Anopheles quadrimaculatus and Psorophora columbiae adults were treated with a 1:1 and 1:5 mixture of technical permethrin and piperonyl butoxide. These mixtures (0.00075 lb AI/acre) at 100, 200, and 300 ft. downwind of application killed a similar (P < or = 0.05) percentage of Ps. columbiae ranging from 45.1 to 68.8% and 85.7 to 100.0% after 1 and 24 h posttreatment, respectively. Similar results were obtained at 1 and 24 h posttreatment against An. quadrimaculatus (0.00075 lb AI/acre) where percentage mortality ranged from 42 to 62% and 63 to 78% after 1 and 24 h posttreatment, respectively. At 24 h posttreatment, significantly more mortality (P < or = 0.05) occurred in An. quadrimaculatus than in Ps. columbiae for both the 1:1 and 1:5 formulations above, except at 100 ft. downwind. A higher dosage against An. quadrimaculatus (0.001 lb AI/acre) resulted in a higher mean mortality at 1 h posttreatment (45.1-79.1%) and 24 h posttreatment (59.2-86.0%) than at the lower dosage. A 25% increase in permethrin (0.001 lb AI/acre) vs. a 400% increase in piperonyl butoxide alone gave increases in mortality of 30.4% vs. 8.6%, respectively.