Seasonal abundance, physiological age, and daily activity of host-seeking horse flies (Diptera: Tabanidae) at Seven Sisters, Manitoba, with an evaluation of permethrin spray treatments as a means of increasing the performance of growing beef heifers subject to horse fly attack
McElligott, Paul Edward Kaye
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Effects of biweekly permethrin treatments on the weight gain performance of growing beef heifers subject to attack by large numbers of blood-feeding tabanids was evaluated. In 1987 and 1988 respectively, groups of 55 and 72 heifers (of similar age and weight) were divided into two herds. Animals in one herd received biweekly whole-body sprays of permethrin (aqueous emulsion, 0.5% permethrin, applied at 1 L/animal), while the other herd was left untreated. Animals in both herds were weighed biweekly and those in one herd were treated concomitantly from early June through mid July. Permethrin spray treatments did not effectively reduce the impact of horse flies on the animals' weight gains. No consistent trend was apparent in differences between the average daily weight gains of animals in untreated and treated herds, and animals in both herds gained, on average, from 35.38 to 44.82 kg over the 6-week experimental period in both years. Tabanids were trapped from dawn until dusk using four Manitoba Horse Fly Traps (MHFT's) at Seven Sisters, from mid May until mid July in 1987, and from mid May until mid August in 1988, to determine the seasonal activity patterns of the various species present. Thirty one tabanid species in four genera (Hybomitra (15 spp.), Tabanus (4 spp.), Chrysops (11 spp.), Haematopota (1 sp.)), of which ten Hybomitra sp. were abundant, were present in MHFT catches. Hybomitra lurida (Fallen), and H. nitidifrons nuda (McDunnough) peaked in abundance in late May to early June; H. illota (Osten Sacken) and H. lasiophthalma (Macquart) in early June; H. affinis (Kirby), H. arpadi (Szilady), and H. zonalis (Kirby) in mid June; and H. epistates(O.S.) and H. pechumani Teskey & Thomas in late June to early August. Hybomitra trepid (McD.) peaked in abundance twice, in late June and early August. Tabanid density and diversity was greatest during June, and few flies were present at the site after mid July. Subsamples (10-30 flies) of daily trap catches were dissected to determine seasonal changes in the per cent parity of ten abundant Hybomitra species. At the beginning of the flight season, 80 to 100% of flies dissected were nulliparous. As the flight season progressed, however, an increasing proportion of flies captured were parous. After approximately one month of flight activity, parity in all but three species reached levels approaching 100%, and remained high thereafter. Hybomitra lurida and H. nitidifrons nuda were 100% parous within two weeks of their first appearance in trap catches, and parity of H. trepida increased to 100% after four weeks, declined to 40% two weeks later, and rose again to 100% after a further 2 weeks...