Diversity, Distribution and Host Blood Meal Analysis of Adult Black Flies (Diptera: Simuliidae) from Thailand

Simple Summary Black flies are small-sized (<6 mm) blood-sucking insects belonging to the family Simuliidae of the order Diptera. More than 2400 species have been recorded globally, and approximately 6% (145 species) are found in Thailand. Many black fly species are pests to humans and other animals. They also transmit pathogens such as viruses, protozoa and filarial nematodes to humans and other animals, including economically significant livestock. Therefore, knowledge of species the diversity and distribution of wild adults, as well as host blood sources, provides important information required to prevent problems related to black fly biting. In this study, we collected 7706 wild adult black flies over a seven-year period (2017–2023) from diverse natural habitats in Thailand. In total, 16 black fly taxa were recorded; one of them, Simulium yvonneae Takaoka and Low, is a new record for the country. The majority of the specimens were Simulium asakoae Takaoka and Davies complex, contributing 74% of the total number of specimens collected. This species predominantly occurs in forest and urban habitats. The second most abundant species, S. chumpornense Takaoka and Kuvangkadilok (16% of the total specimens collected) was predominant in domestic animal shelters. Host blood meal identification using molecular approaches revealed four vertebrate host species: humans, chickens, turkeys and water buffalo. Abstract 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 (<800 m)-elevation areas. Simulium furvum Takaoka and Srisuka; S. phurueaense Tangkawanit, Wongpakam and Pramual; and S. nr. phurueaense were only found in high (>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.