A 75% reduction in horn fly populations lasted from two to four weeks following trial spray applications of insecticides in June, for two to six weeks following August treatments, and for the remainder of the fly season with most of the September grub control treatments. During the entire trial, most treatments kept horn fly populations below 100 flies per animal for five to six weeks after treatment. Grub control was excellent with all treatments, ranging from 96% to 99% control. Both common and northern grub infestations were effectively reduced. The split dose of Ruelene 8R provided excellent grub control as well as satisfactory horn fly control from August to the end of the fly season. There were no adverse effects observed on any animals treated during this Study.