Seasonal distribution and parity of host-seeking horse flies (Diptera: Tabanidae) from a pasture near Seven Sisters, Manitoba

Twenty species of Tabanidae in 3 genera (Hybomitra (15 spp.), Tabanus (4 spp.), Haematopota (1 sp.)) were caught in Manitoba horsefly traps from mid-May to mid-July in 1987, and from mid-May to mid-August in 1988. Hybomitra lurida and H. nitidifrons nuda peaked in abundance in late May to early June; H. illota and H. lasiophthalma in early June; H. affinis, H. arpadi and H. zonalis in mid-June; H. epistates and H. pechumani in late June to early July. Abundance of H. trepida peaked twice, in late June and early August. Tabanid density and diversity were greatest during June; few flies were present at the site after mid-July. For most species, at the beginning of the flight season, 80-100% of flies dissected were nulliparous. After approximately 1 month of flight activity, parity in all but 3 species reached levels approaching 100%, and remained high thereafter. H. lurida and H. nitidifrons nuda were 100% parous within 2 weeks of their first appearance in traps. Parity of H. trepida increased to 100% after 4 weeks, declined to 40% 2 weeks later, and returned to 100% after another 2 weeks.