Insects collected by light traps at Bloomington, Middleton, and Washington Field, near St. George, Utah, and at Beaver Dam Wash, Arizona, were pooled by species and assayed for arboviruses. Of 22,640 total insects, 61% were collected at Bloomington and Beaver Dam Wash and 11 of 13 virus isolations were from these 2 sites. There were 7 isolations of Western equine encephalitis virus, 1 from Culex tarsalis from Washington Field and 6 from Bloomington including 5 from Cx. tarsalis and 1 from a pool of rubbed Culex abdomens. One main drain virus was isolated from Culicoides variipennis from Middleton. Isolations from Beaver Dam Wash were a St. Louis encephalitis virus from Cx. tarsalis and a Jamestown Canyon virus from Culiseta inornata in 1973 and 1 Anopheles A group and 2 main viruses from Anopheles freeborni in 1974. Precipitin results on 83 blood-engorged insects indicated 34 cow-feedings, 15 at Washington Field and 12 at Bloomington; and 31 rabbit-feedings, 16 at Middleton, 9 at Bloomington, and 6 at Beaver Dam Wash.