions were two divergent lineages found in C. palpifer because they were treated as two different taxa. Molecular identification of the host blood meal source revealed that all were from water buffalo (Bubalus bubalis).