COLLEGE STATION—High populations of horse flies, a stubborn and difficult biting fly to control, have caused problems for Texas livestock producers this year, according to Dr. Sonja Swiger, AgriLife Extension entomologist, of Stephenville. Dr. Swiger said reports of horse-fly infestations are higher than she’s ever experienced during her 11-year career. “It’s the worst year I’ve seen,” she said…