Spinosad Versus Spinetoram Effects on Kill and Oviposition of Rhagoletis indifferens (Diptera: Tephritidae) at Differing Fly Ages and Temperatures

Abstract

Western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), is a major quarantine pest of cherries ( Prunus spp.) in western North America that is often managed using the organic insecticide spinosad, but there is a question of whether its semisynthetic relative spinetoram is more toxic and better to use for controlling the fly. Here, spinosad and spinetoram effects on R. indifferens kill and oviposition were determined by exposing 3–4, 7–10, or 14–18 d old flies to dry spinosad and spinetoram (0.21 or 0.33 mg active ingredient [a.i.] per dish) and untreated cherries or to insecticide-treated cherries at 15.6, 22.5, and 29.4°C. Kill was not affected by fly age. Spinetoram killed more female flies by day 1 than spinosad at all temperatures. In both treatments, kill was lower at 15.6°C than 22.5 and 29.4°C, although a difference between 22.5 and 29.4°C was detected more often in spinosad treatments. Both insecticides killed 3–4 d old flies quickly enough to prevent oviposition, but neither prevented oviposition by 7–10 and 14–18 d old flies. Significantly, oviposition by flies exposed to spinosad and spinetoram did not differ at any temperature. Results indicate spinetoram is more toxic to R. indifferens than spinosad. However, this higher toxicity is not needed to prevent oviposition by younger flies. Furthermore, spinetoram residues are not sufficiently toxic to kill older flies quickly enough to reduce oviposition more than spinosad. Taken together, these conclusions imply that spinosad and spinetoram are equal for controlling R. indifferens infestations.