Controlling the impact of horse flies upon livestock.

Research was undertaken to determine how the treatment of cattle with a pyrethroid spray would affect the feeding and reproductive ability of Tabanidae in the Thistlethwaite Wildlife Management Area (WMA) in central Louisiana. Adult Holstein cows were placed daily in portable pens at 3 sites in each of 2 areas on the WMA. One group of 3 cows served as untreated controls, while the others were sprayed with ca. 1 gallon of 0.05% fenvalerate. The feeding time of different horsefly species (Tabanus fuscicostatus, T. lineola lineola and T. pallidescens) on both groups of cows was recorded. At each station, tabanids were also collected daily in traps, preserved and later dissected. Specimens were collected for 6 days before the cows were placed in the areas and for 8 days after the cows arrived. The feeding time of the 3 species of Tabanidae was significantly lower on treated cows (reduced by 26% for T. pallidescens, 33% for T. fuscicostatus and by 39% for T. l. lineola), and the amount of blood consumed by T. fuscicostatus was significantly reduced (by 29.3%). Changes in the parity rate in the 2 areas were significant between the pretreatment and treatment periods (the number of flies that had obtained a previous bloodmeal increased by 13.3% around untreated cows and decreased by 12.5% around treated cows). It is concluded that the incidence of tabanids on cattle can be reduced by the application of a pyrethroid spray, although further studies are necessary before the impact of this type of control on horsefly populations can be fully evaluated.