A study in east-central South Dakota during the summers of 1971 and 1972 evaluated insecticidal control of horn and face flies (Haematobia irritans(L.) andMusca autumnalisDe Geer, respectively) on cattle, as well as potential side effects to the insects of the bovine coprocoenosis. Three organophosphate compounds were aerially applied in ULV formulations: Ravap®, a 1:4 mixture of dichlorvos and Rabon® [2-chloro-1- (2,4,5-trichlorophenyl) vinyl dimethyl phosphate)], Rabon, and malathion. All 3 insecticides reduced the number of adult flies of both species for at least 1 day but for less than 1 wk. No residual control was noted. No significant effects to the dung biota could be attributed to Ravap or malathion. Rabon significantly (P=0.01) diminished only numbers ofPlatystethus americanusErichson,Falagria dissecta(Erichson),Aphodius fimetarius(L.), andCercyon pygmaeusIlliger, and, to a lesser degree (P=0.05), a miscellaneous group of unidentified dipterous larvae and larval hydrophilids. Most of the dung fauna, however, were unaffected by the insecticides.