Mortality of Rhagoletis pomonella (Diptera: Tephritidae) Exposed to Field-Aged Spinetoram, GF-120, and Azinphos-Methyl in Washington State

Wee L. Yee, Oriki Jack, Meralee J. Nash

Abstract


The effects of field-aged residues of the new semi-synthetic spinosyn insecticide spinetoram (Dow AgroSciences, Indianapolis, IN) and the spinosad bait GF-120 (Dow AgroSciences, Indianapolis, IN) on mortality of apple maggot fly, Rhagoletis pomonella (Walsh), were determined in Washington State. Mortality caused by spinetoram (100 g a.i./ha) sprayed on apples and aged 7 d was significantly lower than that caused by fresh spinetoram. Spinetoram (100 and 75 g a.i./ha) aged for 7 d caused less than or as much mortality as spinosad (100 g a.i./ha) aged for 7 d. Fresh spinetoram and azinphos-methyl aged 7 or 14 d caused similar mortality, but aged spinetoram and spinosad caused lower mortality than azinphos-methyl. Apples treated with spinetoram (75 g a.i./ha) and with spinosad aged 7 d and exposed to flies produced a few larvae. However, even though spinetoram (100 g a.i./ha) aged 14 d did not kill all female flies, no larvae emerged from apples sprayed with this treatment. In separate tests, 0-d, 3-d, and 7-d old GF-120 on apple leaves caused greater mortality than 14-d old GF-120. Results show that spinetoram and GF-120 when fresh are highly toxic to R. pomonella, but that both have relatively short residual activities under the hot, dry conditions typical of central Washington in summer. Ingredients that prolong their toxicities or make their toxins available to flies longer may be needed to optimize their performance. Also, results suggest that adult fly mortality caused by spinetoram is not an accurate predictor of larval emergence from apples, and that possible non-lethal effects caused by spinetoram need to be examined.

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