BIONOMICS OF THE HORN FLY (HAEMATOBIA IRRITANS) IN WESTERN NEBRASKA

Field investigations were undertaken to determine the economic injury level of horn flies on cow-calf groups in western Nebraska. The groups utilized contained one group with cows having one fenvalerate eartag, another group with the cows having one fenvalerate eartag and the calves wormed, and the last herd had no treatment at all. Over the three year study eartags were effective in controlling horn flies (the average for the treated groups was less than 2 flies/cow); the untreated group averated 197 flies/cow. No differences in weight gains were noted between cow herds treated for fly control and untreated cow herds. Field investigations were undertaken to determine if fly control utilizing fenvalerate-impregnated eartags affected the dung insect macro fauna. Despite the reduction in horn fly larval numbers in dung pats of eartagged cattle, no difference in other dung faunal species was apparent when compared with dung pats from untreated cattle. A two year study on parasites of horn fly pupae in the Sandhills of Nebraska revealed a new host record for the figitid Trischiza atricornis (Ashmead). Trischiza atricornis accounted for 75.2% of the observed parasitism, and parasitized 17% of 557 pupae. The effect of horn flies on cattle bunching behavior, conducted in the Sandhills of Nebraska, revealed no significant differences between eartagged and untreated cattle groups. The average observed infestation levels over the three years for the treated and untreated groups was less than 2 flies/cow and 197 flies/cow, respectively. Studies on the distribution and abundance of horn flies on cattle revealed that horn flies "preferred" black over red hide colored cattle in western Nebraska. Furthermore, a diurnal movement of flies on cattle was observed. Flies, in the morning hours, were primarily on the back, and then as the temperature increased to midday the flies moved to the sides and belly midline. Then as temperatures receded in the late afternoon, the flies returned to the backs of the cattle.