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Effects of the insect growth regulator diflubenzuron on insect emergence within littoral enclosures

Liber, K., Schmude, K.L., Corry, T.D.
Environmental entomology 1996 v.25 no.1 pp. 17-24
aquatic insects, Chironomidae, diflubenzuron, nontarget organisms, biological development, ponds, adverse effects, application rate, environmental exposure, Minnesota
Effects of the insect growth regulator diflubenzuron on insect emergence were investigated in littoral enclosures in a pond in northeastern Minnesota. Adult insects were captured with floating emergence traps before and after each of 2 applications with 4 different diflubenzuron rates. Emergence was reduced by up to 87, 96, and 99% relative to controls 4-8 d after the 1st application with 2.5, 7.0, and 30 micrograms/liter diflubenzuron, respectively. None of the affected populations returned completely to control levels by the time of the 2nd application. Reductions of less than or equal to 18% in insect emergence at the 0.7 micrograms/liter treatment were not statistically significant. Effects at the 2nd diflubenzuron application were similar to those of the 1st. Based on measured maximum exposure concentrations, the no observable and lowest observable effect concentrations for insect emergence were 1.0 and 1.9 micrograms/liter, respectively. Concentration-response analyses of the data indicated that the field EC50 for insect emergence inhibition ranged from 1.0 to 1.4 micrograms/liter, depending on the calculation method and on whether nominal or measured diflubenzuron concentrations were used. The estimated maximum acceptable toxicant concentration for Chironomidae was 0.7-0.8 micrograms/liter. Overall, significant adverse effects on insect emergence could be expected at diflubenzuron concentrations >1.0 micrograms/liter with the length and severity of effect being concentration dependent.