20Horse flies (Diptera: Tabanidae) are hematophagous insects that cause direct and 21 indirect losses in livestock production and are important vectors of pathogens. The aim 22 the collected specimens. The environment was an important factor related to the 35 abundance of horse flies, as well as the mean temperature. The horse fly season in 36Tacuarembó started in September and ended in May, with three evident peaks, the most 37 important one during summer. No horse flies were caught during winter. Variations in 38 the prevalence of species in the different departments were observed, indicating the 39 need to carry out new sampling efforts in different areas. 40

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Horse flies (Diptera: Tabanidae) cause direct and indirect losses in livestock production and are important vectors of pathogens. The aim of this study was to determine the diversity and seasonality of horse fly species at an experimental farm in Tacuarembó and the diversity of species in different departments of Uruguay. For 20 months, systematic collections were performed in two different environments at the experimental farm using Nzi and Malaise traps. In addition, nonsystematic collections were performed at farms located in the departments of Paysandú, Tacuarembó and Colonia. A total of 3,666 horse flies were collected, and 16 species were identified. These species included three species that had not been previously recorded in Uruguay, namely, Dasybasis ornatissima (Brèthes), Dasybasis missionum (Macquart), and Tabanus aff. platensis Brèthes, and a species that had not been previously taxonomically described (Tabanus sp.1). Among the systematically captured samples, the most abundant species were Tabanus campestris Brèthes, T. aff. platensis and D. missionum, representing 77.6% of the collected specimens. The horse fly season in Tacuarembó started in September and ended in May. No horse flies were caught during winter. Variations in the prevalences of species in the different departments were observed, which indicates the need for new sampling efforts. Horse flies (Tabanidae) are hematophagous dipterans that cause direct losses to livestock production due to irritation, stress, and blood loss in animals, particularly cattle and horses 1. In fact, horse flies have directly resulted in decreases in the weight gain of cattle of 0.1 to 1 kg per day 1,2. Economic losses are directly related to the number of horse flies present in the environment 3. In addition to the losses caused by the direct effects of horse flies, these pests cause indirect losses due to their role as a mechanical vector of numerous pathogens, including those causing bovine leukosis, vesicular stomatitis, equine infectious anemia, swine fever, anthrax, and tularemia, as well as various species of trypanosomes and Anaplasma marginale 4,5. These indirect losses might be even more important than the direct losses. Not all members of the Tabanidae family have the same potential for transmitting disease agents because they exhibit various hematophagous behaviors and present different anatomical characteristics, which determine the amount of blood that they can transport 5-7. According to the Köppen classification, Uruguay has a subtropical climate with four marked seasons, a mean annual temperature of 17.29 °C and a mean humidity of 76.03% 8. Uruguay, along with the state of Rio Grande do Sul (Brazil) and the province of Buenos Aires (Argentina), comprise the Pampa biome. The emergence of the first generation of horse flies depends on the latitude and the season 9,10. Horse flies are active mostly in warm seasons when both the relative humidity and temperature are high. Only females are hematophagous, and the adult longevity varies from two to th...