Technical Abstract: Control of western cherry fruit fly (Rhagoletis indifferens Curran) using thiamethoxam in sucrose bait and spinosad bait in cherry orchards under external fly pressure and its relation to rapidity of kill and residual bait activity were studied in Washington and Utah in 2010 and 2011. Thiamethoxam baits applied weekly controlled larval infestations as well as spinosad bait applied weekly in three of four trials and better than spinosad bait applied weekly in the remaining trial. Thiamethoxam baits applied every two weeks controlled larval infestations better than spinosad bait applied every two weeks in two of three trials, and did not differ statistically from spinosad bait applied weekly. Thiamethoxam bait that was aged on sweet cherry leaves in the field for 0, 7, 14, and 21 days killed flies more rapidly than spinosad bait that was aged for the same periods and reduced oviposition more than spinosad bait in the laboratory. Thiamethoxam bait retained activity up to 21 days of aging whereas spinosad bait lost activity after 14 or 21 days of aging. The ability of thiamethoxam bait to kill mature R. indifferens more rapidly than spinosad bait in the laboratory may not necessarily translate to better fly control when there is external fly pressure, but when sprays are applied every two weeks, the longer residual activity of thiamethoam than spinosad bait does appear to translate to better fly control.