The insecticides acephate, dichlorvos, and imidacloprid were assayed, using in vitro shoot cultures of apple (Malus×domestica Borkh.), to determine their phytotoxicity at several concentrations and their effectiveness for eradication of the Western Flower Thrip (Frankliniella occidentalis, Pergande) from infested apple shoot cultures. Commercial formulations of acephate (Orthene), dichlorvos (VaportapeII), and imidacloprid (Admire) and a technical grade of imidacloprid were used in the experiments. For acephate and imidacloprid, concentrations of 1 to 80 mg·L-1 a.i. in shoot culture medium were used, while for dichlorvos, a fumigant, particles of the formulated product containing concentrations of 0.7 to 6.4 mg a.i. were suspended in the head space of the 500-mL glass culture jar. Acephate, dichlorvos, and the technical grade of imidacloprid did not cause phytotoxicity and growth of shoot cultures was unaffected at all treatment concentrations tested after a 6-week treatment period. Imidacloprid (20 to 80 mg·L-1 of the commercial formulation) caused chlorosis at the end of the 6-week treatment period. None of the treatments tested resulted in the death of shoots. Thrips were eradicated by acephate or imidacloprid treatments of 5 mg·L-1 and by dichlorvos treatment of 0.7 mg per 500-mL culture jar. Shoot cultures grew normally after the treatment period. Chemical names used: O,S-dimethyl acetylphosphoramidothioate (acephate), 2,2- dichlorovinyl dimethyl phosphate(dichlorvos),1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine (imidacloprid).
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