The toxicity and persistence in water of six organophosphate insecticide treatments used for control of Chironomus tepperi Skuse was evaluated. Each insecticide was applied to three rice bays (20 by 4 m) at the maximum recommended field rate. Fourth-instar C. tepperi were tested with water samples taken at various intervals after insecticide application. All treatments caused high (>97%) initial mortality of larvae with the exception of diazinon (0.13 ppm; average initial mortality, 47.3%). Temephos (0.06 ppm) showed the least residual activity, with no mortality occurring 5 d after application. Chlorfenvinphos (0.27 ppm) had the longest residual effect in water, resulting in 61.5% mortality 15 dafter application but only nominal activity at 20 d. The remaining treatments, diazinon, chlorpyrifos (0.08 ppm), trichlorfon (0.47 ppm), and malathion (0.32 ppm), provided <10% mortality after 7 d.
Document Type: Research Article
Publication date: June 1, 1991
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