Studies on the relative toxicity of different bio-rational insecticides against second instar larvae and adults of onion thrips, Thrips tabaci were carried out on Experimental Farm and in the laboratory, Faculty of Agriculture, University of Suez Canal. Eight insecticides Dipel 2x, BioFly, Agrin, BioGuard, Spinosad, Neemix, Mectin and Match were all evaluated for their relative toxicity towards T. tabaci with recommended dose, half of recommended dose and quarter of recommended dose in the laboratory and only recommended dose under field conditions. Spinosad was the most toxic among the tested insecticides followed by Mectin, Match and Agrin when used against thrips adults. The respective values of LC50 of those insecticides were 0.048 cm/l, 0.070 cm/l,0.079 cm/l and 0.137 g/l. Also, Spinosad was the most effective insecticide against second instar larvae followed descendingly by: Agrin, Match and Dipel 2x. Toxicity index values at LC50 level show such superior efficiency of Spinosad (100%) when applied against adults and second instar larvae of onion thrips under laboratory conditions. All insecticides under field conditions caused reduction of infestations of thrips. For the residual effect post application, all insecticides gave significant reductions in thrips numbers at the 21 day post treatment except for: Agrin and Match. Spinosad, Mectin, Neemix and BioFly gave the best control and continued to suppress thrips populations till 21 days after treatment. Spinosad was non harmful and Dipel 2x, Agrin were slightly harmful, BioGuard was significantly harmful whereas BioFly, Match and Mectin were very harmful to Orius albidipennis.
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