Tabanids were collected during 2 consecutive summers from 3 counties in New York using a canopy trap and insect net. Twenty-seven per cent of all fly specimens (N equals 641) representing 69% of the species collected (N equals 36) were infected with flagellates. Tabanid intestines harbored amastigote, choanomastigote, and epimastigote forms. Epimastigotes were frequently found, and trypomastigotes and choanomastigotes rarely found in cultures of tabanid intestinal flagellates. Epimastigote and trypomastigote forms closely resembled Trypanosoma theileri-like trypanosomes reported from ruminants.
The tabanids, or horse flies and deer flies, are well known to dairy farmers and livestock producers as well as to campers, fishermen, and outdoor enthusiasts as annoying and pain-inflicting inhabitants of most wooded areas of Illinois. These large and persistent flies impart a painful bite and can occur in large enough numbers to make canoeing and hiking virtually impossible. The tabanid fauna of Illinois has never been studied, although several of the surrounding states have published various reports: Indiana (Burton 1975; Meyer & Sanders 1975), Wisconsin (Roberts & Dicke 1958), Iowa (Richards &: Knight 1967), Missouri (Andrews & Wingo 1975), Tennessee (Goodwin 1966), Michigan (Hays 1956), Ohio (Hine 1903), Minnesota (Philip 1931), and Arkansas (Schwardt 1936; Schwardt & Hall 1930). This study is intended to make available in brief form our present knowledge of the tabanids in the central United States, with keys for their determination, and the distribution of those species occurring in Illinois. No attempt is made to give detailed taxonomic descriptions of species. If needed, these can be found for most species in the papers of Brennan (1935) and Stone (1938). Philip (1954, 1955) has keys to all the North American Pangoniinae and Chrysopsinae known at that time. The most recent list of the North American species of Tabanidae is given by Philip (1965).
Female. Length. 9.6 mm.Head. Frontoclypeus and cheeks grayish white pollinose with rather long white hairs which are quite dense below; a small area in center of frontoclypeus denuded; also two very small denuded areas on the lower portion of each cheek; front above antennae grayish white pollinose shading to yellowish brown toward the vertex; front and vertex with many long black hairs. Frontal callosity brownish black and somewhat shining; about one half width of front.
Casual examination of a series of three Silvius would indicate they are distinct from any described species. Examination in detail, however, shows a close relationship to S. pollinosus Williston. Since the material on hand is limited, it is probably better to regard them as representing a subspecies of pollinosus than to give this new form full specific rank.
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