In the Amazon, the animals most used in animal husbandry are cattle (cattle and bubalines) and horses (equines), which are frequently attacked by hematophagous insects, especially the Tabanidae (horseflies), Culicidae (horseflies), Muscidae of the genus Stomoxys sp. (stable fly) and Hematobia irritans (horn fly), among others. Other insect groups deserve attention in these trophic relationships, especially muscid diptera that seek substances that leak from the bite lesions of hematophages. The objective of this study is to survey the hematophagous insects and other associated muscovid diptera that visit horses and cattle in search of blood and other substances that come from their bites, in the municipality of Belém and its surroundings. Observation and collection campaigns were carried out using a horse as bait. The data were processed by time of day (7 am - 6 pm) to define the fluctuation of the diurnal activity of the species. Measurements of climatic factors at the site were taken, also by hours, such as air temperature, relative humidity, brightness, and rainfall. The results of two full days of collecting in January, March, May, October, and December 2005 show that a total of 2,686 insect specimens were collected; the most abundant family was Tabanidae with a total of 1,360 specimens divided into 17 species. The most abundant Tabanidae species and their respective percentages of the total number of hematophages, collected attacking horses, were: Tabanus trivittatus (34.70%), T. occidentalis var. dorsovittatus (23.94%), Dichelacera bifacies (10.84 %). Stomoxys calcitrans, another important hematophagous species of the Muscidae family, was collected with 211 specimens attacking horse, corresponding to 15.44% of the total number of hematophages. Similar fluctuation was observed between the activity of hematophages and non-hematophages, by the hours of the day, and the activity peaks were related to the peak temperature of the day and the time of lower relative humidity. Another 1,142 specimens of two species of Chloropidae were collected from the horse, mainly associated with the bite lesions caused by the hematophages.
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