Control of Rhagoletis indifferens using thiamethoxam and spinosad baits under external fly pressure and its relation to rapidity of kill and residual bait activity

Control of western cherry fruit fly (Rhagoletis indifferens Curran) using thiamethoxam in sucrose bait (sucrose only) and spinosad bait (GF-120, spinosad in a mix of sugar, protein, ammonium acetate, and other ingredients) in cherry orchards with external fly pressure and the residual activity of these baits were studied in Washington state and Utah, U.S.A., in 2010 and 2011. Thiamethoxam baits applied weekly controlled larval infestations better than spinosad bait applied weekly in one of four trials and did not differ from spinosad bait applied weekly in the remaining trials. 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. Results suggest that when there is external fly pressure, the potentiality of thiamethoxam bait to kill mature R. indifferens more rapidly than spinosad bait may not always translate to better fly control. However, when sprays are applied every two weeks, the longer residual activity of thiamethoxam than spinosad bait does appear to translate to better fly control. This study presents thiamethoxam with sucrose as a new option for an effective bait spray against R. indifferens.

► Thiamethoxam baits controlled Rhagoletis indifferens infestations better than spinosad bait.
► Thiamethoxam baits killed flies quicker than spinosad bait.
► Thiamethoxam baits had longer residual activity than spinosad bait.
► The longer residual activity of thiamethoxam baits translates to better fly control.