Insecticide, sugar, and diet effects on feeding and mortality in Rhagoletis indifferens (Dipt., Tephritidae)

Western cherry fruit fly, Rhagoletis indifferens Curran (Dipt., Tephritidae), is the major quarantine insect pest of sweet cherry, Prunus avium (L.) L., in the Pacific North-west of the United States. Because of the zero tolerance for larvae in commercial cherries (State of Washington Department of Agriculture, Permanent Order No. 1099, effective 30 September 1968), cherry growers in this region continue to use insecticide products as their primary method for fly control, but effective organophosphate insecticides used in the past are no longer options (Food Quality Protection Act 1996; Reissig 2003). In recent years, spinosad bait (GF-120 Naturalyte Fruit Fly Bait, Dow AgroSciences, Indianapolis, IN), composed of 0.02% (w/v) spinosad, protein, sugar and other ingredients (Thomas and Mangan 2005), has gained popularity for use in control of R. indifferens (Warner 2008). The effectiveness of spinosad bait is dependent in part on fly feeding responses, which is related to hunger, as spinosad is more toxic to flies when ingested than when topically applied (Yee and Chapman 2005). Despite its effectiveness, spinosad bait does not always eliminate infestations of R. indifferens (Yee and Alston 2006; Yee 2007). Spinosad bait and spinosad (without bait) are two of six materials listed for use against R. indifferens