Biting midges of the genus Culicoides Latreille are significant pests and vectors that transmit pathogens to humans and other animals. Cattle are among the important livestock that can potentially be severely affected by Culicoides. In this study, we examined the species diversity, abundance, and host blood meal identification of biting midges in cattle pens located in three different land use types: villages, agricultural areas, and the forest edge. A total of 12,916 biting midges were collected, and most of these were from cattle pens located in villages (34%) and agricultural land (52%). Morphological identification revealed 29 Culicoides species. The most common species were C. oxystoma, C. mahasarakhamense, C. peregrinus, and C. shortti; taken together, these species represented >80% of all specimens collected. Despite midges being less numerous (14% of the total collection), cattle pens located near the forest showed greater diversity (23) than those from villages and agricultural areas. More diverse immature habitats and host blood sources from wildlife in nearby forests possibly explain the greater diversity in the cattle pens near the forest edge. Host blood meal analysis revealed that most (65%) biting midges had fed on buffalo despite the fact that this animal was much less numerous than cows or chickens. Relatively larger size and black-colored skin could be factors that make buffalo more attractive to biting midges than other host species. In this study, we also provided 67 DNA barcoding sequences of 13 species, three of which (C. flaviscutatus, C. geminus, and C. suzukii) were first reported from Thai specimens. DNA barcode analysis indicated cryptic diversity within C. hegneri and C. flavescens in Thailand, and thus, further investigation is required to resolve their species status.

Understanding the factors associated with the species diversity and distribution of insect vectors is critically important for disease epidemiology. Black flies (Diptera: Simuliidae) are significant hematophagous insects, as many species are pests and vectors that transmit pathogens to humans and other animals. Ecological factors associated with black fly species distribution have been extensively examined for the immature stages but are far less well explored for the adult stage. In this study, we collected a total of 7706 adult black fly specimens from various locations in forests, villages and animal shelters in Thailand. The integration of morphology and DNA barcoding revealed 16 black fly taxa, including Simulium yvonneae, a species first found in Vietnam, which is a new record for Thailand. The most abundant species was the Simulium asakoae complex (n = 5739, 74%), followed by S. chumpornense Takaoka and Kuvangkadilok (n = 1232, 16%). The Simulium asakoae complex was dominant in forest (3786 of 4456; 85%) and village (1774 of 2077; 85%) habitats, while S. chumpornense predominated (857 of 1175; 73%) in animal shelter areas. The Simulium asakoae complex and S. nigrogilvum Summers, which are significant pests and vectors in Thailand, occurred at a wide range of elevations, although the latter species was found mainly in high (>1000 m) mountain areas. Simulium chumpornense, S. nodosum Puri and the S. siamense Takaoka and Suzuki complex occurred predominately in low (1000 m) mountain areas. A host blood meal analysis revealed that the S. asakoae; S. chamlongi Takaoka and Suzuki; S. nigrogilvum; S. chumpornense; and the S. striatum species group were biting humans. This is the first report of the latter two species biting humans. We also found that S. chumpornense was biting turkeys, and S. chamlongi was biting chickens, which are new host blood sources recorded for these species. In addition, we found that the S. feuerborni Edwards complex was biting water buffalo, which is the first report on the biting habits of this species.

Biting midges of the genus Culicoides Latreille are significant pests and vectors of disease agents transmitted to humans and other animals. Understanding the genetic structure and diversity of these insects is crucial for effective control programs. This study examined the genetic diversity, genetic structure, and demographic history of Culicoides mahasarakhamense, a possible vector of avian haemosporidian parasites and Leishmania martiniquensis, in Thailand. The star-like shape of the median joining haplotype network, a unimodal mismatch distribution, and significant negative values for Tajima’s D and Fu’s F_S tests indicated that populations had undergone recent expansion. Population expansion time was estimated to be 2000–22,000 years ago. Population expansion may have been triggered by climatic amelioration from cold/dry to warm/humid conditions at the end of the last glaciations, resulting in the increased availability of host blood sources. Population pairwise F_ST revealed that most (87%) comparisons were not genetically different, most likely due to a shared recent history. The exception to the generally low level of genetic structuring is a population from the northern region that is genetically highly different from others. Population isolation in the past and the limitation of ongoing gene flows due to large geographic distance separation are possible explanations for genetic differentiation.

Genetic diversity and ecology are two important aspects of vector species crucial to a full understanding of disease epidemiology. In this study, we examined genetic diversity, genetic structure and the physiochemical parameters of the breeding habitats of the two significant black fly vector species, Simulium chumpornense Takaoka and Kuvangkadilok and S. nodosum Puri, from Laos. Genetic diversity of S. chumpornense in Laos was relatively high with maximum genetic divergence of 3.05% but no significant genetic differentiation between populations. Comparisons with conspecific populations from Thailand also found no genetic differentiation between the two countries. This possibly related to the recent history of this species, as a very recent (31,000 years ago) historical population expansion was detected. Physicochemical parameters of the breeding habitats suggest the ability to utilize diverse stream sizes from small flows (1 m wide) to huge rivers (290 m or more wide). Populations of S. nodosum from Laos had low genetic diversity with maximum genetic divergence of 2.56% and no genetic structuring among populations. Comparisons with those reported from other countries revealed five genetically divergent lineages (I–V) with minimum genetic divergence of 1.36%. The majority (42 of 52) of specimens from Laos belonged to lineage I and the remaining (10) comprised lineage II. Lineage I is the largest and representative of specimens from Thailand, Myanmar, Vietnam, Taiwan and Laos. Population history analysis revealed that lineage I had undergone recent demographic expansion dating back to 7000 years ago. This very recent population expansion resembles others reported from Thailand and possibly indicates a response to increasing human and domestic animals following the agricultural revolution. Breeding sites of S. nodosum are diverse in respect to elevation, velocity, water conductivity and streambed particle size. The ability to utilize a wide variety of breeding sites could promote the production of a large adult population, which can be a pest for humans and other animals.

Black flies (Diptera: Simuliidae) are significant pests and vectors transmitting pathogens to humans and other animals. However, knowledge of species diversity as well as their role as pests and vectors in Laos is limited, despite the country having abundant suitable lotic habitats, that is, running water. In this study, we collected wild adult black fly specimens from Laos. Both morphology and genetic data supported that they were Simulium khelangense Takaoka, Srisuka and Saeung, and therefore, a new distribution record for this species. Screening of the blood protozoa from 106 females detected Leucocytozoon (n = 7) and Trypanosoma (n = 9). Identifications of Leucocytozoon based on cytochrome b sequences in MalAvi database indicated that 5 specimens had identical sequences to those of 4 lineages (GALLUS17 [n = 2], GALLUS35 [n = 1], GALLUS37 [n = 1], and GALLUS41 [n = 1]) of unidentified species (i.e., Leucocytozoon sp.). The remaining 2 had no identical sequences but were very similar (99%) to GALLUS34 and GALLUS41 lineages. Identifications of Trypanosoma based on the small subunit rRNA indicated that all were T. avium. The results presented here further support the role of S. khelangense as a potential vector of Leucocytozoon and Trypanosoma as well as being a possible pest of domestic avian species.