Reduction in Emergence of Rhagoletis indifferens (Diptera: Tephritidae) from Sweet Cherries with Different Egg and Larval Distributions Using Newer Insecticides

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Western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), is the major insect pest of sweet cherry, Prunus avium (L.) L., in the Pacific Northwest of the U.S. To reduce fly populations in unharvested fruit following the completion of commercial harvest, it is important to control immature stages in cherry fruit. In this study, the goals were to (1) identify the susceptibility of the eggs and larvae to neonicotinoid and other insecticides and (2) determine the effects of these insecticides on larval emergence from sweet cherries with different egg and larval distributions (the relative percentages of different stages). Only 3.3% of eggs exposed for 15 sec to thiacloprid hatched, whereas 25.0 - 41.0% of eggs exposed to water only, spinosad, and imidacloprid hatched. Larval mortalities in cherries 48 - 52 h after being treated with imidacloprid, thiacloprid and acetamiprid were 50.0 - 66.7%, significantly higher than the 24.0% mortality in untreated cherries. Imidacloprid, thiamethoxam, thiacloprid, acetamiprid, and clothianidin were equally effective in reducing larval emergence when sprayed on cherries in which eggs were 94.2% of the immature stages, but imidacloprid and acetamiprid appeared to be the most effective when sprayed on cherries in which eggs were only 19.7% and 53.8% of the immature stages. Results indicate neonicotinoids are toxic to eggs and larvae of R. indifferens and that all are more effective in cherries against eggs than larvae. For fly control, the time interval between the last spray directed against adult flies and the first postharvest spray of neonicotinoids should be no more than 1 wk, to reduce chances eggs hatch and larvae develop.